Found 53 papers in cond-mat
Date of feed: Tue, 23 May 2023 00:30:00 GMT

Search terms: (topolog[a-z]+)|(graphit[a-z]+)|(rhombohedr[a-z]+)|(graphe[a-z]+)|(chalcog[a-z]+)|(landau)|(weyl)|(dirac)|(STM)|(scan[a-z]+ tunne[a-z]+ micr[a-z]+)|(scan[a-z]+ tunne[a-z]+ spectr[a-z]+)|(scan[a-z]+ prob[a-z]+ micr[a-z]+)|(MoS.+\d+|MoS\d+)|(MoSe.+\d+|MoSe\d+)|(MoTe.+\d+|MoTe\d+)|(WS.+\d+|WS\d+)|(WSe.+\d+|WSe\d+)|(WTe.+\d+|WTe\d+)|(Bi\d+Rh\d+I\d+|Bi.+\d+.+Rh.+\d+.+I.+\d+.+)|(BiTeI)|(BiTeBr)|(BiTeCl)|(ZrTe5|ZrTe.+5)|(Pt2HgSe3|Pt.+2HgSe.+3)|(jacuting[a-z]+)

Foldy-Wouthuysen transformation and multiwave states of a graphene electron in external fields and free (2+1)-space. (arXiv:2305.11879v1 [cond-mat.mes-hall])
Alexander J. Silenko

The relativistic Foldy-Wouthuysen transformation is used for an advanced description of planar graphene electrons in external fields and free (2+1)-space. It is shown that the initial Dirac equation should contain usual Dirac matrices but not the Pauli ones. The spin of graphene electrons is not the isotopic spin and takes the values $\pm1/2$. The exact Foldy-Wouthuysen Hamiltonian of a graphene electron in uniform and nonuniform magnetic fields is derived. The exact energy spectrum agreeing with experimental data and exact Foldy-Wouthuysen wave eigenfunctions are obtained. These eigenfunctions describe multiwave (structured) states in (2+1)-space. It is proven that the Hermite-Gauss beams exist even in the free space. In the multiwave Hermite-Gauss states, graphene electrons acquire nonzero effective masses dependent on a quantum number and move with group velocities which are less than the Fermi velocity. Graphene electrons in a static electric field also can exist in the multiwave Hermite-Gauss states defining non-spreading coherent beams. These beams can be accelerated and decelerated.

Mechanical, Optical and Thermoelectric Properties of Janus BiTeCl Monolayer. (arXiv:2305.11922v1 [cond-mat.mtrl-sci])
Poonam Chauhan, Jaspreet Singh, Ashok Kumar

We report mechanical, optical and thermoelectric properties of recently fabricated Janus BiTeCl monolayer using density functional and semi-classical Boltzmann transport theory. Janus BiTeCl monolayer exhibits a direct bandgap, high carrier mobility (~10$^3$ cm$^2$V$^{-1}$s$^{-1}$) and high optical absorption in the UV-visible region. The mechanical behavior of the Janus BiTeCl monolayer is nearly isotropic having an ideal tensile strength ~ 15 GPa. The higher value of the Gruneisen parameter ($\gamma$), a low value of phonon group velocity (vg), and very little phonon scattering time ($\tau_p$) lead to low lattice thermal conductivity (1.46 W/mK) of Janus BiTeCl monolayer. The combined effect of thermal conductivity and electronic transport coefficients of Janus BiTeCl monolayer results in the figure of merit (ZT) in the range of 0.43-0.75 at 300-500 K. Our results suggest Janus BiTeCl monolayer be a potential candidate for optoelectronic and moderate temperature thermoelectric applications.

Two-Dimensional $\beta$-PdX$_2$ (X = S, Te) Monolayers for Efficient Solar Energy Conversion Applications. (arXiv:2305.11924v1 [cond-mat.mtrl-sci])
Mukesh Jakhar, Ashok Kumar

The search for highly effective and environmentally safe photocatalysts for water splitting and photovoltaic solar cells is essential for renewable solar energy conversion and storage. Based on first principles calculations, we show that novel 2D $\beta$-PdX$_2$ (X = S, Te) monolayer possesses excellent stabilities and great potentials in solar energy conversion applications. Comprehensive studies show that the $\beta$-PdX$_2$ monolayer exhibits semiconductor characteristics with an indirect gap, suitable band alignment, efficient carrier separation, and high solar to hydrogen (STH) efficiencies, supporting its good photoelectronic performance. The surface catalytic and adsorption/intercalation energies calculation reveals that the photogenerated holes have adequate driving forces to render hydrogen reduction half-reactions to proceed spontaneously and the ability to cover and incorporate water molecules on $\beta$-PdX$_2$ monolayer. Besides, the $\beta$-PdX$_2$ monolayer is promising donor material for excitonic solar cells with high photovoltaic performance. More importantly, due to suitable donor band gap and small conduction band offset in the proposed type-II heterostructure, the calculated power conversion efficiencies (PCE) is calculated up to ~23% ($\beta$-PdX$_2$/WTe$_2$), ~21% ($\beta$-PdX$_2$/ MoTe$_2$) and ~18% ($\beta$-PdTe2/$\beta$-PdX$_2$), making it a promising candidate for solar energy conversion applications.

Fate of multipolar physics in $5d^2$ double perovskites. (arXiv:2305.11939v1 [cond-mat.str-el])
Ahmed Rayyan, Xiaoyu Liu, Hae-Young Kee

In a cubic environment, the ground state of spin-orbit coupled $5d^2$ ions is a non-Kramers $E_g$ doublet, which hosts quadrupole and octupole moments. A series of $5d^2$ osmium double perovskites Ba$_2M$OsO$_6$ (M = Mg, Ca, Zn, Cd) have recently been proposed to exhibit multipolar orders. We investigate the structural properties of these materials using $\textit{ab}$-$\textit{initio}$ calculations and find that the cubic structure is unstable for the Cd compound while the Mg, Ca, and Zn materials retain $Fm\bar{3}m$ symmetry. We show that Ba$_2$CdOsO$_6$ favours a rhombohedral $R\bar{3}$ structure characterized by $a^-a^-a^-$ octahedral tiltings as indicated by unstable $\mathcal{T}_{1g}$ phonon modes. Trigonal distortions split the excited $T_{2g}$ triplet into an $E'_g$ doublet and an $A_g$ singlet, which may cross energy levels with the $E_g$ doublet and suppress the multipolar physics. We find a window where $E_g$ remains the lowest energy state under trigonal distortion, enabling the emergence of multipole phases in non-cubic crystal environments.

The 4D Camera: an 87 kHz direct electron detector for scanning/transmission electron microscopy. (arXiv:2305.11961v1 [physics.ins-det])
Peter Ercius, Ian J. Johnson, Philipp Pelz, Benjamin H. Savitzky, Lauren Hughes, Hamish G. Brown, Steven E. Zeltmann, Shang-Lin Hsu, Cassio C.S. Pedroso, Bruce E. Cohen, Ramamoorthy Ramesh, David Paul, John M. Joseph, Thorsten Stezelberger, Cory Czarnik, Matthew Lent, Erin Fong, Jim Ciston, Mary C. Scott, Colin Ophus, Andrew M. Minor, and Peter Denes

We describe the development, operation, and application of the 4D Camera -- a 576 by 576 pixel active pixel sensor for scanning/transmission electron microscopy which operates at 87,000 Hz. The detector generates data at approximately 480 Gbit/s which is captured by dedicated receiver computers with a parallelized software infrastructure that has been implemented to process the resulting 10 - 700 Gigabyte-sized raw datasets. The back illuminated detector provides the ability to detect single electron events at accelerating voltages from 30 - 300 keV. Through electron counting, the resulting sparse data sets are reduced in size by 10 - 300x compared to the raw data, and open-source sparsity-based processing algorithms offer rapid data analysis. The high frame rate allows for large and complex 4D-STEM experiments to be accomplished with typical STEM scanning parameters.

Floquet-Driven Indirect Exchange Interaction Mediated by Topological Insulator Surface States. (arXiv:2305.11963v1 [cond-mat.mes-hall])
Modi Ke, Mahmoud M. Asmar, Wang-Kong Tse

Light drives offer a potential tool for the dynamical control of magnetic interactions in matter. We theoretically investigate the indirect exchange coupling between two parallel chains of magnetic impurities on the surface of a topological insulator, driven by a time-periodic circularly polarized light field in the high-frequency, off-resonant, regime. We derive a closed-form analytic expression for the spin susceptibility of the photon-dressed topological insulator surface states and obtain the irradiation dependence of the Ising, Heisenberg, and Dzyaloshinsky-Moriya exchange couplings between the impurity chains. Our results show a two-pronged modification of these exchange couplings by periodic drives. First, the RKKY oscillation period of the exchange couplings can be extended by enhancing the driving strength. Secondly, increasing driving strength enhances the envelope of RKKY oscillations of the Heisenberg-type while suppressing those of the Ising-type and Dzyaloshinsky-Moriya-type. Our work provides useful insights for realizing Floquet engineering of collinear and non-collinear indirect exchange interactions in topological insulating systems.

Nanopore creation in graphene at the nanoscale for water desalination. (arXiv:2305.11970v1 [cond-mat.mes-hall])
Sidi Abdelmajid Ait Abdelkader, Ismail Benabdallah, Mohammed Amlieh, Abdelouahad El Fatimy

Creating nanopores in graphene is a powerful tool for engineering its properties. Nanopores in graphene tune their electrical, optical, magnetic, and mechanical properties. However, controlling nanopores formation at the nanoscale level remains a significant challenge. We report an easy method to control nanopore sizes using argon-plasma magnetron sputtering. By calculating and measuring Raman spectra, we show that the nano-pores in graphene are controllable and size-tunable. Furthermore, we report that the graphene Raman mode around 1450 cm-1, which was attributed to the substrate effect, is due to nanopores.

We also propose here a novel graphene device-based water filtration. Our proposed concept of two graphene electrodes with nanopores on the substrate (SiC and SiO2) makes it possible to have the highest permeability value, keeping almost 100 % salt rejection and improving its mechanical properties. These reported results are essential for developing water desalination membranes based on graphene devices.

Topological Kinetic Crossover in a Nanomagnet Array. (arXiv:2305.11973v1 [cond-mat.mes-hall])
Xiaoyu Zhang, Grant Fitez, Shayaan Subzwari, Nicholas S. Bingham, Ioan-Augustin Chioar, Hilal Saglam, Justin Ramberger, Chris Leighton, Cristiano Nisoli, Peter Schiffer

Ergodic kinetics, which are critical to equilibrium thermodynamics, can be constrained by a system's topology. We study a model nanomagnetic array in which such constraints visibly affect the behavior. In this system, magnetic excitations connect into thermally active one-dimensional strings whose motion can be imaged in real time. At high temperatures, we observe the merging, breaking, and reconnecting of strings, resulting in the system transitioning between topologically distinct configurations. Below a crossover temperature, the string motion is dominated by simple changes in length and shape. In this low temperature regime, the system is energetically stable because of its inability to explore all possible topological configurations. This kinetic crossover suggests a generalizable conception of topologically broken ergodicity and limited equilibration.

Cooperative rheological state-switching of enzymatically-driven composites of circular DNA and dextran. (arXiv:2305.11987v1 [cond-mat.soft])
Juexin Marfai, Ryan J. McGorty, Rae M. Robertson-Anderson

Polymer topology, which plays a principal role in the rheology of polymeric fluids, and non-equilibrium materials, which exhibit time-varying rheological properties, are topics of intense investigation. Here, we push composites of circular DNA and dextran out-of-equilibrium via enzymatic digestion of DNA rings to linear fragments. Our time-resolved rheology measurements reveal discrete state-switching, with composites undergoing abrupt transitions between dissipative and elastic-like states. The gating time and lifetime of the elastic-like states, and the magnitude and sharpness of the transitions, are surprisingly decorrelated from digestion rates and non-monotonically depend on the DNA fraction. We model our results using sigmoidal two-state functions to show that bulk state-switching can arise from continuous molecular-level activity due to the necessity for cooperative percolation of entanglements to support macroscopic stresses. Our platform, coupling the tunability of topological composites with the power of enzymatic reactions, may be leveraged for diverse material applications from wound-healing to self-repairing infrastructure.

Even spheres as joint spectra of matrix models. (arXiv:2305.12026v1 [math.OA])
Alexander Cerjan, Terry A. Loring

The Clifford spectrum is a form of joint spectrum for noncommuting matrices. This theory has has been applied in photonics, condensed matter and string theory. In applications, the Clifford spectrum can be efficiently approximated using numerical methods. Here we examine the higher-dimensional spheres that can arise from theoretical examples. We also look at how to generate five real symmetric almost commuting matrices that have a $K$-theoretical obstruction to being close to commuting matrices. For this, we look to matrix models of topological electric circuits.

Determining the upper critical magnetic field for N-doped lutetium hydride directly from the source data files in Dasenbrock-Gammon et al., Nature $\underline{615}$, 244 (2023). (arXiv:2305.12065v1 [cond-mat.supr-con])
Dale R. Harshman, Anthony T. Fiory

The Ginzburg-Landau-based upper critical magnetic field $H_{\textrm{C2}}$ (0) $\approx$ 88 T for N-doped lutetium hydride, reported in Dasenbrock-Gammon et al., Nature $\textbf{615}$, 244 (2023), is obtained therein by modeling resistance behavior, defining transitions widths, and applying magnetic fields $H$ = 1 T and 3 T. A method is presented herein for determining the critical temperature $T_{\textrm{C}}$ ($H$) directly from the resistance drops in the source data, implying a temperature slope -d$H_{\textrm{C2}}$ /d$T$ of 0.46(6) ${-}$ 0.51(5) T/K and, by applying pure BCS theory, an $H_{\textrm{C2}}$ (0) of 71(10) ${-}$ 79(8) T.

Probing the Magnetic State of a Kitaev Material with Graphene. (arXiv:2305.12116v1 [cond-mat.str-el])
Jingtian Shi, A.H. MacDonald

Single layer $\alpha$-ruthenium trichloride ($\rm\alpha-RuCl_3$) has been proposed as a potential quantum spin liquid. Graphene/$\rm RuCl_3$ heterobilayers have been extensively studied with a focus on their large interlayer electron transfer driven by a chemical potential difference, which dopes both materials. Here we examine the possibility of probing the magnetic state of the \ce{RuCl_3} layer by measuring transport in an adjacent graphene layer. We perform self-consistent Hartree-Fock calculations on a Hubbard-Kanamori model of the $4d^5$ $t_{2g}$ electrons of $\rm \alpha-RuCl_3$ and confirm that out-of-plane ferromagnetic and zigzag antiferromagnetic states are energetically competitive. We show that the influence of hybridization between graphene and $\rm RuCl_3$ bands is strongly sensitive to the magnetic configuration of $\rm RuCl_3$ and the relative orientations of the two layers, and argue that it can alter the conductivity of the graphene layer. Our analysis can be applied to any van der Waals heterobilayer system with weak interlayer hybridization and allows for arbitrary lattice constant mismatch and relative orientation.

Non-Abelian physics in light and sound. (arXiv:2305.12206v1 [physics.optics])
Yi Yang, Biao Yang, Guancong Ma, Jensen Li, Shuang Zhang, C. T. Chan

There has been a recent surge of interest in using light and sound as platforms for studying non-Abelian physics. Through a kaleidoscope of physical effects, light and sound provide diverse ways to manipulate their degrees of freedom to constitute the Hilbert space for demonstrating non-Abelian phenomena. The review aims to provide a timely and comprehensive account of this emerging topic. Starting from the foundation of matrix-valued geometric phases, we cover non-Abelian topological charges, non-Abelian gauge fields, non-Abelian braiding, non-Hermitian non-Abelian phenomena, and their realizations with photonics and acoustics. This topic is fast evolving at the intersection of atomic, molecular, optical physics, condensed matter physics, and mathematical physics, with fascinating prospects ahead.

Ba9RE2(SiO4)6 (RE=Ho-Yb): A New Family of Rare-earth based Honeycomb Lattice Magnets. (arXiv:2305.12214v1 [cond-mat.str-el])
Andi Liu, Fangyuan Song, Zhaohu Li, Malik Ashtar, Yuqi Qin, Dingjun Liu, Zhengcai Xia, Jingxin Li, Zhitao Zhang, Wei Tong, Hanjie Guo, Zhaoming Tian

Rare-earth (RE) based honeycomb-lattice materials with strong spin-orbit coupled Jeff=1/2 moments have attracted great interest as a platform to realize Kitaev quantum spin liquid (QSL) state. Herein, we report the discovery of a new family of RE based honeycomb-lattice magnets Ba9RE2(SiO4)6(RE=Ho-Yb), which crystallize into the rhombohedral structure with space group R-3. In these serial compounds, magnetic RE3+ ions are arranged on a perfect honeycomb lattice within the ab-plane and stacked in the ABCABC-type fashion along the c-axis. All Ba9RE2(SiO4)6(RE=Ho-Yb) polycrystals exhibit the dominant antiferromagnetic interactions and absence of magnetic order down to 2 K. In combination with the magnetization and electron spin resonance (ESR) results, distinct anisotropic magnetic behaviors are proposed for compounds with different RE ions. Moreover, the synthesized Ba9Yb2Si6O24 single crystals show large magnetic frustration and no long-range magnetic ordering down to 0.15 K, being a possible QSL candidate state. These serial compounds are attractive for exploring the exotic magnetic phases of Kitaev materials with 4f electrons.

Magnetostriction-driven muon localisation in an antiferromagnetic oxide. (arXiv:2305.12237v1 [cond-mat.str-el])
Pietro Bonfà, Ifeanyi John Onuorah, Franz Lang, Iurii Timrov, Lorenzo Monacelli, Chennan Wang, Xiao Sun, Oleg Petracic, Giovanni Pizzi, Nicola Marzari, Stephen J. Blundell, Roberto De Renzi

Magnetostriction drives a rhombohedral distortion in the cubic rock salt antiferromagnet MnO at the N\'eel temperature $T_{N}=118$ K. As an unexpected consequence we show that this distortion acts to localize the site of an implanted muon due to the accompanying redistribution of electron density. This lifts the degeneracy between equivalent sites, resulting in a single observed muon precession frequency. Above $T_{N}$, the muon instead becomes delocalized around a network of equivalent sites. Our first-principles simulations based on Hubbard-corrected density-functional theory and molecular dynamics are consistent with our experimental data and help to resolve a long-standing puzzle regarding muon data on MnO, as well as having wider applicability to other magnetic oxides.

Exsolution of oxygen impurity from diamond lattice and formation of pressurized CO2-I precipitates. (arXiv:2305.12243v1 [cond-mat.mtrl-sci])
Andrei A. Shiryaev, Yurii Chesnokov, Alexander L. Vasiliev, Thomas Hainschwang

Diamond single crystals showing Infra-red features of pressurized CO2-I phase were studied using Transmission Electron Microscopy (TEM) and tomography. Numerous O-containing precipitates with sizes up to 45 nm are observed. The absolute majority of these precipitates decorate dislocation loops or are located inside them; individual scattered precipitates are also present. Morphology of the precipitates varies from quasi-isometric octahedra to highly flattened elongated ones. Close association of the precipitates with the dislocation loops implies their formation by exsolution of oxygen impurity from diamond lattice; the size distribution of the precipitates suggests that the equilibrium state is not yet reached. Presumably, the morphology and precise chemical composition depend on P-T-t evolution of the diamond crystal and corresponding changes in oxygen supersaturation in the lattice. The CO2-containing diamonds often contain micron-sized hexagonal lamellar inclusions. TEM investigation of a lamellae reveals that it consists of high quality graphite showing partial epitaxial relation with comprising diamond. The gap between the graphite and diamond may be enriched with oxygen impurity.

Healing of a Topological Scar: Coordination Defects in a Honeycomb Lattice. (arXiv:2305.12246v1 [cond-mat.mtrl-sci])
Benjamin Katz, Vincent Crespi

A crystal structure with a point defect typically returns to its ideal local structure upon moving a few bond lengths away from the defect; topological defects such as dislocations or disclinations also heal rapidly in this regard. Here we describe a simple point defect -- a two-fold atom incorporated at the growth edge of a 2D hexagonal honeycomb material -- whose healing may require a defect complex with 50 or more atoms. $\textit{Topologically}$ the two-fold atom disappears into a single 'long bond' between its neighbors, thereby inducing a pentagonal disclination. However, $\textit{chemically}$ this disclination occupies as much physical space as a six-fold ring. This incompatibility of chemistry and topology can cause a ''ringing'' of the Gaussian curvature that creates an expansive healing region and may even spawn a semi-infinite grain boundary propagating outwards from the topological scar.

Candidate local parent Hamiltonian for 3/7 fractional quantum Hall effect. (arXiv:2305.12400v1 [cond-mat.str-el])
Koji Kudo, A. Sharma, G. J. Sreejith, J. K. Jain

While a parent Hamiltonian for Laughlin $1/3$ wave function has been long known in terms of the Haldane pseudopotentials, no parent Hamiltonians are known for the lowest-Landau-level projected wave functions of the composite fermion theory at $n/(2n+1)$ with $n\geq2$. If one takes the two lowest Landau levels to be degenerate, the Trugman-Kivelson interaction produces the unprojected 2/5 wave function as the unique zero energy solution. If the lowest three Landau levels are assumed to be degenerate, the Trugman-Kivelson interaction produces a large number of zero energy states at $\nu=3/7$. We propose that adding an appropriately constructed three-body interaction yields the unprojected $3/7$ wave function as the unique zero energy solution, and report extensive exact diagonalization studies that provide strong support to this proposal.

Collective excitations in chiral Stoner magnets. (arXiv:2305.12508v1 [cond-mat.mes-hall])
Zhiyu Dong, Olumakinde Ogunnaike, Leonid Levitov

We argue that spin and valley-polarized metallic phases recently observed in graphene bilayers and trilayers support chiral edge modes that allow spin waves to propagate ballistically along system boundaries without backscattering. The chiral edge behavior originates from the interplay between the momentum-space Berry curvature in Dirac bands and the geometric phase of a spin texture in position space. The edge modes are weakly confined to the edge, featuring dispersion which is robust and insensitive to the detailed profile of magnetization at the edge. This unique character of edge modes reduces their overlap with edge disorder and enhances the mode lifetime. The mode propagation direction reverses upon reversing valley polarization, an effect that provides a clear testable signature of geometric interactions in isospin-polarized Dirac bands.

Active dislocations and topological traps govern dynamics of spiraling filamentous cyanobacteria. (arXiv:2305.12572v1 [cond-mat.soft])
Xingting Gong, Manu Prakash

Activity can organize matter in unique configurations inaccessible to equilibrium systems, including a sundry of spiraling shapes seen in nature that range from galaxies to living tissues to fossilized stromatolites. How these dynamic yet stable patterns form in motile active systems that span a range of length and time scales remains an open question. Here we study the collective gliding dynamics of ultra-long filamentous cyanobacteria confined in two dimensions and present the discovery of an emergent pattern we call ``active spirals". Individual filaments in the spiral bulk remain confluent due to adhesion forces and exhibit reversible gliding motility. Thus individual filaments undergo bidirectional movement and the spiral object as a whole has no fixed vorticity. Using single filament tracking, we discover that spirals permit the radial flux of material as filaments shear past one another. We demonstrate that these rearrangements can be entirely described by topological rules of interaction between filaments tips. We thus reduce the dynamics of a spiral to a set of active dislocations (corresponding to the filament tips) on a polar coordinate lattice and show that we can reproduce and predict the material flux in the system. Finally, we present a discovery of a novel topological trap present in these spirals, and is induced purely by the geometric chirality of long winding filaments with winding number greater than zero. A topological trap creates boundaries in the spiral across which material cannot flow, leading to persistent structures that are topologically locked for the lifetime of the system. The emergent mechanics of active spirals presented here sheds light on the critical role of adhesion forces, activity and geometry in the formation of long-term, stable, yet dynamic active patterns.

Helical boundary modes from synthetic spin in a plasmonic lattice. (arXiv:2305.12609v1 [cond-mat.mes-hall])
Sang Hyun Park, Michael Sammon, Eugene Mele, Tony Low

Artificial lattices have been used as a platform to extend the application of topological physics beyond electronic systems. Here, using the two-dimensional Lieb lattice as a prototypical example, we show that an array of disks which each support localized plasmon modes give rise to an analog of the quantum spin Hall state enforced by a synthetic time reversal symmetry. We find that an effective next-nearest-neighbor coupling mechanism intrinsic to the plasmonic disk array introduces a nontrivial $Z_2$ topological order and gaps out the Bloch spectrum. A faithful mapping of the plasmonic system onto a tight-binding model is developed and shown to capture its essential topological signatures. Full wave numerical simulations of graphene disks arranged in a Lieb lattice confirm the existence of propagating helical boundary modes in the nontrivial band gap.

Growth of self-integrated atomic quantum wires and junctions of a Mott semiconductor. (arXiv:2305.12700v1 [cond-mat.mes-hall])
Tomoya Asaba, Lang Peng, Takahiro Ono, Satoru Akutagawa, Ibuki Tanaka, Hinako Murayama, Shota Suetsugu, Aleksandar Razpopov, Yuichi Kasahara, Takahito Terashima, Yuhki Kohsaka, Takasada Shibauchi, Masatoshi Ichikawa, Roser Valentí, Shin-ichi Sasa, Yuji Matsuda

Continued advances in quantum technologies rely on producing nanometer-scale wires. Although several state-of-the-art nanolithographic technologies and bottom-up synthesis processes have been used to engineer such wires, critical challenges remain in growing uniform atomic-scale crystalline wires and constructing their network structures. Here we discover a simple method to fabricate atomic-scale wires with various arrangements, including stripes, X-, Y-junctions, and nanorings. Single-crystalline atomic-scale wires of a Mott insulator, whose band gap is comparable to those of wide-gap semiconductors, are spontaneously grown on graphite substrates \DEL{and epitaxial monolayer graphene on SiC }by pulsed-laser deposition. These wires are one-unit-cell-thick and have an exact width of two- and four-unit-cells (1.4 and 2.8\,nm) and lengths up to a few $\mu m$. We show that the non-equilibrium reaction-diffusion processes may play an essential role in atomic pattern formation. Our findings offer a new perspective on the non-equilibrium self-organization phenomena on an atomic scale, paving a unique way for the quantum architecture of nano-network.

Enhancement of density of states and suppression of superconductivity in site-disordered topological metal LaPtSi. (arXiv:2305.12721v1 [cond-mat.supr-con])
Sitaram Ramakrishnan, Tatsuya Yamakawa, Ryohei Oishi, Yasuyuki Shimura, Takahiro Onimaru, Arumugam Thamizhavel, Srinivasan Ramakrishnan, Minoru Nohara

Single crystals of non-centrosymmetric $s$-wave superconductor LaPt$_{0.88}$Si$_{1.12}$ have been grown by the Czochralski (Cz) technique, whose crystal structure is described by the space group $I4{_1}md$ at ambient conditions. The inter-site mixing between platinum and silicon is confirmed by both single-crystal x-ray diffraction (SXRD) and electron probe micro-analyzer (EPMA). The disordered material exhibits a lower superconducting (SC) transition temperature $T_c$ at 2.02 K as opposed to the highest value of 3.9 K reported in polycrystalline LaPtSi without inter-site mixing. From specific heat, the Sommerfeld coefficient ($\gamma$) is estimated to be 7.85 mJ/mol K$^2$, which is much larger than the values reported for the samples exhibiting higher $T_c$. This is unprecedented as $T_c$ seems to decrease with increase in the electron density of states (DOS) at the Fermi energy and thus $\gamma$. The present work reports on the anomalous behaviour of SC and normal state properties of LaPt$_{x}$Si$_{2-x}$, presumably caused due to the existence of non-trivial topological bands.

Promoted Electronic Coupling of Acoustic Phonon Modes in Doped Semimetallic MoTe2. (arXiv:2305.12762v1 [cond-mat.supr-con])
Xiangyue Cui, Hejin Yan, Xuefei Yan, Kun Zhou, Yongqing Cai

As a prototype of the Weyl superconductor, layered molybdenum telluride (MoTe2) encompasses two semimetallic phases (1T_prime and Td) which differentiate from each other via a slight tilting of the out-of-plane lattice. Both phases are subjected to serious phase mixing which complicates the analysis of its origin of superconductivity. Herein, we explore the electron-phonon coupling (EPC) of the monolayer semimetallic MoTe2, without phase ambiguity under this thickness limit. Apart from the hardening or softening of phonon modes, the strength of the EPC can be strongly modulated by doping. Specifically, longitudinal and out-of-plane acoustic modes are significantly activated for electron doped MoTe2. This is ascribed to the presence of rich valley states and equispaced nesting bands which are dynamically populated under charge doping. Through comparing the monolayer and bilayer MoTe2, the strength of EPC is found to be less likely to depend on thickness for neutral samples but clearly promoted for thinner samples with electron doping, while for hole doping, the strength alters more significantly with the thickness than doping. Our work explains the puzzling issue of the doping sensitivity of the superconductivity in semimetallic MoTe2 and establishes the critical role of activating acoustic phonons in such low-dimensional materials.

Partial Hydrogenation of N-heteropentacene: Impact on molecular packing and electronic structure. (arXiv:2305.12791v1 [cond-mat.mtrl-sci])
Yutaro Ono, Ryohei Tsuruta, Tomohiro Nobeyama, Kazuki Matsui, Masahiro Sasaki, Makoto Tadokoro, Yasuo Nakayama, Yoichi Yamada

Four-nitrogen-containing 5,6,13,14-Tetraazapentacene (BTANC) has attracted attention as a new n-type organic semiconductor with a rigid crystalline phase due to intermolecular CH-N hydrogen bonding. However, in the thin film transistor of BTANC, poor carrier transport properties and low stability in the ambient condition have been reported so far; thus further refining and understanding of the thin film of BTANC will be required. Here, by means of carefully-controlled vacuum deposition of BTANC in the narrow window of temperature avoiding impurity sublimation and thermal degradation of molecules, we produced a well-defined monolayer on Cu(111) for molecular-level investigations. Synchrotron photoemission of the monolayer revealed a noticeable alteration of the chemical state of N atoms, which is unexpected for the pure BTANC molecule. In addition, molecular imaging of the monolayer by scanning tunneling microscope (STM) revealed that the molecular packing structure in the monolayer significantly differed from that in the single crystal of BTANC. These observations can be interpreted as a result of the partial hydrogenation of N atoms in BTANC and the emergence of the NH-N type intermolecular hydrogen bonding in the monolayer. These findings will provide a general remark and strategy to control the molecular packing structure and electronic property in the molecular films of the nitrogen-containing acenes, by means of controlled hydrogenation.

Thin Pyramidal Cones in Nematic Liquid Crystal. (arXiv:2305.12797v1 [cond-mat.soft])
Seyed Reza Seyednejad, Saeedeh Shoarinejad, Mohammad Reza Mozaffari, Faezeh Amini Joneghani

The present study investigates the arrangement of hollow pyramidal cone shells and their interactions with degenerate planar anchoring on the inner and outer surfaces of particles within the nematic host. The shell thickness is in order of the nematic coherence length. The numerical behavior of colloids is determined by minimizing the Landau-de Gennes free energy in the presence of the Fournier surface energy and using the finite element method. Colloidal pyramidal cones can orient parallel and perpendicular with the far director orientation. In the parallel alignment, we found the splay director distortion into the pyramid with two boojum defects at the inner and outer tips. The director shows bending distortion without defect patterns when the pyramid is aligned perpendicularly. They induce long-range dipolar interaction and can form nested structures in close contact.

Twirling and spontaneous symmetry breaking of domain wall networks in lattice-reconstructed heterostructures of 2D materials. (arXiv:2305.12848v1 [cond-mat.mes-hall])
M.A. Kaliteevsky, V.V. Enaldiev, V.I. Fal'ko

Lattice relaxation in twistronic bilayers with close lattice parameters and almost perfect crystallographic alignment of the layers results in the transformation of moir\'e pattern into a sequence of preferential stacking domains and domain wall networks. Here, we show that reconstructed moir\'e superlattices of the perfectly aligned heterobilayers of same-chalcogen transition metal dichalcogenides have broken-symmetry structures featuring twisted nodes ('twirls') of domain wall networks. Analysing twist-angle-dependences of strain characteristics for the broken-symmetry structures we show that the formation of twirl reduces amount of hydrostatic strain around the nodes, potentially, reducing their infuence on the band edge energies of electrons and holes.

Skyrmions and antiskyrmions in monoaxial chiral magnets. (arXiv:2305.13003v1 [cond-mat.mes-hall])
Vladyslav M. Kuchkin, Nikolai S. Kiselev

We show that competition between local interactions in monoaxial chiral magnets provides the stability of two-dimensional (2D) solitons with identical energies but opposite topological charges. These skyrmions and antiskyrmions represent metastable states in a wide range of parameters above the transition into the saturated ferromagnetic phase. The symmetry of the underlying micromagnetic functional gives rise to soliton zero modes allowing efficient control of their translational movement by the frequency of the circulating external magnetic field. We also discuss the role of demagnetizing fields in the energy balance between skyrmion and antiskyrmion and in their stability.

Lifetime of coexisting sub-10 nm zero-field skyrmions and antiskyrmions. (arXiv:2305.13018v1 [cond-mat.mtrl-sci])
Moritz A. Goerzen, Stephan von Malottki, Sebastian Meyer, Pavel F. Bessarab, Stefan Heinze

Magnetic skyrmions have raised high hopes for future spintronic devices. For many applications it would be of great advantage to have more than one metastable particle-like texture available. The coexistence of skyrmions and antiskyrmions has been proposed in inversion symmetric magnets with exchange frustration. However, so far only model systems have been studied and the lifetime of coexisting metastable topological spin structures has not been obtained. Here, we predict that skyrmions and antiskyrmions with diameters below 10 nm can coexist at zero magnetic field in a Rh/Co bilayer on the Ir(111) surface -- an experimentally feasible system. We show that the lifetimes of metastable skyrmions and antiskyrmions in the ferromagnetic ground state are above one hour for temperatures up to 75 K and 48 K, respectively. The entropic contribution to the nucleation and annihilation rates differs for skyrmions and antiskyrmions. This opens the route to thermally activated creation of coexisting skyrmions and antiskyrmions in frustrated magnets with Dzyaloshinskii-Moriya interaction.

Enhanced piezoelectric response at nanoscale vortex structures in ferroelectrics. (arXiv:2305.13096v1 [cond-mat.mtrl-sci])
Xiaowen Shi, Nimish Prashant Nazirkar, Ravi Kashikar, Dmitry Karpov, Shola Folarin, Zachary Barringer, Skye Williams, Boris Kiefer, Ross Harder, Wonsuk Cha, Ruihao Yuan, Zhen Liu, Dezhen Xue, Turab Lookman, Inna Ponomareva, Edwin Fohtung

The piezoelectric response is a measure of the sensitivity of a material's polarization to stress or its strain to an applied field. Using in-operando x-ray Bragg coherent diffraction imaging, we observe that topological vortices are the source of a five-fold enhancement of the piezoelectric response near the vortex core. The vortices form where several low symmetry ferroelectric phases and phase boundaries coalesce. Unlike bulk ferroelectric solid solutions in which a large piezoelectric response is associated with coexisting phases in the proximity of the triple point, the largest responses for pure BaTiO3 at the nanoscale are in spatial regions of extremely small spontaneous polarization at vortex cores. The response decays inversely with polarization away from the vortex, analogous to the behavior in bulk ceramics as the cation compositions are varied away from the triple point. We use first-principles-based molecular dynamics to augment our observations, and our results suggest that nanoscale piezoelectric materials with large piezoelectric response can be designed within a parameter space governed by vortex cores. Our findings have implications for the development of next-generation nanoscale piezoelectric materials.

Localization of chiral edge states by the non-Hermitian skin effect. (arXiv:2305.13139v1 [cond-mat.mes-hall])
Gui-Geng Liu, Subhaskar Mandal, Peiheng Zhou, Xiang Xi, Rimi Banerjee, Yuan-Hang Hu, Minggui Wei, Maoren Wang, Qiang Wang, Zhen Gao, Hongsheng Chen, Yihao Yang, Yidong Chong, Baile Zhang

Quantum Hall systems host chiral edge states extending along the one-dimensional boundary of any two-dimensional sample. In solid state materials, the edge states serve as perfectly robust transport channels that produce a quantised Hall conductance; due to their chirality, and the topological protection by the Chern number of the bulk bandstructure, they cannot be spatially localized by defects or disorder. Here, we show experimentally that the chiral edge states of a lossy quantum Hall system can be localized. In a gyromagnetic photonic crystal exhibiting the quantum Hall topological phase, an appropriately structured loss configuration imparts the edge states' complex energy spectrum with a feature known as point-gap winding. This intrinsically non-Hermitian topological invariant is distinct from the Chern number invariant of the bulk (which remains intact) and induces mode localization via the "non-Hermitian skin effect". The interplay of the two topological phenomena - the Chern number and point-gap winding - gives rise to a non-Hermitian generalisation of the paradigmatic Chern-type bulk-boundary correspondence principle. Compared to previous realisations of the non-Hermitian skin effect, the skin modes in this system have superior robustness against local defects and disorders.

Multi-scale lattice relaxation in chiral twisted trilayer graphenes. (arXiv:2305.13155v1 [cond-mat.mes-hall])
Naoto Nakatsuji, Takuto Kawakami, Mikito Koshino

We theoretically investigate the lattice relaxation and the electronic property in non-symemtric chiral TTGs by using an effective continuum model. The relaxed lattice structure forms a patchwork of moir\'e-of-moir\'e domains, where the moir\'e patterns given by layer 1 and 2, and layer 2 and 3 become locally commensurate with a specific relative alignment. The band calculation reveals a wide energy window (> 50 meV) with low density of states, featuring sparsely distributed highly one-dimensional electron bands. The wave function of these one-dimensional bands exhibits sharp localization at the boundaries between super-moir\'e domains. By calculating the Chern number of the local band structure within commensurate domains, the one-dimensional state is identified as a topological boundary state between distinct Chern insulators.

Vortex condensate and critical exponents in the $(2+1)$-dimensional $\mathrm{O}(2)$ model. (arXiv:2305.13156v1 [cond-mat.stat-mech])
A. Mariani

The vortex in the $(2+1)$-dimensional $\mathrm{O}(2)$ model is studied via numerical simulations in a fully non-perturbative lattice regularization. We compute the vortex condensate and susceptibility to determine its critical exponents and a renormalized condensate in the continuum limit. Together with recent results on the vortex mass, this gives a complete picture of the scaling behaviour of the vortex operator in this model and sheds light on the statistical mechanics of topological excitations.

Submolecular-scale control of phototautomerization. (arXiv:2305.13157v1 [cond-mat.mes-hall])
Anna Rosławska, Katharina Kaiser, Michelangelo Romeo, Eloïse Devaux, Fabrice Scheurer, Stéphane Berciaud, Tomáš Neuman, Guillaume Schull

Many natural and artificial reactions including photosynthesis or photopolymerization are initiated by stimulating organic molecules into an excited state, which enables new reaction paths. Controlling light-matter interaction can influence this key concept of photochemistry, however, it remained a challenge to apply this strategy to control photochemical reactions at the atomic scale. Here, we profit from the extreme confinement of the electromagnetic field at the apex of a scanning tunneling microscope (STM) tip to drive and control the rate of a free-base phthalocyanine phototautomerization with submolecular precision. By tuning the laser excitation wavelength and choosing the STM tip position, we control the phototautomerization rate and the relative tautomer population. This sub-molecular optical control can be used to study any other photochemical processes.

Observation of Quantum metric and non-Hermitian Berry curvature in a plasmonic lattice. (arXiv:2305.13174v1 [physics.optics])
Javier Cuerda, Jani M. Taskinen, Nicki Källman, Leo Grabitz, Päivi Törmä

We experimentally observe the quantum geometric tensor, namely the quantum metric and the Berry curvature, for a square lattice of radiatively coupled plasmonic nanoparticles. We observe a non-zero Berry curvature and show that it arises solely from non-Hermitian effects. The quantum metric is found to originate from a pseudospin-orbit coupling. The long-range nature of the radiative interaction renders the behavior distinct from tight-binding systems: Berry curvature and quantum metric are centered around high-symmetry lines of the Brillouin zone instead of high-symmetry points. Our results inspire new pathways in the design of topological systems by tailoring losses or gain.

Gibbs free energies via isobaric-isothermal flows. (arXiv:2305.13233v1 [physics.comp-ph])
Peter Wirnsberger, Borja Ibarz, George Papamakarios

We present a machine-learning model based on normalizing flows that is trained to sample from the isobaric-isothermal (NPT) ensemble. In our approach, we approximate the joint distribution of a fully-flexible triclinic simulation box and particle coordinates to achieve a desired internal pressure. We test our model on monatomic water in the cubic and hexagonal ice phases and find excellent agreement of Gibbs free energies and other observables compared with established baselines.

Entanglement Spectrum as a diagnostic of chirality of Topological Spin Liquids: Analysis of an $\mathrm{SU}(3)$ PEPS. (arXiv:2305.13240v1 [cond-mat.str-el])
Mark J. Arildsen, Ji-Yao Chen, Norbert Schuch, Andreas W. W. Ludwig

(2+1)-D chiral topological phases are often identified by studying low-lying entanglement spectra (ES) of their wavefunctions on long cylinders of finite circumference. For chiral topological states that possess global $\mathrm{SU}(3)$ symmetry, we can now understand, as shown in this work, the nature of the topological phase from the study of the splittings of degeneracies in the finite-size ES, at a given momentum, solely from the perspective of conformal field theory (CFT). This is a finer diagnostic than Li-Haldane "state-counting", extending the approach of PRB 106, 035138 (2022) by two of the authors. We contrast ES of such chiral topological states with those of a non-chiral PEPS (Kure\v{c}i\'c, Sterdyniak, and Schuch [PRB 99, 045116 (2019)]) also possessing $\mathrm{SU}(3)$ symmetry. That latter PEPS has the same discrete symmetry as the chiral PEPS: strong breaking of separate time-reversal and reflection symmetries, with invariance under the product of these two operations. However, the full analysis of the topological sectors of the ES of the latter PEPS in prior work [arXiv:2207.03246] shows lack of chirality, as would be manifested, e.g., by a vanishing chiral central charge. In the present work, we identify a distinct indicator and hallmark of chirality in the ES: the splittings of conjugate irreps. We prove that in the ES of the chiral states conjugate irreps are exactly degenerate, because the operators [related to the cubic Casimir invariant of $\mathrm{SU}(3)$] that would split them are forbidden. By contrast, in the ES of non-chiral states, conjugate splittings are demonstrably non-vanishing. Such a diagnostic significantly simplifies identification of non-chirality in low-energy finite-size ES for $\mathrm{SU}(3)$-symmetric topological states.

Pseudospin-orbit coupling and non-Hermitian effects in the Quantum Geometric Tensor of a plasmonic lattice. (arXiv:2305.13244v1 [physics.optics])
Javier Cuerda, Jani M. Taskinen, Nicki Källman, Leo Grabitz, Päivi Törmä

We theoretically predict the full quantum geometric tensor, comprising the quantum metric and the Berry curvature, for a square lattice of plasmonic nanoparticles. The gold nanoparticles act as dipole or multipole antenna radiatively coupled over long distances. The photonic-plasmonic eigenfunctions and energies of the system depend on momentum and polarization (pseudospin), and their topological properties are encoded in the quantum geometric tensor. By T-matrix numerical simulations, we identify a TE-TM band splitting at the diagonals of the first Brillouin zone, that is not predicted by the empty lattice band structure nor by the highly symmetric nature of the system. Further, we find quantum metric around these regions of the reciprocal space, and even a non-zero Berry curvature despite the trivial lattice geometry and absence of magnetic field. We show that this non-zero Berry curvature arises exclusively from non-Hermitian effects which break the time-reversal symmetry. The quantum metric, in contrast, originates from a pseudospin-orbit coupling given by the polarization and directional dependence of the radiation.

Scaling laws for planetary sediment transport from DEM-RANS numerical simulations. (arXiv:2203.00562v4 [astro-ph.EP] UPDATED)
Thomas Pähtz, Orencio Duŕan

We use an established discrete element method (DEM) Reynolds-averaged Navier--Stokes (RANS)-based numerical model to simulate non-suspended sediment transport across conditions encompassing almost seven orders of magnitude in the particle--fluid density ratio $s$, ranging from subaqueous transport ($s=2.65$) to aeolian transport in the highly rarefied atmosphere of Pluto ($s=10^7$), whereas previous DEM-based sediment transport studies did not exceed terrestrial aeolian conditions ($s\approx2000$). Guided by these simulations and by experiments, we semi-empirically derive simple scaling laws for the cessation threshold and rate of equilibrium aeolian transport, both exhibiting a rather unusual $s^{1/3}$-dependence. They constitute a simple means to make predictions of aeolian processes across a large range of planetary conditions. The derivation consists of a first-principle-based proof of the statement that, under relatively mild assumptions, the cessation threshold physics is controlled by only one dimensionless control parameter, rather than two expected from dimensional analysis. Crucially, unlike existing models, this proof does not resort to coarse-graining the particle phase of the aeolian transport layer above the bed surface. From the pool of existing models, only that by P\"ahtz et al. (\textit{J. Geophys. Res. Earth. Surf.}~126, e2020JF005859, 2021) is somewhat consistent with the combined numerical and experimental data. It captures the scaling of the cessation threshold and the $s^{1/3}$-dependence of the transport rate, but fails to capture the latter's superimposed grain size dependence. This hints at a lack of understanding of the transport rate physics and calls for future studies on this issue.

Observation of Fermi arcs and Weyl nodes in a non-centrosymmetric magnetic Weyl semimetal. (arXiv:2203.05440v2 [cond-mat.mes-hall] UPDATED)
Anup Pradhan Sakhya, Cheng-Yi Huang, Gyanendra Dhakal, Xue-Jian Gao, Sabin Regmi, Baokai Wang, Wei Wen, R. -H. He, Xiaohan Yao, Robert Smith, Milo Sprague, Shunye Gao, Bahadur Singh, Hsin Lin, Su-Yang Xu, Fazel Tafti, Arun Bansil, Madhab Neupane

Weyl semimetal (WSM), a novel state of quantum matter, hosts Weyl fermions as emergent quasiparticles resulting from the breaking of either inversion or time-reversal symmetry. Magnetic WSMs that arise from broken time-reversal symmetry provide an exceptional platform to understand the interplay between magnetic order and Weyl physics, but few WSMs have been realized. Here, we identify CeAlSi as a new non-centrosymmetric magnetic WSM via angle-resolved photoemission spectroscopy (ARPES) and first-principles, density-functional theory based calculations. Our surface-sensitive vacuum ultraviolet ARPES data confirms the presence of surface Fermi arcs as, the smoking gun evidence for the existence of the Weyl semimetallic state in CeAlSi. We also observe bulk Weyl cones in CeAlSi using bulk-sensitive soft-X-ray ARPES measurements. In addition, Ce 4f at bands are found near the Fermi level, indicating that CeAlSi is a unique platform for investigating exotic quantum phenomena resulting from the interaction of topology, magnetism and electronic correlations.

Complex electronic structure evolution of NdSb across the magnetic transition. (arXiv:2203.05879v2 [cond-mat.mtrl-sci] UPDATED)
Anup Pradhan Sakhya, Baokai Wang, Firoza Kabir, Cheng-Yi Huang, M. Mofazzel Hosen, Bahadur Singh, Sabin Regmi, Gyanendra Dhakal, Klauss Dimitri, Milo Sprague, Robert Smith, Eric D. Bauer, Filip Ronning, Arun Bansil, Madhab Neupane

The rare-earth monopnictide (REM) family, which hosts magnetic ground states with extreme magnetoresistance, has established itself as a fruitful playground for the discovery of interesting topological phases. Here, by using high-resolution angle-resolved photoemission spectroscopy complemented by first-principles density functional-theory based modeling, we examine the evolution of the electronic structure of the candidate REM Dirac semimetal NdSb across the magnetic transition. A complex angel-wing-like band structure near the zone center and three arc-like features at the zone corner have been observed. This dramatic reconstruction of the itinerant bands around the zone center is shown to be driven by the magnetic transition: Specifically,, the Nd 5d electron band backfolds at the Gamma point and hybridizes with the Sb 5p hole bands in the antiferromagnetic phase. Our study indicates that antiferromagnetism plays an intricate role in the electronic structure of the REM family.

Twisted-bilayer FeSe and the Fe-based superlattices. (arXiv:2208.11142v3 [cond-mat.str-el] UPDATED)
P. Myles Eugenio, Oskar Vafek

We derive BM-like continuum models for the bands of superlattice heterostructures formed out of Fe-chalcogenide monolayers: (${\bf\text I}$) a single monolayer experiencing an external periodic potential, and (${\bf\text II}$) twisted bilayers with long-range moire tunneling. A symmetry derivation for the inter-layer moire tunnelling is provided for both the $\Gamma$ and $M$ high-symmetry points. In this paper, we focus on moire bands formed from hole-band maxima centered on $\Gamma$, and show the possibility of moire bands with $C=0$ or $\pm 1$ topological quantum numbers without breaking time-reversal symmetry. In the $C=0$ region for $\theta\rightarrow 0$ (and similarly in the limit of large superlattice period for ${\bf\text I}$), the system becomes a square lattice of 2D harmonic oscillators. We fit our model to FeSe and argue that it is a viable platform for the simulation of the square Hubbard model with tunable interaction strength.

Probing enhanced electron-phonon coupling in graphene by infrared resonance Raman spectroscopy. (arXiv:2212.01342v2 [cond-mat.mes-hall] UPDATED)
Tommaso Venanzi, Lorenzo Graziotto, Francesco Macheda, Simone Sotgiu, Taoufiq Ouaj, Elena Stellino, Claudia Fasolato, Paolo Postorino, Vaidotas Mišeikis, Marvin Metzelaars, Paul Kögerler, Bernd Beschoten, Camilla Coletti, Stefano Roddaro, Matteo Calandra, Michele Ortolani, Christoph Stampfer, Francesco Mauri, Leonetta Baldassarre

We report on resonance Raman spectroscopy measurements with excitation photon energy down to 1.16 eV on graphene, to study how low-energy carriers interact with lattice vibrations. Thanks to the excitation energy close to the Dirac point at $\mathbf{K}$, we unveil a giant increase of the intensity ratio between the double-resonant 2D and 2D$^\prime$ peaks with respect to that measured in graphite. Comparing with fully \textit{ab initio} theoretical calculations, we conclude that the observation is explained by an enhanced, momentum-dependent coupling between electrons and Brillouin zone-boundary optical phonons. This finding applies to two dimensional Dirac systems and has important consequences for the modeling of transport in graphene devices operating at room temperature.

Bound states and controllable currents on Topological Insulator surfaces with extended magnetic defects. (arXiv:2212.04052v2 [cond-mat.mes-hall] UPDATED)
Eklavya Thareja, Ilya Vekhter

We show that a magnetic line defect on the surface of a topological insulator generically supports two distinct branches of spin-polarized and current carrying one-dimensional bound states. We identify the components of magnetic scattering that lead to the bound states. The velocity, and hence spin texture, of each of those branches can be independently tuned by a magnetic field rotated in the plane of the surface. We compute the local net and spin-resolved density of states as well as spin accumulation and charge currents. The net spin polarization and current due to both bound and scattering states vary stepwise as a function of the electrostatic and magnetic components of the scattering potential, and can be tuned by an applied field. We discuss stability of the bound states with respect to impurity scattering.

Structures and energies of computed silicon (001) small angle mixed grain boundaries as a function of three macroscopic characters. (arXiv:2212.14611v3 [cond-mat.mtrl-sci] UPDATED)
Wei Wan, Changxin Tang

Understanding how dislocation structures vary with grain boundary (GB) characters enables accurate controls of interfacial nano-patterns. In this atomistic study, we report the structure-property correlations of Si (001) small angle mixed grain boundaries (SAMGBs) under three macroscopic GB characters (tilt character, twist character, and an implicit rotation character between them). Firstly, the SAMGB energies are computed as a function of tilt angle, twist angle and rotation angle, based on which a revised Read-Shockley relationship capable of precisely describing the energy variations span the three-dimensional GB character space is fitted. Secondly, GB structural transitions from dislocation to amorphous structures are given as a function of tilt angle, twist angle and dislocation core radii. The proportion, topology and structural signatures of different SAMGB types defined from the ratio between the tilt and twist angles are also presented. Thirdly, by extracting the transformation of metastable SAMGB phases, the formation mechanisms of SAMGB structures are characterized as energetically favorable dislocation glide and reaction, from which the dislocation density function is derived. The relevant results about SAMGB energies and structures are validated and supported by theoretical calculations and experimental observations, respectively.

Effect of Impurities on Charge and Heat Transport in Tubular Nanowires. (arXiv:2302.02164v2 [cond-mat.mes-hall] UPDATED)
Hadi Rezaie Heris, Kristjan Ottar Klausen, Anna Sitek, Sigurdur Ingi Erlingsson, Andrei Manolescu

We calculate the charge and heat currents carried by electrons, originating from a temperature gradient and a chemical potential difference between the two ends of tubular nanowires with different geometries of the cross-sectional areas: circular, square, triangular, and hexagonal. We consider nanowires based on InAs semiconductor material, and use the Landauer-B\"{u}ttiker approach to calculate the transport quantities. We include impurities in the form of delta scatterers and compare their effect for different geometries. The results depend on the quantum localization of the electrons along the edges of the tubular prismatic shell. For example, the effect of impurities on the charge and heat transport is weaker in the triangular shell than in the hexagonal shell, and the thermoelectric current in the triangular case is several times larger than in the hexagonal case, for the same temperature gradient.

Flow patterns and defect dynamics of active nematics under an electric field. (arXiv:2302.08355v3 [cond-mat.soft] UPDATED)
Yutaka Kinoshita, Nariya Uchida

The effects of an electric field on the flow patterns and defect dynamics of two-dimensional active nematics are numerically investigated. We found that field-induced director reorientation causes anisotropic active turbulence characterized by enhanced flow perpendicular to the electric field. The average flow speed and its anisotropy are maximized at an intermediate field strength. Topological defects in the anisotropic active turbulence are localized and show characteristic dynamics {with simultaneous creation of} two pairs of defects. A laning state characterized by stripe domains with alternating flow directions is found at a larger field strength near the transition to the uniformly aligned state. We obtained periodic oscillations between the laning state and active turbulence, which resembles an experimental observation of active nematics subject to anisotropic friction.

Steric engineering of point defects in lead halide perovskites. (arXiv:2302.08412v2 [cond-mat.mtrl-sci] UPDATED)
Lucy D. Whalley

Due to their high photovoltaic efficiency and low-cost synthesis, lead halide perovskites have attracted wide interest for application in new solar cell technologies. The most stable and efficient ABX$_3$ perovskite solar cells employ mixed A-site cations, however the impact of cation mixing on carrier trapping and recombination -- key processes that limit photovoltaic performance -- is not fully understood. Here we analyse non-radiative carrier trapping in the mixed A-cation hybrid halide perovskite MA$_{1-x}$Cs$_x$PbI$_3$. By using rigorous first-principles simulations we show that cation mixing leads to a hole trapping rate at the iodine interstitial that is eight orders of magnitude greater than in the single cation system. We demonstrate that the same defect in the same material can display a wide variety of defect activity -- from electrically inactive to recombination centre -- and, in doing so, resolve conflicting reports in the literature. Finally, we propose a new mechanism in which steric effects can be used to determine the rate of carrier trapping; this is achieved by controlling the phase and dynamical response of the lattice through the A-site composition. Our findings elucidate crucial links between chemical composition, defect activity and optoelectronic performance, and suggest a general approach that can help to rationalise the development of new crystalline materials with target defect properties.

Topological metals constructed by sliding quantum wire arrays. (arXiv:2303.01990v2 [cond-mat.mes-hall] UPDATED)
Zheng-Wei Zuo, Linxi Lv, Dawei Kang

A general strategy of alternated slide construction to craft topological metals is proposed, where there is a relative slide between the odd and even chains in the trivial spinless quantum wire array. Firstly, taking the three-leg ladder as an example, we find that alternated slide can induce a topological phase transition from the normal metal to topological metal phases, which are protected by inversion symmetry. Remarkably, topological metal without nontrivial edge states is found, and the bulk-boundary correspondence breaks down. Secondly, the two-dimensional quantum wire arrays with alternated slide manifests similar physical behaviors. Two types of topological metal phases emerge, where there are gapless bulk bands with and without nontrivial edge states. These results could be confirmed by current experimental techniques.

Photogalvanic response in multi-Weyl semimetals. (arXiv:2303.12836v2 [cond-mat.mes-hall] UPDATED)
Arpit Raj, Swati Chaudhary, Gregory A. Fiete

We investigate the dependence of the photogalvanic response of a multi-Weyl semimetal on its topological charge, tilt, and chemical potential. We derive analytical expressions for the shift and injection conductivities for tilted charge-$n$ Weyl points $(n=1,2,3)$ using a low energy two-band effective Hamiltonian. For double-Weyl semimetals, we also compute the response from two-band and four-band tight-binding models with broken time-reversal symmetry to study the effect of band bending and the contributions from higher bands. We find a significant deviation in the responses obtained from the effective low-energy continuum model and more realistic four-band continuum and tight-binding models. We analyze several different limits of these models. We describe the nature of the deviations and provide estimates of their dependence on the frequency and other model parameters. Our analysis provides a simple explanation for the first-principle calculation based frequency dependence of the injection current in SrSi$_2$. Additionally, we find interesting parameter regimes where the frequency dependence of the non-linear optical response can be directly used to probe the type-I/type-II nature of the Weyl cone. We obtain analytical results for the charge-4 Weyl semimetal by reducing the original problem involving a triple $k$-space integral to one with only a double integral. This simplification allows us to extract all relevant information about the nature of its second-order dc response and the precise condition for observing circular photogalvanic effect quantization. The semi-analytical approach presented here can also be extended to a systematic study of second harmonic generation and first-order optical conductivity in charge-4 Weyl semimetals.

All-optical magnetization control in CrI$_3$ monolayers: a microscopic theory. (arXiv:2304.00331v2 [cond-mat.mes-hall] UPDATED)
A. Kudlis, M. Kazemi, Y. Zhumagulov, H. Schrautzer, P. F. Bessarab, I. V. Iorsh, I. A. Shelykh

Bright excitons in ferromagnetic monolayers CrI$_3$ efficiently interact with lattice magnetization, which makes possible all-optical resonant magnetization control in this material. Using the combination of ab-initio simulations within Bethe-Salpeter approach, semiconductor Bloch equations and Landau-Lifshitz equations, we construct a microscopic theory of this effect. Solving numerically the resulting system of the coupled equations describing the dynamics of atomic spins and spins of the excitons, we demonstrate the possibility of a tunable control of macroscopic magnetization of a sample.

Generalized Devil's staircase and RG flows. (arXiv:2304.07640v2 [cond-mat.stat-mech] UPDATED)
Ana Flack, Alexander Gorsky, Sergei Nechaev

We discuss a two-parameter renormalization group (RG) flow when parameters are organized in a single complex variable, $\tau$, with modular properties. Throughout the work we consider a special limit when the imaginary part of $\tau$ characterizing the disorder strength tends to zero. We argue that generalized Riemann-Thomae (gRT) function and the corresponding generalized Devil's staircase emerge naturally in a variety of physical models providing a universal behavior. In 1D we study the Anderson-like probe hopping in a weakly disordered lattice, recognize the origin of the gRT function in the spectral density of the probe and formulate specific RG procedure which gets mapped onto the discrete flow in the fundamental domain of the modular group $SL(2,Z)$. In 2D we consider the generalization of the phyllotaxis crystal model proposed by L. Levitov and suggest the explicit form of the effective potential for the probe particle propagating in the symmetric and asymmetric 2D lattice of defects. Analyzing the structure of RG flow equations in the vicinity of saddle points we claim emergence of BKT-like transitions at ${\rm Im}\,\tau\to 0$. We show that the RG-like dynamics in the fundamental domain of $SL(2,Z)$ for asymmetric lattices asymptotically approaches various ``metallic ratios'' (among which the ``Silver ratio'' is one of the examples). For a Hubbard model of particles on a ring interacting with long-ranged potentials we investigate the dependence of the ground state energy on the potential and demonstrate by combining numerical and analytical tools the emergence of the generalized Devil's staircase. Also we conjecture a bridge between a Hubbard model and a phyllotaxis.

Study of novel properties of graphene-ZnO heterojunction interface using density functional theory. (arXiv:2305.02798v2 [cond-mat.mtrl-sci] UPDATED)
H.D. Etea, K.N. Nigussa

Studies of the structural, electronic, and optical characteristics of the interfaces between graphene and ZnO polar surfaces is carried out using first-principles simulations. At the interface, a strong van der Waals force is present, and because of the different work functions of graphene and ZnO, charge transfer takes place. Graphene's superior conductivity is not impacted by its interaction with ZnO, since its Dirac point is unaffected despite its adsorption on ZnO. In hybrid systems, excited electrons with energies between 0 and 3 eV (above Fermi energy) are primarily accumulated on graphene. The calculations offer a theoretical justification for the successful operation of graphene / ZnO hybrid materials as photocatalysts and solar cells. ZnO semiconductor is found to be a suitable material with modest band gap, ($\sim$ 3 eV), having high transparency in visible region and a high optical conductivity.

Found 7 papers in prb
Date of feed: Tue, 23 May 2023 03:17:14 GMT

Search terms: (topolog[a-z]+)|(graphit[a-z]+)|(rhombohedr[a-z]+)|(graphe[a-z]+)|(chalcog[a-z]+)|(landau)|(weyl)|(dirac)|(STM)|(scan[a-z]+ tunne[a-z]+ micr[a-z]+)|(scan[a-z]+ tunne[a-z]+ spectr[a-z]+)|(scan[a-z]+ prob[a-z]+ micr[a-z]+)|(MoS.+\d+|MoS\d+)|(MoSe.+\d+|MoSe\d+)|(MoTe.+\d+|MoTe\d+)|(WS.+\d+|WS\d+)|(WSe.+\d+|WSe\d+)|(WTe.+\d+|WTe\d+)|(Bi\d+Rh\d+I\d+|Bi.+\d+.+Rh.+\d+.+I.+\d+.+)|(BiTeI)|(BiTeBr)|(BiTeCl)|(ZrTe5|ZrTe.+5)|(Pt2HgSe3|Pt.+2HgSe.+3)|(jacuting[a-z]+)

Thermodynamic properties on the homologous temperature scale from direct upsampling: Understanding electron-vibration coupling and thermal vacancies in bcc refractory metals
Axel Forslund, Jong Hyun Jung, Prashanth Srinivasan, and Blazej Grabowski
Author(s): Axel Forslund, Jong Hyun Jung, Prashanth Srinivasan, and Blazej Grabowski

We have calculated thermodynamic properties of four bcc refractory elements—V, Ta, Mo, and W—up to the melting point with full density-functional-theory accuracy, using the recently developed direct-upsampling method [J. H. Jung et al., npj Comput. Mater. 9, 3 (2023)]. The direct-upsampling methodo…

[Phys. Rev. B 107, 174309] Published Mon May 22, 2023

Highly mismatched antiferroelectric films: Transition order and mechanical state
Maria A. Kniazeva, Alexander E. Ganzha, Ran Gao, Arvind Dasgupta, Alexey V. Filimonov, and Roman G. Burkovsky
Author(s): Maria A. Kniazeva, Alexander E. Ganzha, Ran Gao, Arvind Dasgupta, Alexey V. Filimonov, and Roman G. Burkovsky

Epitaxial ${\mathrm{PbZrO}}_{3}/{\mathrm{SrRuO}}_{3}/{\mathrm{SrTiO}}_{3}$ heterostructures are among the most widely studied thin-film antiferroelectrics. This paper explores their temperature-induced phase transitions and the characteristics of the domain structure by means of high-resolution sync…

[Phys. Rev. B 107, 184113] Published Mon May 22, 2023

Optical activity and transport in twisted bilayer graphene: Spatial dispersion effects
S. Ta Ho and V. Nam Do
Author(s): S. Ta Ho and V. Nam Do

This study investigates the mechanisms driving optical activity and quantum transport in twisted bilayer graphene systems. We demonstrate that optical activity results from spatial dispersion, making it inadequate to consider the system purely two-dimensional. Therefore, we utilize the transfer matr…

[Phys. Rev. B 107, 195141] Published Mon May 22, 2023

Topological metals constructed by sliding quantum wire arrays
Zheng-Wei Zuo, Linxi Lv, and Dawei Kang
Author(s): Zheng-Wei Zuo, Linxi Lv, and Dawei Kang

A general strategy of alternated slide construction to craft topological metals is proposed, where there is a relative slide between the odd and even chains in the trivial spinless quantum wire array. Firstly, taking the three-leg ladder as an example, we find that alternated slide can induce a topo…

[Phys. Rev. B 107, 195142] Published Mon May 22, 2023

Efficient low-temperature simulations for fermionic reservoirs with the hierarchical equations  of motion method: Application to the Anderson impurity model
Xiaohan Dan, Meng Xu, J. T. Stockburger, J. Ankerhold, and Qiang Shi
Author(s): Xiaohan Dan, Meng Xu, J. T. Stockburger, J. Ankerhold, and Qiang Shi

The hierarchical equations of motion (HEOM) approach is an accurate method to simulate open system quantum dynamics, which allows for systematic convergence to numerically exact results. To represent effects of the bath, the reservoir correlation functions are usually decomposed into summation of mu…

[Phys. Rev. B 107, 195429] Published Mon May 22, 2023

Pressure-induced topological crystalline insulating phase in ${\mathrm{TlBiSe}}_{2}$: Experiments and theory
V. Rajaji, Raagya Arora, B. Joseph, Subhajit Roychowdhury, Umesh V. Waghmare, Kanishka Biswas, and Chandrabhas Narayana
Author(s): V. Rajaji, Raagya Arora, B. Joseph, Subhajit Roychowdhury, Umesh V. Waghmare, Kanishka Biswas, and Chandrabhas Narayana

We report in situ high-pressure studies on three-dimensional topological insulator ${\mathrm{TlBiSe}}_{2}$ using Raman scattering and synchrotron x-ray-diffraction experiments corroborated with the first-principles theoretical calculations. The phonon modes of a rhombohedral phase of ${\mathrm{TlBiS…

[Phys. Rev. B 107, 205139] Published Mon May 22, 2023

Large Rashba spin-orbit coupling and high-temperature quantum anomalous Hall effect in Re-intercalated $\text{graphene}/{\mathrm{CrI}}_{3}$ heterostructure
Yulei Han, Zhi Yan, Zeyu Li, Xiaohong Xu, Zhenyu Zhang, Qian Niu, and Zhenhua Qiao
Author(s): Yulei Han, Zhi Yan, Zeyu Li, Xiaohong Xu, Zhenyu Zhang, Qian Niu, and Zhenhua Qiao

In 2010, the quantum anomalous Hall effect (QAHE) in graphene was proposed in the presence of Rashba spin-orbit coupling and a ferromagnetic exchange field. After a decade of experimental exploration, the anomalous Hall conductance can only reach about 0.25 in units of $2{e}^{2}/h$, which was attrib…

[Phys. Rev. B 107, 205412] Published Mon May 22, 2023

Found 1 papers in prl
Date of feed: Tue, 23 May 2023 03:17:13 GMT

Search terms: (topolog[a-z]+)|(graphit[a-z]+)|(rhombohedr[a-z]+)|(graphe[a-z]+)|(chalcog[a-z]+)|(landau)|(weyl)|(dirac)|(STM)|(scan[a-z]+ tunne[a-z]+ micr[a-z]+)|(scan[a-z]+ tunne[a-z]+ spectr[a-z]+)|(scan[a-z]+ prob[a-z]+ micr[a-z]+)|(MoS.+\d+|MoS\d+)|(MoSe.+\d+|MoSe\d+)|(MoTe.+\d+|MoTe\d+)|(WS.+\d+|WS\d+)|(WSe.+\d+|WSe\d+)|(WTe.+\d+|WTe\d+)|(Bi\d+Rh\d+I\d+|Bi.+\d+.+Rh.+\d+.+I.+\d+.+)|(BiTeI)|(BiTeBr)|(BiTeCl)|(ZrTe5|ZrTe.+5)|(Pt2HgSe3|Pt.+2HgSe.+3)|(jacuting[a-z]+)

Telecom-Wavelength Quantum Repeater Node Based on a Trapped-Ion Processor
V. Krutyanskiy, M. Canteri, M. Meraner, J. Bate, V. Krcmarsky, J. Schupp, N. Sangouard, and B. P. Lanyon
Author(s): V. Krutyanskiy, M. Canteri, M. Meraner, J. Bate, V. Krcmarsky, J. Schupp, N. Sangouard, and B. P. Lanyon

A quantum repeater based on trapped ions allows the transmission of entangled, telecom-wavelength photons over 50 km.

[Phys. Rev. Lett. 130, 213601] Published Mon May 22, 2023

Found 1 papers in pr_res
Date of feed: Tue, 23 May 2023 03:17:11 GMT

Search terms: (topolog[a-z]+)|(graphit[a-z]+)|(rhombohedr[a-z]+)|(graphe[a-z]+)|(chalcog[a-z]+)|(landau)|(weyl)|(dirac)|(STM)|(scan[a-z]+ tunne[a-z]+ micr[a-z]+)|(scan[a-z]+ tunne[a-z]+ spectr[a-z]+)|(scan[a-z]+ prob[a-z]+ micr[a-z]+)|(MoS.+\d+|MoS\d+)|(MoSe.+\d+|MoSe\d+)|(MoTe.+\d+|MoTe\d+)|(WS.+\d+|WS\d+)|(WSe.+\d+|WSe\d+)|(WTe.+\d+|WTe\d+)|(Bi\d+Rh\d+I\d+|Bi.+\d+.+Rh.+\d+.+I.+\d+.+)|(BiTeI)|(BiTeBr)|(BiTeCl)|(ZrTe5|ZrTe.+5)|(Pt2HgSe3|Pt.+2HgSe.+3)|(jacuting[a-z]+)

Quantum spin Hall phase in GeSn heterostructures on silicon
B. M. Ferrari, F. Marcantonio, F. Murphy-Armando, M. Virgilio, and F. Pezzoli
Author(s): B. M. Ferrari, F. Marcantonio, F. Murphy-Armando, M. Virgilio, and F. Pezzoli

Topological phase transitions are predicted to emerge at the broken-gap junction between technologically relevant materials, namely thin epitaxial films of GeSn alloys deposited on Si. Robust theoretical methods are employed to demonstrate how strain and electric fields can be utilized to dynamically reconfigure these Si-compatible heterostructures into a quantum spin Hall insulator.

[Phys. Rev. Research 5, L022035] Published Mon May 22, 2023

Found 2 papers in nano-lett
Date of feed: Mon, 22 May 2023 20:31:38 GMT

Search terms: (topolog[a-z]+)|(graphit[a-z]+)|(rhombohedr[a-z]+)|(graphe[a-z]+)|(chalcog[a-z]+)|(landau)|(weyl)|(dirac)|(STM)|(scan[a-z]+ tunne[a-z]+ micr[a-z]+)|(scan[a-z]+ tunne[a-z]+ spectr[a-z]+)|(scan[a-z]+ prob[a-z]+ micr[a-z]+)|(MoS.+\d+|MoS\d+)|(MoSe.+\d+|MoSe\d+)|(MoTe.+\d+|MoTe\d+)|(WS.+\d+|WS\d+)|(WSe.+\d+|WSe\d+)|(WTe.+\d+|WTe\d+)|(Bi\d+Rh\d+I\d+|Bi.+\d+.+Rh.+\d+.+I.+\d+.+)|(BiTeI)|(BiTeBr)|(BiTeCl)|(ZrTe5|ZrTe.+5)|(Pt2HgSe3|Pt.+2HgSe.+3)|(jacuting[a-z]+)

[ASAP] Novel Topological Motifs and Superconductivity in Li-Cs System
Hong-Mei Huang, Qiang Zhu, Vladislav A. Blatov, Artem R. Oganov, Xiaoting Wei, Peng Jiang, and Yan-Ling Li

TOC Graphic

Nano Letters
DOI: 10.1021/acs.nanolett.3c00875

[ASAP] A Graphene-Based Straintronic Physically Unclonable Function
Subir Ghosh, Yikai Zheng, Shiva Subbulakshmi Radhakrishnan, Thomas F Schranghamer, and Saptarshi Das

TOC Graphic

Nano Letters
DOI: 10.1021/acs.nanolett.3c01145

Found 2 papers in nat-comm

Search terms: (topolog[a-z]+)|(graphit[a-z]+)|(rhombohedr[a-z]+)|(graphe[a-z]+)|(chalcog[a-z]+)|(landau)|(weyl)|(dirac)|(STM)|(scan[a-z]+ tunne[a-z]+ micr[a-z]+)|(scan[a-z]+ tunne[a-z]+ spectr[a-z]+)|(scan[a-z]+ prob[a-z]+ micr[a-z]+)|(MoS.+\d+|MoS\d+)|(MoSe.+\d+|MoSe\d+)|(MoTe.+\d+|MoTe\d+)|(WS.+\d+|WS\d+)|(WSe.+\d+|WSe\d+)|(WTe.+\d+|WTe\d+)|(Bi\d+Rh\d+I\d+|Bi.+\d+.+Rh.+\d+.+I.+\d+.+)|(BiTeI)|(BiTeBr)|(BiTeCl)|(ZrTe5|ZrTe.+5)|(Pt2HgSe3|Pt.+2HgSe.+3)|(jacuting[a-z]+)

Robust microscale structural superlubricity between graphite and nanostructured surface
< author missing >

Anion redox as a means to derive layered manganese oxychalcogenides with exotic intergrowth structures
< author missing >