Found 28 papers in cond-mat
Date of feed: Wed, 09 Aug 2023 00:30:00 GMT

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Business models to assure availability of advanced superconductors for the accelerator sector and promote stewardship of superconducting magnet technology for the US economy. (arXiv:2308.03808v1 [physics.acc-ph])
Lance Cooley, Kathleen Amm, Whitney Hischier, Steven Rotkoff, David Larbalestier

Stakeholders representing concerns of national and global leadership, industries that use superconducting magnets in products, manufacturers of superconducting wires and tapes that supply to industries, and innovation generators from small businesses and universities came together to address stewardship of superconducting magnet technology and assurance of supply of advanced superconductors to the accelerator sector. This report outlines potential public-private partnerships that develop and enhance domestic capabilities to meet the needs of science facilities in the accelerator systems sector and in the broader commercial ecosystem.

Honeycomb Layered Frameworks with Metallophilic Bilayers. (arXiv:2308.03809v1 [cond-mat.mtrl-sci])
Godwill Mbiti Kanyolo, Titus Masese, Yoshinobu Miyazaki, Shintaro Tachibana, Chengchao Zhong, Yuki Orikasa, Tomohiro Saito

Honeycomb layered frameworks with metallophilic bilayers have garnered traction in various disciplines due to their unique configuration and numerous physicochemical and topological properties, such as fast ionic conduction, coordination chemistry, and structural defects. These properties make them attractive for energy storage applications, leading to increased attention towards their metallophilic bilayer arrangements. This Review focuses on recent advancements in this field, including characterisation techniques like X-ray absorption spectroscopy and high-resolution transmission electron microscopy, particularly for silver-based oxides. It also highlights strategies related to cationic-deficient phases induced by topology or temperature, expanding the compositional space of honeycomb layered frameworks with a focus on cationic bilayer architectures. The Review further discusses theoretical approaches for understanding the bilayered structure, especially concerning critical phenomena at the monolayer-bilayer phase transition. Honeycomb layered frameworks are described as optimised lattices within the congruent sphere packing problem, equivalent to a specific two-dimensional conformal field theory. The monolayer-bilayer phase transition involves a 2D-to-3D crossover. Overall, this Review aims to provide a panoramic view of honeycomb layered frameworks with metallophilic bilayers and their potential applications in the emerging field of quantum matter. It is valuable for recent graduates and experts alike across diverse fields, extending beyond materials science and chemistry.

Edge states of 2D time-reversal-invariant topological superconductors with strong interactions and disorder: A view from the lattice. (arXiv:2308.03836v1 [cond-mat.str-el])
Jun Ho Son, Jason Alicea, Olexei I. Motrunich

Two-dimensional time-reversal-invariant topological superconductors host helical Majorana fermions at their boundary. We study the fate of these edge states under the combined influence of strong interactions and disorder, using the effective 1D lattice model for the edge introduced by Jones and Metlitski [Phys. Rev. B 104, 245130 (2021)]. We specifically develop a strong-disorder renormalization group analysis of the lattice model and identify a regime in which time-reversal is broken spontaneously, creating random magnetic domains; Majorana fermions localize to domain walls and form an infinite-randomness fixed point, identical to that appearing in the random transverse-field Ising model. While this infinite-randomness fixed point describes a fine-tuned critical point in a purely 1D system, in our edge context there is no obvious time-reversal-preserving perturbation that destabilizes the fixed point. Our analysis thus suggests that the infinite-randomness fixed point emerges as a stable phase on the edge of 2D topological superconductors when strong disorder and interactions are present.

Strongly Interacting Phases in Twisted Bilayer Graphene at the Magic Angle. (arXiv:2308.03843v1 [cond-mat.str-el])
Khagendra Adhikari, Kangjun Seo, K. S. D. Beach, Bruno Uchoa

Twisted bilayer graphene near the magic angle is known to have a cascade of insulating phases at integer filling factors of the low-energy bands. In this Letter we address the nature of these phases through an unrestricted, self-consistent Hartree-Fock calculation on the lattice that accounts for \emph{all} electronic bands. Using numerically unbiased methods, we show that Coulomb interactions screened only by metallic gates produce ferromagnetic insulating states at integer fillings $\nu\in[-4,4]$ with maximal spin polarization $M_{\text{FM}}=4-|\nu|$. With the exception of the $\nu=0,-2$ states, all other integer fillings have insulating phases with additional sublattice symmetry breaking and antiferromagnetism in the \emph{remote} bands. Valley polarization is found away from half filling. Odd filling factors $|\nu|=1,3$ have anomalous quantum Hall states with Chern number $|\mathcal{C}|=1$, whereas the $|\nu|=3$ states show strong particle-hole \emph{asymmetry} in the small-gap regime. We map the metal-insulator transitions of these phases as a function of the background dielectric constant.

Review on Infrared Nanospectroscopy of Natural 2D Phyllosilicates. (arXiv:2308.03860v1 [cond-mat.mes-hall])
Raphaela De Oliveira, Alisson R. Cadore, Raul O. Freitas, Ingrid D. Barcelos

Phyllosilicates emerge as a promising class of large bandgap lamellar insulators. Their applications have been explored from fabrication of graphene-based devices to 2D heterostructures based on transition metal dicalcogenides with enhanced optical and polaritonics properties. In this review, we provide an overview on the use of IR s-SNOM for studying nano-optics and local chemistry of a variety of 2D natural phyllosilicates. Finally, we bring a brief update on applications that combine natural lamellar minerals into multifunctional nanophotonic devices driven by electrical control.

Chirality manipulation of ultrafast phase switchings in a correlated CDW-Weyl semimetal. (arXiv:2308.03895v1 [cond-mat.str-el])
Bing Cheng, Di Cheng, Tao Jiang, Wei Xia, Boqun Song, Martin Mootz, Liang Luo, Ilias E. Perakis, Yongxin Yao, Yanfeng Guo, Jigang Wang

A recently emerging concept for quantum phase discovery is the controlled gapping of linear band crossings in topological semimetals. For example, achieving topological superconducting and charge-density-wave (CDW) gapping could introduce Majorana zero modes and axion electrodynamics, respectively. Light engineering of correlation gaps in topological materials provides a new avenue of achieving exotic topological phases inaccessible by conventional tuning methods such as doping and straining. Here we demonstrate a light control of correlation gaps and ultrafast phase switchings in a model CDW and polaron insulator (TaSe$_4$)$_2$I recently predicted to be an axion insulator. Our ultrafast terahertz photocurrent spectroscopy reveals a two-step, non-thermal melting of polarons and electronic CDW gap via studying the fluence dependence of a {\em longitudinal} circular photogalvanic current. The helicity-dependent photocurrent observed along the propagation of light reveals continuous ultrafast switchings from the polaronic state, to the CDW (axion) phase, and finally to a hidden Weyl phase as the pump fluence increases. Other distinguishing features corroborating with the light-induced switchings include: mode-selective coupling of coherent phonons to polaron and CDW modulation, and the emergence of a {\em non-thermal} chiral photocurrent above pump threshold of CDW-related phonons. The ultrafast chirality control of correlated topological states revealed here is important to realize axion electrodynamics and quantum computing.

Charge Polarization around Impurities in Strained Graphene. (arXiv:2308.03899v1 [cond-mat.mes-hall])
Mohamed M. Elsayed, Sang Wook Kim, Juan M. Vanegas, Valeri N. Kotov

Introducing quasiparticle anisotropy in graphene via uniaxial strain has a profound effect on the polarization charge density induced by external impurities, both Coulomb and short-range. In particular the charge distribution induced by a Coulomb impurity exhibits a power law tail modulated by a strain-dependent admixture of angular harmonics. The appearance of distributed charge is in sharp contrast to the response in pristine/isotropic graphene, where for subcritical impurities the polarization charge is fully localized at the impurity position. It is also interesting to note that our results are obtained strictly at zero chemical potential, and the behavior is fundamentally distinct from the typical Friedel oscillations observed at finite chemical potential. For weak to moderate strain, the $d$-wave symmetry is dominant. The presence of Dirac cone tilt, relevant to some 2D materials beyond graphene, can also substantially affect the induced charge distribution. Finally we consider impurities with short range potentials, and study the effect of strain on the charge response. Our results were obtained in the continuum via perturbation theory valid for weak (subcritical) potentials, and supported by numerical lattice simulations based on density functional theory.

Role of pressure in generation of intense velocity gradients in turbulent flows. (arXiv:2308.03902v1 [physics.flu-dyn])
Dhawal Buaria, Alain Pumir

We investigate the role of pressure, via its Hessian tensor $\mathbf{H}$, on amplification of vorticity and strain-rate and contrast it with other inviscid nonlinear mechanisms. Results are obtained from direct numerical simulations of isotropic turbulence with Taylor-scale Reynolds number in the range $140-1300$. Decomposing $\mathbf{H}$ into local isotropic ($\mathbf{H}^{\rm I}$) and nonlocal deviatoric ($\mathbf{H}^{\rm D}$) components reveals that $\mathbf{H}^{\rm I}$ depletes vortex stretching (VS), whereas $\mathbf{H}^{\rm D}$ enables it, with the former slightly stronger. The resulting inhibition is significantly weaker than the nonlinear mechanism which always enables VS. However, in regions of intense vorticity, identified using conditional statistics, contribution from $\mathbf{H}$ dominates over nonlinearity, leading to overall depletion of VS. We also observe near-perfect alignment between vorticity and the eigenvector of $\mathbf{H}$ corresponding to the smallest eigenvalue, which conforms with well-known vortex-tubes. We discuss the connection between this depletion, essentially due to (local) $\mathbf{H}^{\rm I}$, and recently identified self-attenuation mechanism [Buaria et al. {\em Nat. Commun.} 11:5852 (2020)], whereby intense vorticity is locally attenuated through inviscid effects. In contrast, the influence of $\mathbf{H}$ on strain-amplification is weak. It opposes strain self-amplification, together with VS, but its effect is much weaker than VS. Correspondingly, the eigenvectors of strain and $\mathbf{H}$ do not exhibit any strong alignments. For all results, the dependence on Reynolds number is very weak. In addition to the fundamental insights, our work provides useful data and validation benchmarks for future modeling endeavors, for instance in Lagrangian modeling of velocity gradient dynamics, where conditional $\mathbf{H}$ is explicitly modeled.

Mu-Metal Enhancement of Effects in Electromagnetic Fields Over Single Emitters Near Topological Insulators. (arXiv:2308.03932v1 [cond-mat.mes-hall])
Eitan Dvorquez, Benjamín Pavez, Qiang Sun, Felipe Pinto, Andrew D. Greentree, Brant C. Gibson, Jerónimo R. Maze

We focus on the transmission and reflection coefficients of light in systems involving of topological insulators (TI). Due to the electro-magnetic coupling in TIs, new mixing coefficients emerge leading to new components of the electromagnetic fields of propagating waves. We have discovered a simple heterostructure that provides a 100-fold enhancement of the mixing coefficients for TI materials. Such effect increases with the TI's wave impedance. We also predict a transverse deviation of the Poynting vector due to these mixed coefficients contributing to the radiative electromagnetic field of an electric dipole. Given an optimal configuration of the dipole-TI system, this deviation could amount to $0.18\%$ of the Poynting vector due to emission near not topological materials, making this effect detectable.

High Temperature Superconductivity with Strong Correlations and Disorder: Possible Relevance to Cu-doped Apatite. (arXiv:2308.03948v1 [cond-mat.supr-con])
Maciej Fidrysiak, Andrzej P. Kądzielawa, Józef Spałek

We examine the properties of topological strongly correlated superconductor with bond disorder on triangular lattice and demonstrate that our theoretical ($t$-$J$-$U$) model exhibits some unique features of the Cu-doped apatite $\mathrm{Pb_{10-\mathit{x}}Cu_\mathit{x}(PO_4)_{6}O}$. Namely, the paired state appears only for carrier concentration $0.8 \lesssim x < 1$ and is followed by a close-by phase separation into the superconducting and Mott insulating parts. Furthermore, a moderate amount of the bond disorder ($\Delta t / t \lesssim 20 \%$) does not alter essentially the topology with robust Chern number $C=2$ which diminishes beyond that limit. A room-temperature superconductivity is attainable only for the exchange to hopping ratio $J/|t| \ge 1$ if one takes the bare bandwidth suggested by current DFT calculations. The admixture of $s$-wave pairing component is induced by the disorder. The results have been obtained within statistically consistent variational approximation (SGA).

Perpendicular electronic transport and moir\'{e}-induced resonance in twisted interfaces of 3D graphite. (arXiv:2308.03993v1 [cond-mat.mes-hall])
Tenta Tani, Takuto Kawakami, Mikito Koshino

We calculate the perpendicular electrical conductivity in twisted three-dimensional graphite (rotationally-stacked graphite pieces) by using the effective continuum model and the recursive Green's function method. In the low twist angle regime $(\theta \lesssim 2^\circ)$, the conductivity shows a non-monotonous dependence with a peak and dip structure as a function of the twist angle. By analyzing the momentum-resolved conductance and the local density of states, this behavior is attributed to the Fano resonance between continuum states of bulk graphite and interface-localized states, which is a remnant of the flat band in the magic-angle twisted bilayer graphene. We also apply the formulation to the high-angle regime near the commensurate angle $\theta \approx 21.8^\circ$, and reproduce the conductance peak observed in the experiment.

Delocalized polaron and Burstein-Moss shift induced by Li in $\alpha$-$\textrm{V}_{2}\textrm{O}_{5}$: DFT+DMFT study. (arXiv:2308.04043v1 [cond-mat.str-el])
Huu T. Do, Alex Taekyung Lee, Hyowon Park, Anh Ngo

We performed density functional theory (DFT)+$U$ and dynamical mean field theory (DMFT) calculations with continuous time quantum Monte Carlo impurity solver to investigate the electronic properties of V$_2$O$_5$ and Li$_x$V$_2$O$_5$ ($x$ = 0.125 and 0.25). Pristine V$_2$O$_5$ is a charge-transfer insulator with strong O $p$-V $d$ hybridization, and exhibits a large band gap ($E_{\textrm{gap}}$) as well as non-zero conduction band (CB) gap. We show that the band gap, the number of $d$ electrons of vanadium, $N_d$, and conduction band (CB) gap for V$_2$O$_5$ obtained from our DMFT calculations are in excellent agreement with the experimental values. While the DFT+$U$ approach replicates the experimental band gap, it overestimates the value of $N_d$ and underestimates the CB gap. In the presence of low Li doping, the electronic properties of V$_2$O$_5$ are mainly driven by a polaronic mechanism, the electron spin resonance and electron nuclear double resonance spectroscopies observed the coexistence of free and bound polarons. Notably, our DMFT results identify both polaron types, with the bound polaron being energetically preferred, while DFT+$U$ method predicts only the free polaron. Our DMFT analysis also reveals that increased Li doping leads to electron filling in the conduction band, shifting the Fermi level, this result consistent with the observed Burstein-Moss shift upon enhanced Li doping and we thus demonstrate that the DFT+DMFT approach can be used for accurate and realistic description of strongly correlated materials.

Gold Nanoparticles Aggregation on Graphene Using Reactive Force Field: A Molecular Dynamic Study. (arXiv:2308.04089v1 [])
J. Hingies Monisha, V. Vasumathi, Prabal K Maiti

We examine the aggregation behavior of AuNPs of different sizes on graphene as function of temperature using molecular dynamic simulations with Reax Force Field (ReaxFF). In addition, the consequences of such aggregation on the morphology of AuNPs and the charge transfer behavior of AuNP-Graphene hybrid structure are analyzed. The aggregation of AuNPs on graphene is confirmed from the center of mass distance calculation. The simulation results indicate that the size of AuNPs and temperature significantly affect the aggregation behavior of AuNPs on graphene. The strain calculation showed that shape of AuNPs changes due to the aggregation and the smaller size AuNPs on graphene exhibit more shape changes than larger AuNPs at all the temperatures studies in this work. The charge transfer calculation reveals that, the magnitude of charge transfer is higher for larger AuNPs-graphene composite when compared with smaller AuNPs-graphene composite. The charge transfer trend and the trends seen in the number of Au atoms directly in touch with graphene are identical. Hence, our results conclude that, quantity of Au atoms directly in contact with graphene during aggregation is primarily facilitates charge transfer between AuNPs and graphene.

Designing optoelectronic properties by on-surface synthesis: formation and electronic structure of an iron-terpyridine macromolecular complex. (arXiv:2308.04105v1 [cond-mat.mtrl-sci])
Agustin Schiffrin, Martina Capsoni, Gelareh Farahi, Chen-Guang Wang, Cornelius Krull, Marina Castelli, Tanya S. Roussy, Katherine A. Cochrane, Yuefeng Yin, Nikhil Medhekar, Adam Q. Shaw, Wei Ji, Sarah A. Burke

Supramolecular chemistry protocols applied on surfaces offer compelling avenues for atomic scale control over organic-inorganic interface structures. In this approach, adsorbate-surface interactions and two-dimensional confinement can lead to morphologies and properties that differ dramatically from those achieved via conventional synthetic approaches. Here, we describe the bottom-up, on-surface synthesis of one-dimensional coordination nanostructures based on an iron (Fe)-terpyridine (tpy) interaction borrowed from functional metal-organic complexes used in photovoltaic and catalytic applications. Thermally activated diffusion of sequentially deposited ligands and metal atoms, and intra-ligand conformational changes, lead to Fe-tpy coordination and formation of these nanochains. Low-temperature Scanning Tunneling Microscopy and Density Functional Theory were used to elucidate the atomic-scale morphology of the system, providing evidence of a linear tri-Fe linkage between facing, coplanar tpy groups. Scanning Tunneling Spectroscopy reveals highest occupied orbitals with dominant contributions from states located at the Fe node, and ligand states that mostly contribute to the lowest unoccupied orbitals. This electronic structure yields potential for hosting photo-induced metal-to-ligand charge transfer in the visible/near-infrared. The formation of this unusual tpy/tri-Fe/tpy coordination motif has not been observed for wet chemistry synthesis methods, and is mediated by the bottom-up on-surface approach used here.

Optical Manipulation of the Charge Density Wave state in RbV3Sb5. (arXiv:2308.04128v1 [cond-mat.str-el])
Yuqing Xing, Seokjin Bae, Ethan Ritz, Fan Yang, Turan Birol, Andrea N. Capa Salinas, Brenden R. Ortiz, Stephen D. Wilson, Ziqiang Wang, Rafael M. Fernandes, Vidya Madhavan

Broken time-reversal symmetry in the absence of spin order indicates the presence of unusual phases such as orbital magnetism and loop currents. The recently discovered family of kagome superconductors AV$_3$Sb$_5$ (A = K, Rb, or Cs), hosting an exotic charge-density wave (CDW) state, has emerged as a strong candidate for this phase. While initial experiments suggested that the CDW phase breaks time-reversal symmetry, this idea is being intensely debated due to conflicting experimental data. In this work we use laser-coupled scanning tunneling microscopy (STM) to study RbV$_3$Sb$_5$. STM data shows that the Fourier intensities of all three CDW peaks are different, implying that the CDW breaks rotational and mirror symmetries. By applying linearly polarized light along high-symmetry directions, we show that the relative intensities of the CDW peaks can be reversibly switched, implying a substantial electro-striction response, indicative of strong non-linear electron-phonon coupling. A similar CDW intensity switching is observed with perpendicular magnetic fields, which implies an unusual piezo-magnetic response that, in turn, requires time-reversal symmetry-breaking. We show that the simplest CDW that satisfies these constraints and reconciles previous seemingly contradictory experimental data is an out-of-phase combination of bond charge order and loop currents that we dub congruent CDW flux phase. Our laser-STM data opens the door to the possibility of dynamic optical control of complex quantum phenomenon in correlated materials.

Electronic and magnetic properties of single chalcogen vacancies in MoS$_2$/Au(111). (arXiv:2308.04139v1 [cond-mat.mes-hall])
Sergey Trishin, Christian Lotze, Nils Krane, Katharina J. Franke

Two-dimensional (2D) transition-metal dichalcogenides (TMDC) are considered highly promising platforms for next-generation optoelectronic devices. Owing to its atomically thin structure, device performance is strongly impacted by a minute amount of defects. Although defects are usually considered to be disturbing, defect engineering has become an important strategy to control and design new properties of 2D materials. Here, we produce single S vacancies in a monolayer of MoS$_2$ on Au(111). Using a combination of scanning tunneling and atomic force microscopy, we show that these defects are negatively charged and give rise to a Kondo resonance, revealing the presence of an unpaired electron spin exchange coupled to the metal substrate. The strength of the exchange coupling depends on the density of states at the Fermi level, which is modulated by the moir\'e structure of the MoS$_2$ lattice and the Au(111) substrate. In the absence of direct hybridization of MoS$_2$ with the metal substrate, the S vacancy remains charge-neutral. Our results suggest that defect engineering may be used to induce and tune magnetic properties of otherwise non-magnetic materials.

Interplay of the complete-graph and Gaussian fixed-point asymptotics in finite-size scaling of percolation above the upper critical dimension. (arXiv:2308.04238v1 [cond-mat.stat-mech])
Mingzhong Lu, Sheng Fang, Zongzheng Zhou, Youjin Deng

Percolation has two mean-field theories, the Gaussian fixed point (GFP) and the Landau mean-field theory or the complete graph (CG) asymptotics. By large-scale Monte Carlo simulations, we systematically study the interplay of the GFP and CG effects to the finite-size scaling of percolation above the upper critical dimension $d_c = 6$ with periodic, free, and cylindrical boundary conditions. Our results suggest that, with periodic boundaries, the \emph{unwrapped} correlation length scales as $L^{d/6}$ at the critical point, diverging faster than $L$ above $d_c$. As a consequence, the scaling behaviours of macroscopic quantities with respect to the linear system size $L$ follow the CG asymptotics. The distance-dependent properties, such as the short-distance behaviour of the two-point correlation function and the Fourier transformed quantities with non-zero modes, are still controlled by the GFP. With free boundaries, since the correlation length is cutoff by $L$, the finite-size scaling at the critical point is controlled by the GFP. However, some quantities are observed to exhibit the CG aysmptotics at the low-temperature pseudo-critical point, such as the sizes of the two largest clusters. With cylindrical boundaries, due to the interplay of the GFP and CG effects, the correlation length along the axial direction of the cylinder scales as $\xi_L \sim L^{(d-1)/5}$ within the critical window of size $O(L^{-2(d-1)/5})$, distinct from both periodic and free boundaries. A field-theoretical calculation for deriving the scaling of $\xi_L$ is also presented. Moreover, the one-point surface correlation function along the axial direction of the cylinder is observed to scale as ${\tau}^{(1-d)/2}$ for short distance but then enter a plateau of order $L^{-3(d-1)/5}$ before it decays significantly fast.

Geometric Thermoelectric Pump: Energy Harvesting beyond Seebeck and Pyroelectric Effects. (arXiv:1402.3645v2 [cond-mat.mes-hall] UPDATED)
Jie Ren

Thermal-electric conversion is crucial for smart energy control and harvesting, such as thermal sensing and waste heat recovering. So far, people are aware of two main ways of direct thermal-electric conversion, Seebeck and pyroelectric effects, each with different working mechanisms, conditions and limitations. Here, we report the concept of "Geometric Thermoelectric Pump", as the third way of thermal-electric conversion beyond Seebeck and pyroelectric effects. In contrast to Seebeck effect that requires spatial temperature difference, Geometric Thermoelectric Pump converts the time-dependent ambient temperature fluctuation into electricity. Moreover, Geometric Thermoelectric Pump does not require polar materials but applies to general conducting systems, thus is also distinct from pyroelectric effect. We demonstrate that Geometric Thermoelectric Pump results from the temperature-fluctuation-induced charge redistribution, which has a deep connection to the topological geometric phase in non-Hermitian dynamics, as a consequence of the fundamental nonequilibrium thermodynamic geometry. The findings advance our understanding of geometric phase induced multiple-physics-coupled pump effect and provide new means of thermal-electric energy harvesting.

Strange metal phase of disordered magic-angle twisted bilayer graphene at low temperatures: from flatbands to weakly coupled Sachdev-Ye-Kitaev bundles. (arXiv:2205.09766v3 [cond-mat.dis-nn] UPDATED)
Chenan Wei, Tigran A. Sedrakyan

We use stochastic expansion and exact diagonalization to study the magic-angle twisted bilayer graphene (TBG) on a disordered substrate. We show that the substrate-induced strong Coulomb disorder in TBG with the chemical potential at the level of the flatbands drives the system to a network of weakly coupled Sachdev-Ye-Kitaev (SYK) bundles, stabilizing an emergent quantum chaotic strange metal (SM) phase of TBG that exhibits the absence of quasiparticles. The Gaussian orthogonal ensemble dominates TBG's long-time chaotic dynamics at strong disorder, whereas fast quantum scrambling appears in the short-time dynamics. In weak disorder, gapped phases of TBG exhibit exponentially decaying specific heat capacity and exponential decay in out-of-time-ordered correlators (OTOC). This is the system behavior in correlated insulator and superconducting phases, in agreement with the corresponding Larkin-Ovchinnikov result for correlators. The result suggests a low-temperature transition from the superconducting and correlated insulating phases into the strange metal upon increasing the disorder strength. We propose a finite-temperature phase diagram for Coulomb-disordered TBG and discuss the experimental consequences of the emergent SM phase.

Jordan-Wigner fermionization of quantum spin systems on arbitrary 2D lattices: A mutual Chern-Simons approach. (arXiv:2210.07718v2 [cond-mat.str-el] UPDATED)
Jagannath Das, Aman Kumar, Avijit Maity, Vikram Tripathi

A variety of analytical approaches have been developed for the study of quantum spin systems in two dimensions, the notable ones being spin-waves, slave boson/fermion parton constructions, and for lattices with one-to-one local correspondence of faces and vertices, the 2D Jordan-Wigner (JW) fermionization. Field-theoretically, JW fermionization is implemented through Chern-Simons (CS) flux attachment. For a correct fermionization of lattice quantum spin-$1/2$ magnets, it is necessary that the fermions obey mutual bosonic (anyonic) statistics under exchange - this is not possible to implement on arbitrary 2D lattices if fermionic matter couples only to the lattice gauge fields. Enlarging the gauge degrees of freedom to include the dual lattice allows the construction of consistent mutual Chern-Simons field theories. Here we propose a mutual CS theory where the microscopic (spin) degrees of freedom are represented as lattice fermionic matter additionally coupled to specific combinations of dual lattice gauge fields that depend on the local geometry. We illustrate the use of this method for understanding the properties of a honeycomb Kitaev model subjected to a strong Zeeman field in the $z$-direction. Our CS gauge theory framework provides an understanding why the topological phase is degraded at lower (higher) critical fields for the ferro- (antiferro-) magnetic Kitaev interaction. Additionally, we observe an effectively one-dimensional character of the low-excitations at higher fields in the $z$-direction which we also confirm by spin-wave calculations.

Appearance of Odd-Frequency Superconductivity in a Relativistic Scenario. (arXiv:2212.01849v3 [cond-mat.supr-con] UPDATED)
Patrick J. Wong, Alexander V. Balatsky

Odd-frequency superconductivity is an exotic superconducting state in which the symmetry of the gap function is odd in frequency. Here we show that an inherent odd-frequency mode emerges dynamically under application of a Lorentz transformation of the anomalous Green function with the general frequency-dependent gap function. To see this, we consider a Dirac model with quartic potential and perform a mean-field analysis to obtain a relativistic Bogoliubov-de Gennes system. Solving the resulting Gor'kov equations yields expressions for relativistic normal and anomalous Green functions. The form of the relativistically invariant pairing term is chosen such that it reduces to BCS form in the non-relativistic limit. We choose an ansatz for the gap function in a particular frame which is even-frequency and analyze the effects on the anomalous Green function under a boost into a relativistic frame. The odd-frequency pairing emerges dynamically as a result of the boost. In the boosted frame the order parameter contains terms which are both even and odd in frequency. The relativistic correction to the anomalous Green function to first order in the boost parameter is completely odd in frequency. This work provides evidence that odd-frequency pairing may form intrinsically within relativistic superconductors.

Multiscale simulations of growth-dominated Sb$_2$Te phase-change material for non-volatile photonic applications. (arXiv:2301.03146v2 [cond-mat.mtrl-sci] UPDATED)
Xu-Dong Wang, Wen Zhou, Hangming Zhang, Shehzad Ahmed, Tiankuo Huang, Riccardo Mazzarello, En Ma, Wei Zhang

Chalcogenide phase-change materials (PCMs) are widely applied in electronic and photonic applications, such as non-volatile memory and neuro-inspired computing. Doped Sb$_2$Te alloys are now gaining increasing attention for on-chip photonic applications, due to their growth-driven crystallization features. However, it remains unknown whether Sb$_2$Te also forms a metastable crystalline phase upon nanoseconds crystallization in devices, similar to the case of nucleation-driven Ge-Sb-Te alloys. Here, we carry out ab initio simulations to understand the changes in optical properties of amorphous Sb$_2$Te upon crystallization and post annealing. During the continuous transformation process, changes in the dielectric function are highly wavelength-dependent from the visible-light range towards the telecommunication band. Our finite-difference time-domain simulations based on the ab initio input reveal key differences in device output for color display and photonic memory applications upon tellurium ordering. Our work serves as an example of how multiscale simulations of materials can guide practical photonic phase-change applications.

Higher-order topological heat conduction on a lattice for detection of corner states. (arXiv:2303.08402v2 [cond-mat.mes-hall] UPDATED)
T. Fukui, T. Yoshida, Y. Hatsugai

A heat conduction equation on a lattice composed of nodes and bonds is formulated assuming the Fourier law and the energy conservation law. Based on this equation, we propose a higher-order topological heat conduction model on the breathing kagome lattice. We show that the temperature measurement at a conner node can detect the corner state which causes rapid heat conduction toward the heat bath, and that several-nodes measurement can determine the precise energy of the corner states.

Classification and emergence of quantum spin liquids in chiral Rydberg models. (arXiv:2303.12829v2 [cond-mat.str-el] UPDATED)
Poetri Sonya Tarabunga, Giuliano Giudici, Titas Chanda, Marcello Dalmonte

We investigate the nature of quantum phases arising in chiral interacting Hamiltonians recently realized in Rydberg atom arrays. We classify all possible fermionic chiral spin liquids with $\mathrm{U}(1)$ global symmetry using parton construction on the honeycomb lattice. The resulting classification includes six distinct classes of gapped quantum spin liquids: the corresponding variational wave functions obtained from two of these classes accurately describe the Rydberg many-body ground state at $1/2$ and $1/4$ particle density. Complementing this analysis with tensor network simulations, we conclude that both particle filling sectors host a spin liquid with the same topological order of a $\nu=1/2$ fractional quantum Hall effect. At density $1/2$, our results clarify the phase diagram of the model, while at density $1/4$, they provide an explicit construction of the ground state wave function with almost unit overlap with the microscopic one. These findings pave the way to the use of parton wave functions to guide the discovery of quantum spin liquids in chiral Rydberg models.

Fusion rules and shrinking rules of topological orders in five dimensions. (arXiv:2306.14611v2 [hep-th] UPDATED)
Yizhou Huang, Zhi-Feng Zhang, Peng Ye

As a series of work about 5D (spacetime) topological orders, here we employ the path-integral formalism of 5D topological quantum field theory (TQFT) established in Zhang and Ye, JHEP 04 (2022) 138 to explore non-Abelian fusion rules, hierarchical shrinking rules and quantum dimensions of particle-like, loop-like and membrane-like topological excitations in 5D topological orders. To illustrate, we focus on a prototypical example of twisted $BF$ theories that comprise the twisted topological terms of the $BBA$ type. First, we classify topological excitations by establishing equivalence classes among all gauge-invariant Wilson operators. Then, we compute fusion rules from the path-integral and find that fusion rules may be of non-Abelian nature, i.e., the fusion outcome can be a direct sum of distinct excitations. We further compute shrinking rules. Especially, we discover exotic hierarchical structures hidden in shrinking processes of 5D or higher: a membrane is shrunk into particles and loops, and the loops are subsequently shrunk into a direct sum of particles. We obtain the algebraic structure of shrinking coefficients and fusion coefficients. We compute the quantum dimensions of all excitations and find that sphere-like membranes and torus-like membranes differ not only by their shapes but also by their quantum dimensions. We further study the algebraic structure that determines anomaly-free conditions on fusion coefficients and shrinking coefficients. Besides $BBA$, we explore general properties of all twisted terms in $5$D. Together with braiding statistics reported before, the theoretical progress here paves the way toward characterizing and classifying topological orders in higher dimensions where topological excitations consist of both particles and spatially extended objects.

Continuum field theory of 3D topological orders with emergent fermions and braiding statistics. (arXiv:2307.09983v2 [cond-mat.str-el] UPDATED)
Zhi-Feng Zhang, Qing-Rui Wang, Peng Ye

Universal topological data of topologically ordered phases can be captured by topological quantum field theory in continuous space time by taking the limit of low energies and long wavelengths. While previous continuum field-theoretical studies of topological orders in $3$D real space focus on either self-statistics, braiding statistics, shrinking rules, fusion rules or quantum dimensions, it is yet to systematically put all topological data together in a unified continuum field-theoretical framework. Here, we construct the topological $BF$ field theory with twisted terms (e.g., $AAdA$ and $AAB$) as well as a $K$-matrix $BB$ term, in order to simultaneously explore all such topological data and reach anomaly-free topological orders. Following the spirit of the famous $K$-matrix Chern-Simons theory of $2$D topological orders, we present general formulas and systematically show how the $K$-matrix $BB$ term confines topological excitations, and how self-statistics of particles is transmuted between bosonic one and fermionic one. In order to reach anomaly-free topological orders, we explore, within the present continuum field-theoretical framework, how the principle of gauge invariance fundamentally influences possible realizations of topological data. More concretely, we present the topological actions of (i) particle-loop braidings with emergent fermions, (ii) multiloop braidings with emergent fermions, and (iii) Borromean-Rings braidings with emergent fermions, and calculate their universal topological data. Together with the previous efforts, our work paves the way toward a more systematic and complete continuum field-theoretical analysis of exotic topological properties of $3$D topological orders. Several interesting future directions are also discussed.

The correlated insulators of magic angle twisted bilayer graphene at zero and one quantum of magnetic flux: a tight-binding study. (arXiv:2308.01997v2 [cond-mat.mes-hall] UPDATED)
Miguel Sánchez Sánchez, Tobias Stauber

Magic angle twisted bilayer graphene (MATBG) has become one of the prominent topics in Condensed Matter during the last few years, however, fully atomistic studies of the interacting physics are missing. In this work, we study the correlated insulator states of MATBG in the setting of a tight-binding model, under a perpendicular magnetic field of $0$ and $26.5$ T, corresponding to zero and one quantum of magnetic flux per unit cell. At zero field and for dopings of two holes ($\nu=-2$) or two electrons ($\nu=+2$) per unit cell, the Kramers intervalley coherent (KIVC) order is the ground state at the Hartree-Fock level, although it is stabilized by a different mechanism to that in continuum model. At charge neutrality, the spin polarized state is competitive with the KIVC due to the on-site Hubbard energy. We obtain a strongly electron-hole asymmetric phase diagram with robust insulators for electron filling and metals for negative filling. In the presence of magnetic flux, we predict an insulator with Chern number $-2$ for $\nu=-2$, a spin polarized state at charge neutrality and competing insulators with Chern numbers $+2$ and $0$ at $\nu=+2$. The stability of the $\nu=+2$ insulators is determined by the screening environment, allowing for the possibility of observing a topological phase transition.

First-principle study of spin transport property in $L1_0$-FePd(001)/graphene heterojunction. (arXiv:2308.02171v2 [cond-mat.mtrl-sci] UPDATED)
Hayato Adachi, Ryuusuke Endo, Hikari Shinya, Hiroshi Naganuma, Mitsuharu Uemoto

In our previous work, we synthesized a metal/2D material heterointerface consisting of $L1_0$-ordered iron-palladium (FePd) and graphene (Gr) called FePd(001)/Gr. This system has been explored by both experimental measurements and theoretical calculations. In this study, we focus on a heterojunction composed of FePd and multilayer graphene referred to as FePd(001)/$m$-Gr/FePd(001), where $m$ represents the number of graphene layers. We perform first-principles calculations to predict their spin-dependent transport properties. The quantitative calculations of spin-resolved conductance and magnetoresistance (MR) ratio (150-200%) suggest that the proposed structure can function as a magnetic tunnel junction in spintronics applications. We also find that an increase in $m$ not only reduces conductance but also changes transport properties from the tunneling behavior to the graphite $\pi$-band-like behavior. Furthermore, we examine the impact of lateral displacements (sliding) at the interface and find that the spin transport properties remain robust despite these changes; this is the advantage of two-dimensional material hetero-interfaces over traditional insulating barrier layers such as MgO.

Found 4 papers in prb
Date of feed: Wed, 09 Aug 2023 03:17:06 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]+)

Structural anomaly and crystalline electric field excitations in low-dimensional ${\mathrm{KU}}_{2}{\mathrm{Te}}_{6}$
Mitchell M. Bordelon, Shannon S. Fender, S. M. Thomas, Joe D. Thompson, Eric D. Bauer, and Priscila F. S. Rosa
Author(s): Mitchell M. Bordelon, Shannon S. Fender, S. M. Thomas, Joe D. Thompson, Eric D. Bauer, and Priscila F. S. Rosa

Layered ternary actinide chalcogenides contain unique structural and magnetic properties that remain underexplored. ${\mathrm{KU}}_{2}{\mathrm{Te}}_{6}$ is a new member of the $A\text{−}R\text{−}Q$ ($A=$ alkali; $R=$ actinide; $Q=$ chalcogenide) materials family crystallizing in the $Cmcm$ space gro…

[Phys. Rev. B 108, 064406] Published Tue Aug 08, 2023

Disorder-dependent slopes of the upper critical field in nodal and nodeless superconductors
V. G. Kogan and R. Prozorov
Author(s): V. G. Kogan and R. Prozorov

We study the slopes of the upper critical field $S=∂{H}_{{}_{c2}}/∂T$ at the superconducting transition temperature ${T}_{c}$ in anisotropic superconductors with transport (nonmagnetic) scattering employing the Ginzburg-Landau theory, developed for this case by Pokrovsky and Pokrovsky [Phys. Rev. B

[Phys. Rev. B 108, 064502] Published Tue Aug 08, 2023

Electrostatic tuning of transmission in ${\mathrm{NbS}}_{2}/{\mathrm{WSe}}_{2}$ two-dimensional lateral heterostructures: A computational study
Poonam Kumari, Zahra Golsanamlou, Alexander Smogunov, Luca Sementa, and Alessandro Fortunelli
Author(s): Poonam Kumari, Zahra Golsanamlou, Alexander Smogunov, Luca Sementa, and Alessandro Fortunelli

We present a first-principles computational study of the ${\mathrm{NbS}}_{2}/{\mathrm{WSe}}_{2}$ junction between two transition metal dichalcogenide monolayers as a prototypical metal/semiconductor two-dimensional (2D) lateral heterostructure (LH) to investigate the effects of electrostatic perturb…

[Phys. Rev. B 108, 075404] Published Tue Aug 08, 2023

Interlayer interaction, shear vibrational mode, and tribological properties of two-dimensional bilayers with a commensurate moiré pattern
Alexander S. Minkin, Irina V. Lebedeva, Andrey M. Popov, Sergey A. Vyrko, Nikolai A. Poklonski, and Yurii E. Lozovik
Author(s): Alexander S. Minkin, Irina V. Lebedeva, Andrey M. Popov, Sergey A. Vyrko, Nikolai A. Poklonski, and Yurii E. Lozovik

The potential energy surface (PES) of the interlayer interaction of infinite twisted bilayer graphene is calculated for a set of commensurate moiré patterns using the registry-dependent Kolmogorov-Crespi empirical potential. The calculated PESs have the same shape for all considered moiré patterns, …

[Phys. Rev. B 108, 085411] Published Tue Aug 08, 2023

Found 2 papers in prl
Date of feed: Wed, 09 Aug 2023 03:17:07 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]+)

Generalized Thermalization in Quantum-Chaotic Quadratic Hamiltonians
Patrycja Łydżba, Marcin Mierzejewski, Marcos Rigol, and Lev Vidmar
Author(s): Patrycja Łydżba, Marcin Mierzejewski, Marcos Rigol, and Lev Vidmar

Thermalization (generalized thermalization) in nonintegrable (integrable) quantum systems requires two ingredients: equilibration and agreement with the predictions of the Gibbs (generalized Gibbs) ensemble. We prove that observables that exhibit eigenstate thermalization in single-particle sector e…

[Phys. Rev. Lett. 131, 060401] Published Tue Aug 08, 2023

Squeezed Superradiance Enables Robust Entanglement-Enhanced Metrology Even with Highly Imperfect Readout
Martin Koppenhöfer, Peter Groszkowski, and A. A. Clerk
Author(s): Martin Koppenhöfer, Peter Groszkowski, and A. A. Clerk

Quantum metrology protocols using entangled states of large spin ensembles attempt to achieve measurement sensitivities surpassing the standard quantum limit (SQL), but in many cases they are severely limited by even small amounts of technical noise associated with imperfect sensor readout. Amplific…

[Phys. Rev. Lett. 131, 060802] Published Tue Aug 08, 2023

Found 2 papers in pr_res
Date of feed: Wed, 09 Aug 2023 03:17:06 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]+)

Random networks with $q$-exponential degree distribution
Cesar I. N. Sampaio Filho, Marcio M. Bastos, Hans J. Herrmann, André A. Moreira, and José S. Andrade, Jr.
Author(s): Cesar I. N. Sampaio Filho, Marcio M. Bastos, Hans J. Herrmann, André A. Moreira, and José S. Andrade, Jr.

We use the configuration model to generate random networks having a degree distribution that follows a $q$-exponential, ${P}_{q}(k)=(2−q)λ{[1−(1−q)λk]}^{−1/(q−1)}$, for arbitrary values of the parameters $q$ and $λ$. Typically, for small values of $λ$, this distribution crosses over from a plateau a…

[Phys. Rev. Research 5, 033088] Published Tue Aug 08, 2023

Anatomy of dynamical quantum phase transitions
Maarten Van Damme, Jean-Yves Desaules, Zlatko Papić, and Jad C. Halimeh
Author(s): Maarten Van Damme, Jean-Yves Desaules, Zlatko Papić, and Jad C. Halimeh

Global quenches of quantum many-body models can give rise to periodic dynamical quantum phase transitions (DQPTs) directly connected to the zeros of a Landau order parameter (OP). The associated dynamics has been argued to bear a close resemblance to Rabi oscillations characteristic of two-level sys…

[Phys. Rev. Research 5, 033090] Published Tue Aug 08, 2023