Found 29 papers in cond-mat
Date of feed: Mon, 18 Sep 2023 00:30:00 GMT

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Deciphering the Enigma of Cu-Doped Lead Apatite (LK-99): Structural Insights, Electronic Properties, and Implications for Ambient-Pressure Superconductivity. (arXiv:2309.07928v1 [cond-mat.supr-con])
Jun Li, Qi An

The most recent discovery, the Cu-doped lead apatite LK-99, is a proposed room-temperature superconductor operating under ambient pressure. However, this discovery has brought a slew of conflicting results from different scientific groups. While some observed the absence of electrical resistance, others could not confirm any signs of superconductivity in LK-99. Here, we investigate the structural and electronic properties of LK-99 and its antecedent compounds through quantum mechanics (QM) and QM-based molecular dynamics (QM-MD) simulations. Our study elucidates the insulating nature of base compounds, Pb$_{10}$(PO$_4$)$_6$O and Pb$_{10}$(PO$_4$)$_6$(OH)$_2$, spotlighting their large band gaps. Notably, Cu doping in LK-99 disrupts its symmetry, yielding a distorted ground-state crystal structure with a triclinic P1 symmetry and CuO$_4$ square coordination. Such alterations predispose LK-99 to exhibit semiconducting behaviors, characterized by a flat band above the Fermi energy, arising from Cu-3d and O-2p orbitals. In addition, the S doping sustains the triclinic P1 symmetry but leads to a significantly reduced band gap, with a band emerging primarily from Cu-3d and S-3p orbitals. These findings are important in understanding LK-99's structural and electronic properties and provide a strategic compass for the development of high-T$_C$ superconductors.

Curved vortex surfaces in four-dimensional superfluids: II. Equal-frequency double rotations. (arXiv:2309.08016v1 [cond-mat.quant-gas])
Ben McCanna, Hannah M. Price

As is well-known, two-dimensional and three-dimensional superfluids under rotation can support topological excitations such as quantized point vortices and line vortices respectively. Recently, we have studied how, in a hypothetical four-dimensional (4D) superfluid, such excitations can be generalised to vortex planes and surfaces. In this paper, we continue our analysis of skewed and curved vortex surfaces based on the 4D Gross-Pitaevskii equation, and show that certain types of such states can be stabilised by equal-frequency double rotations for suitable parameters. This work extends the rich phenomenology of vortex surfaces in 4D, and raises interesting questions about vortex reconnections and the competition between various vortex structures which have no direct analogue in lower dimensions.

A substitutional quantum defect in WS$_2$ discovered by high-throughput computational screening and fabricated by site-selective STM manipulation. (arXiv:2309.08032v1 [cond-mat.mtrl-sci])
John C. Thomas, Wei Chen, Yihuang Xiong, Bradford A. Barker, Junze Zhou, Weiru Chen, Antonio Rossi, Nolan Kelly, Zhuohang Yu, Da Zhou, Shalini Kumari, Edward S. Barnard, Joshua A. Robinson, Mauricio Terrones, Adam Schwartzberg, D. Frank Ogletree, Eli Rotenberg, Marcus M. Noack, Sinéad Griffin, Archana Raja, David A. Strubbe, Gian-Marco Rignanese, Alexander Weber-Bargioni, Geoffroy Hautier

Point defects in two-dimensional materials are of key interest for quantum information science. However, the space of possible defects is immense, making the identification of high-performance quantum defects extremely challenging. Here, we perform high-throughput (HT) first-principles computational screening to search for promising quantum defects within WS$_2$, which present localized levels in the band gap that can lead to bright optical transitions in the visible or telecom regime. Our computed database spans more than 700 charged defects formed through substitution on the tungsten or sulfur site. We found that sulfur substitutions enable the most promising quantum defects. We computationally identify the neutral cobalt substitution to sulfur (Co$_{\rm S}^{0}$) as very promising and fabricate it with scanning tunneling microscopy (STM). The Co$_{\rm S}^{0}$ electronic structure measured by STM agrees with first principles and showcases an attractive new quantum defect. Our work shows how HT computational screening and novel defect synthesis routes can be combined to design new quantum defects.

Fermi surface and light quasi particles in hourglass nodal chain metal \b{eta}-ReO2. (arXiv:2309.08073v1 [cond-mat.str-el])
Daigorou Hirai, Takahito Anbai, Takako Konoike, Shinya Uji, Yuya Hattori, Taichi Terashima, Hajime Ishikawa, Koichi Kindo, Naoyuki Katayama, Tamio Oguchi, Zenji Hiroi

Quantum oscillations in magnetic torque and electrical resistivity were measured to investigate the electronic structure of \b{eta}-ReO2, a candidate hourglass nodal chain metal (Dirac loop chain metal). All the de Haas-van Alphen oscillation branches measured at 30 mK in magnetic fields of up to 17.5 T were consistent with first-principles calculations predicting four Fermi surfaces (FSs). The small-electron FS of the four FSs exhibited a very small cyclotron mass, 0.059 times that of the free electrons, which is likely to be related to the linear dispersion of the energy band. The consistency between the quantum oscillation results and band calculations indicates the presence of the hourglass nodal chain predicted for \b{eta}-ReO2 in the vicinity of the Fermi energy.

A facile direct device transfer of monolayer MoS2 towards improvement in transistor performances. (arXiv:2309.08205v1 [cond-mat.mes-hall])
Sameer Kumar Mallik, Roshan Padhan, Suman Roy, Mousam Charan Sahu, Sandhyarani Sahoo, Satyaprakash Sahoo

Transfer techniques based on two dimensional (2D) materials and devices offer immense potential towards their industrial integration with the existing silicon based electronics. To achieve high quality devices, there is an urgent requirement for the etching-free, and clean transfer that retain original semiconducting properties of layered channel materials. In parallel, transfer of metal electrode arrays on the 2D semiconductors also attract attention towards large-scale integration for commercial applications. Here, we demonstrate a facile PMMA-assisted etching-free one-step approach to transfer both 2D channels and metal electrodes without damaging the contact region. The direct device transfer (DDT) technique enables residue-free monolayer MoS2 as channel material towards achieving doping-free intrinsic transistors with enhanced performances. The crystalline quality, strain relaxation, and interfacial coupling effects are studied using Raman and photoluminescence spectra with spatial mapping. Post device transfer, a reduced pinning effect is observed by the effective modulation of gate tunable drain currents in MoS2 transistors at room temperature. Furthermore, the extracted Schottky barrier heights, temperature dependence of threshold voltage shifts, hysteresis evolution, and mobility enhancements validates the improved transistor performances in transferred devices. The proposed DDT method can be utilized to directly transfer array of devices of 2D materials and heterostructures skipping various cumbersome steps in between and hence could offer high performance reliable electronic applications.

Quantum Hall effect in topological Dirac semimetals modulated by the Lifshitz transition of the Fermi arc surface states. (arXiv:2309.08233v1 [cond-mat.str-el])
Tao-Rui Qin, Zhuo-Hua Chen, Tian-Xing Liu, Fu-Yang Chen, Hou-Jian Duan, Ming-Xun Deng, Rui-Qiang Wang

We investigate the magnetotransport of topological Dirac semimetals (DSMs) by taking into account the Lifshitz transition of the Fermi arc surface states. We demonstrate that a bulk momentum-dependent gap term, which is usually neglected in study of the bulk energy-band topology, can cause the Lifshitz transition by developing an additional Dirac cone for the surface to prevent the Fermi arcs from connecting the bulk Dirac points. As a result, the Weyl orbits can be turned off by the surface Dirac cone without destroying the bulk Dirac points. In response to the surface Lifshitz transition, the Weyl-orbit mechanism for the 3D quantum Hall effect (QHE) in topological DSMs will break down. The resulting quantized Hall plateaus can be thickness-dependent, similar to the Weyl-orbit mechanism, but their widths and quantized values become irregular. Accordingly, we propose that apart from the bulk Weyl nodes and Fermi arcs, the surface Lifshitz transition is also crucial for realizing stable Weyl orbits and 3D QHE in real materials.

Superconductivity and vortex structure on Bi$_{2}$Te$_{3}$/FeTe$_{0.55}$Se$_{0.45}$ heterostructures with different thickness of Bi$_{2}$Te$_{3}$ films. (arXiv:2309.08246v1 [cond-mat.supr-con])
Kailun Chen, Mingyang Chen, Chuanhao Wen, Zhiyong Hou, Huan Yang, Hai-Hu Wen

Using scanning tunnel microscopy (STM), we investigate the superconductivity and vortex properties in topological insulator Bi$_{2}$Te$_{3}$ thin films grown on the iron-based superconductor FeTe$_{0.55}$Se$_{0.45}$. The proximity-induced superconductivity weakens in the Bi$_{2}$Te$_{3}$ film when the thickness of the film increases. Unlike the elongated shape of vortex cores observed in the Bi$_{2}$Te$_{3}$ film with 2-quintuple-layer (QL) thickness, the isolated vortex cores exhibit a star shape with six rays in the 1-QL film, and the rays are along the crystalline axes of the film. This is consistent with the sixfold rotational symmetry of the film lattice, and the proximity-induced superconductivity is still topologically trivial in the 1-QL film. At a high magnetic field, when the direction between the two nearest neighbored vortices deviates from that of any crystalline axes, two cores connect each other by a pair of adjacent rays, forming a new type of electronic structure of vortex cores. On the 3-QL film, the vortex cores elongate along one of the crystalline axes of the Bi$_{2}$Te$_{3}$ film, similar to the results obtained on 2-QL films. The elongated vortex cores indicate a twofold symmetry of the superconducting gap induced by topological superconductivity with odd parity. This observation confirms possible topological superconductivity in heterostructures with a thickness of more than 2 QLs. Our results provide rich information for the vortex cores and vortex-bound states on the heterostructures consisting of the topological insulator and the iron-based superconductor.

Characterization of the Intrinsic and Extrinsic Resistances of a Microwave Graphene FET Under Zero Transconductance Conditions. (arXiv:2309.08282v1 [cond-mat.mes-hall])
Xiomara Ribero-Figueroa, Anibal Pacheco-Sanchez, Aida Mansouri, Pankaj Kumar, Omid Habibpour, Herbert Zirath, Roman Sordan, Francisco Pasadas, David Jiménez, Reydezel Torres-Torres

Graphene field-effect transistors exhibit negligible transconductance under two scenarios: for any gate-to-source voltage when the drain-to-source voltage is set to zero, and for an arbitrary drain-to-source voltage provided that the gate-to-source voltage equals the Dirac voltage. Hence, extracting the channel and the parasitic series resistances from S-parameters under these conditions enables analyzing their dependence on the gate and drain biases. This is fundamental to assess the portion of the output resistance that is controlled by the gate. Besides, the drain bias dependence of the drain and source resistances is also evidenced. Within the proposal, resistive components accounting for the lossy nature of the gate capacitance are incorporated into the model, which exhibits a broadband correlation with experimental data. This avoids the series resistances to be considered as frequency dependent in the model.

Quartz as an Accurate High-Field Low-Cost THz Helicity Detector. (arXiv:2309.08286v1 [physics.optics])
Maximilian Frenzel, Joanna M. Urban, Leona Nest, Tobias Kampfrath, Michael S. Spencer, Sebastian F. Maehrlein

The advent of high-field THz sources has opened the field of nonlinear THz physics and unlocked access to fundamental low energy excitations for ultrafast material control. Recent advances towards controlling and employing chiral excitations, or generally angular momentum of light, not only rely on the measurement of undistorted intense THz fields, but also on the precise knowledge about sophisticated THz helicity states. A recently reported and promising detector material is $\alpha$-quartz. However, its electrooptic response function and contributing nonlinear effects have remained elusive. Here, we establish z-cut $\alpha$-quartz as a precise electrooptic THz detector for full amplitude, phase and polarization measurement of intense THz fields, all at a fraction of costs of conventional THz detectors. We experimentally determine its complex detector response function, which is in good agreement with our model based on predominantly known literature values. It also explains previously observed thickness-dependent waveforms. These insights allow us to develop a swift and reliable protocol to precisely measure arbitrary THz polarization and helicity states. This two-dimensional electrooptic sampling (2D-EOS) in $\alpha$-quartz fosters rapid and cost-efficient THz time-domain ellipsometry, and enables the characterization of polarization-tailored fields for driving chiral or other helicity-sensitive quasiparticles and topologies.

Topological surface states host superconductivity induced by the bulk condensate in YRuB$_2$. (arXiv:2309.08308v1 [cond-mat.supr-con])
Nikhlesh Singh Mehta, Bikash Patra, Ghulam Mohmad, Mona Garg, Pooja Bhardwaj, P. K. Meena, K. Motla, Ravi Prakash Singh, Bahadur Singh, Goutam Sheet

While the possibility of topological superconductivity (TSC) in hybrid heterostructures involving topologically nontrivial band structure and superconductors has been proposed, the realization of TSC in a single stoichiometric material is most desired for fundamental experimental investigation of TSC and its device applications. Bulk measurements on YRuB$_2$ detect a single superconducting gap of $\sim$ 1 meV. This is supported by our electronic structure calculations which also reveal the existence of topological surface states in the system. We performed surface-sensitive Andreev reflection spectroscopy on YRuB$_2$ and detected the bulk superconducting gap as well as another superconducting gap of $\sim$ 0.5 meV. From our analysis of electronic structure, we show that the smaller gap is formed in the topological surface states in YRuB$_2$ due to the proximity of the bulk superconducting condensate. Thus, in agreement with the past theoretical predictions, we present YRuB$_2$ as a unique system that hosts superconducting topological surface states.

Chern-Simons-Modified-RPA-Eliashberg Theory of the nu=1/2+1/2 Quantum Hall Bilayer. (arXiv:2309.08329v1 [cond-mat.str-el])
Tevž Lotrič, Steven H. Simon

The nu=1/2+1/2 quantum Hall bilayer has been previsously modeled using Chern-Simons-RPA-Eliashberg (CSRPAE) theory to describe pairing between the two layers. However, these approaches are troubled by a number of divergences and ambiguities. By using a "modified" RPA approximation to account for mass renormalization, we can work in a limit where the cyclotron frequency is taken to infinity, effectively projecting to a single Landau level. This, surprisingly, controls the important divergences and removes ambiguities found in prior attempts at CSRPAE. Examining BCS pairing of composite fermions we find that the angular momentum channel l=+1 dominates for all distances d between layers and at all frequency scales. Examining BCS pairing of composite fermion electrons in one layer with composite fermion holes in the opposite layer, we find the l=0 pairing channel dominates for all d and all frequencies. The strength of the pairing in these two different descriptions of the same phase of matter is found to be almost identical. This agrees well with our understanding that these are two different but dual descriptions of the same phase of matter.

Phase Transformations and Energy Gap Variations in Uniaxial and Biaxial Strained Monolayer VS$_2$ TMDs: A Comprehensive DFT and Beyond-DFT Study. (arXiv:2309.08393v1 [cond-mat.mtrl-sci])
Oguzhan Orhan, Şener Özönder, Soner Ozgen

In the rapidly evolving field of 2D materials, transition metal dichalcogenides (TMDs) have emerged as compelling candidates for electronic applications. This study investigates the electronic structure of the H-phase monolayer VS$_2$ belonging to TMD family and the influence of strain on its band structure through Density Functional Theory (DFT). We employ two different pseudopotential approximations and a suite of computational methods including DFT+U, GAUPBE, G0W0, and self-GW to provide a nuanced understanding of its electronic band structure. A highlight of the study is its focus on how both uniaxial and biaxial strains, ranging from -5% to +5%, affect the electronic properties of the H-phase monolayer VS$_2$. Our comprehensive analysis reveals that these tensile strains significantly widen the energy gap, with uniaxial strains having a more pronounced effect than their biaxial counterparts. In addition, we identify an intriguing phase transition from a semiconducting to a metallic state under compressive strains, this transition is attributed to both symmetry breaking and bond length variation in the uniaxial case, the bond length in biaxial. These key findings not only enrich our understanding of the intricate electronic behavior of monolayer VS$_2$ under different strains but also pave the way for the design of innovative electronic devices using strain engineering.

Differences between quantum and classical adiabatic evolution. (arXiv:2309.08510v1 [cond-mat.mes-hall])
Cyrill Bösch, Andreas Fichtner, Marc Serra Garcia

Adiabatic evolution is an emergent design principle for time modulated metamaterials, often inspired by insights from topological quantum computing such as Majorana fermions and braiding operations. However, the pursuit of classical adiabatic metamaterials is rooted on the assumption that classical and quantum adiabatic evolution are equivalent. We show that this is not the case; and some instances of quantum adiabatic evolution, such as those containing zero modes, cannot be reproduced in classical systems. This is because mode coupling is fundamentally different in classical mechanics. We derive classical conditions to ensure adiabaticity and demonstrate that only under these, from quantum mechanics distinct conditions the Berry phase and Wilczek-Zee matrix emerge as meaningful quantities encoding the geometry of classical adiabatic evolution.

Exploiting ambipolarity in graphene field-effect transistors for novel designs on high-frequency analog electronics. (arXiv:2309.08519v1 [cond-mat.mes-hall])
Francisco Pasadas, Alberto Medina-Rull, Francisco G. Ruiz, Javier Noe Ramos-Silva, Anibal Pacheco-Sanchez, Mari Carmen Pardo, Alejandro Toral-Lopez, Andrés Godoy, Eloy Ramírez-García, David Jiménez, Enrique G. Marin

Exploiting ambipolar electrical conductivity based on graphene field-effect transistors has raised enormous interest for high-frequency (HF) analog electronics. Controlling the device polarity, by biasing the graphene transistor around the vertex of the V-shaped transfer curve, enables to redesign and highly simplify conventional analog circuits, and simultaneously to seek for multifunctionalities specially in the HF domain. We present, here, new insights for the design of different HF applications such as power amplifiers, mixers, frequency multipliers, phase shifters, and modulators that specifically leverage the inherent ambipolarity of graphene-based transistors.

Multi-orbital Kondo screening in strongly correlated polyradical nanographenes. (arXiv:2309.08524v1 [cond-mat.str-el])
Aitor Calvo-Fernández, Diego Soler-Polo, Andrés Pinar Solé, Shaotang Song, Oleksander Stetsovych, Manish Kumar, Guangwu Li, Jishan Wu, Jiong Lu, Asier Eiguren, María Blanco-Rey, Pavel Jelínek

We discuss coexistence of Kondo and spin excitation signals in tunneling spectroscopy in strongly correlated polyradical $\pi$-magnetic nanographenes on a metal surface. The Kondo signal is rationalized by a multi-orbital Kondo screening of the unpaired electrons. The fundamental processes are spin-flips of antiferromagnetic (AFM) order involving charged molecular multiplets. We introduce a~perturbative model, which provides simple rules to identify the presence of AFM channels responsible for Kondo screening. The Kondo regime is confirmed by numerical renormalization group calculations. This framework can be applied to similar strongly correlated open-shell systems.

Dynamical correlations and order in magic-angle twisted bilayer graphene. (arXiv:2309.08529v1 [cond-mat.str-el])
Gautam Rai, Lorenzo Crippa, Dumitru Călugăru, Haoyu Hu, Luca de' Medici, Antoine Georges, B. Andrei Bernevig, Roser Valentí, Giorgio Sangiovanni, Tim Wehling

In magic angle twisted bilayer graphene, transport, thermodynamic and spectroscopic experiments pinpoint at a competition between distinct low-energy states with and without electronic order, as well as a competition between localized and delocalized charge carriers. In this study, we utilize Dynamical Mean Field Theory (DMFT) on the topological heavy Fermion (THF) model of twisted bilayer graphene to investigate the emergence of electronic correlations and long-range order in the absence of strain. We explain the nature of emergent insulating and correlated metallic states, as well as transitions between them driven by three central phenomena: (i) the formation of local spin and valley isospin moments around 100K, (ii) the ordering of the local isospin moments around 10K, and (iii) a cascadic redistribution of charge between localized and delocalized electronic states upon doping. At integer fillings, we find that low energy spectral weight is depleted in the symmetric phase, while we find insulating states with gaps enhanced by exchange coupling in the zero-strain ordered phases. Doping away from integer filling results in distinct metallic states: a "bad metal" above the ordering temperature, where coherence of the low-energy electronic excitations is suppressed by scattering off the disordered local moments, and a "good metal" in the ordered states with coherence of quasiparticles facilitated by isospin order. Upon doping, there is charge transfer between the localized and delocalized orbitals of the THF model such that they get periodically filled and emptied in between integer fillings. This charge reshuffling manifests itself in cascades of doping-induced Lifshitz transitions, local spectral weight redistributions and periodic variations of the electronic compressibility ranging from nearly incompressible to negative.

Generalized Ginsparg-Wilson equations. (arXiv:2309.08542v1 [hep-lat])
Michael Clancy, David B. Kaplan, Hersh Singh

We give a general derivation of Ginsparg-Wilson relations for both Dirac and Majorana fermions in any dimension. These relations encode continuous and discrete chiral, parity and time reversal anomalies and will apply to the various classes of free fermion topological insulators and superconductors (in the framework of a relativistic quantum field theory in Euclidian spacetime). We show how to formulate the exact symmetries of the lattice action and the relevant index theorems for the anomalies.

Charge pumping with strong spin-orbit coupling: Fermi surface breathing and higher harmonic generation. (arXiv:2309.08597v1 [cond-mat.mes-hall])
A. Manchon, A. Pezo

Spin and charge pumping induced by a precessing magnetization has been instrumental to the development of spintronics. Nonetheless, most theoretical studies so far treat the spin-orbit coupling as a perturbation, which disregards the dynamical competition between exchange and spin-orbit fields. In this work, based on Keldysh formalism and Wigner expansion, we develop an adiabatic theory of spin and charge pumping adapted to multiorbital systems with arbitrary spin-orbit coupling. We apply this theory to the magnetic Rashba gas and magnetic graphene cases and discuss the pumped ac and dc current. We show that the pumped current possesses both intrinsic and extrinsic contributions, akin to the magnetic damping. In addition, we find that higher harmonics can be generated under large angle precession and we propose a couple of experimental setups where such an effect could be experimentally observed.

Long-lived Andreev states as evidence for protected hinge modes in a bismuth nanoring Josephson junction. (arXiv:2110.13539v2 [cond-mat.mes-hall] UPDATED)
A. Bernard, Y. Peng, A. Kasumov, R. Deblock, M. Ferrier, F. Fortuna, V. T. Volkov, Yu. A. Kasumov, Y. Oreg, F. von Oppen, H. Bouchiat, S. Gueron

Second-order topological insulators are characterized by helical, non-spin-degenerate, one-dimensional states running along opposite crystal hinges, with no backscattering. Injecting superconducting pairs therefore entails splitting Cooper pairs into two families of helical Andreev states of opposite helicity, one at each hinge. Here we provide evidence for such separation via the measurement and analysis of switching supercurrent statistics of a crystalline nanoring of bismuth. Using a phenomenological model of two helical Andreev hinge modes, we find that pairs relax at a rate comparable to individual quasiparticles, in contrast with the much faster pair relaxation of non-topological systems. This constitutes a unique tell-tale sign of the spatial separation of topological helical hinges.

A complementary screening for quantum spin Hall insulators in 2D exfoliable materials. (arXiv:2205.02583v3 [cond-mat.mes-hall] UPDATED)
Davide Grassano, Davide Campi, Antimo Marrazzo, Nicola Marzari

Quantum spin Hall insulators are a class of topological materials that has been extensively studied during the past decade. One of their distinctive features is the presence of a finite band gap in the bulk and gapless, topologically protected edge states that are spin-momentum locked. These materials are characterized by a $\mathbb{Z}_2$ topological order where, in the 2D case, a single topological invariant can be even or odd for a trivial or a topological material, respectively. Thanks to their interesting properties, such as the realization of dissipationless spin currents, spin pumping and spin filtering, they are of great interest in the field of electronics, spintronics and quantum computing. In this work we perform an high-throughput screening of Quantum spin Hall insulators starting from a set of 783 2D exfoliable materials, recently identified from a systematic screening of the ICSD, COD, and MPDS databases. We find a new $\mathbb{Z}_2$ topological insulator (HgNS) as well as 3 already known ones and 7 direect gap metals that have the potential of becoming Quantum spin Hall insulators under a reasonably weak external perturbation.

Differential current noise as an identifier of Andreev bound states that induce nearly quantized conductance plateaus. (arXiv:2301.06451v2 [cond-mat.mes-hall] UPDATED)
Zhan Cao, Gu Zhang, Hao Zhang, Ying-Xin Liang, Wan-Xiu He, Ke He, Dong E. Liu

Quantized conductance plateaus, a celebrated hallmark of Majorana bound states (MBSs) predicted a decade ago, have recently been observed with small deviations in iron-based superconductors and hybrid nanowires. Here, we demonstrate that nearly quantized conductance plateaus can also arise from trivial Andreev bound states (ABSs). To avoid ABS interruptions, we propose identifying ABS-induced quantized conductance plateaus by measuring the associated differential current noise $P$ versus bias voltage $V$. Specifically, for a quantized conductance plateau induced by one or multiple low-energy ABSs, the associated $P(V)$ curve exhibits a double-peak around zero bias, with the peak positions at $e|V|\approx 3k_B T$ (where $T$ is the temperature) and peak values larger than $2e^3/h$. These features greatly contrast those of an MBS or quasi-MBS, whose $P(V)$ curve displays a broad zero-bias dip and is consistently below $2e^3/h$. This protocol can be practically implemented in a variety of MBS candidate platforms using an electrode or STM tip as a probe.

Rare observation of spin-gapless semiconducting characteristics and related band topology of quaternary Heusler alloy CoFeMnSn. (arXiv:2303.08589v2 [cond-mat.str-el] UPDATED)
Shuvankar Gupta, Jyotirmoy Sau, Manoranjan Kumar, Chandan Mazumdar

In this paper, we report the theoretical investigation and experimental realization of a new spin-gapless semiconductor (SGSs) compound CoFeMnSn belonging to the family of quaternary Heusler alloys. Through the use of several ground-state energy calculations, the most stable structure has been identified. Calculations of the spin-polarized band structure in optimized structure's reveals the SGS nature of the compound. The compound form in an ordered crystal structure and exhibit a high ferromagnetic transition temperature (T$_{\rm C}$ = 560 K), making the material excellent for room temperature applications. Adherence of saturation magnetization to the Slater-Pauling rule, together with the nearly temperature-independent resistivity, conductivity, and carrier concentration of the compound in the temperature regime 5$-$300 K along with the low value of anomalous Hall conductivity (AHC) further confirms the SGS nature. Theoretical calculations also reveal the robustness of the SGS state due to lattice contraction and one can obtain a high value of intrinsic AHC using hole doping. Combined SGS and topological properties of the compound make CoFeMnSn suitable for spintronics and magneto-electronics devices.

Emergent metallicity at the grain boundaries of higher-order topological insulators. (arXiv:2304.15009v2 [cond-mat.mes-hall] UPDATED)
Daniel J. Salib, Vladimir Juričić, Bitan Roy

Topological lattice defects, such as dislocations and grain boundaries (GBs), are ubiquitously present in the bulk of quantum materials and externally tunable in metamaterials. In terms of robust modes, localized near the defect cores, they are instrumental in identifying topological crystals, featuring the hallmark band inversion at a finite momentum (translationally active type). Here we show that GB superlattices in both two-dimensional and three-dimensional translationally active higher-order topological insulators harbor a myriad of dispersive modes that are typically placed at finite energies, but always well-separated from the bulk states. However, when the Burgers vector of the constituting edge dislocations points toward the gapless corners or hinges, both second-order and third-order topological insulators accommodate self-organized emergent topological metals near the zero energy (half-filling) in the GB mini Brillouin zone. We discuss possible material platforms where our proposed scenarios can be realized through the band-structure and defect engineering.

Heat Conductance of the Quantum Hall Bulk. (arXiv:2306.14977v2 [cond-mat.mes-hall] UPDATED)
Ron Aharon Melcer, Avigail Gil, Arup-Kumar Paul, Priya Tiwary, Vladimir Umansky, Moty Heiblum, Yuval Oreg, Ady Stern, Erez Berg

The Quantum Hall Effect (QHE) is a prototypical realization of a topological state of matter. It emerges from a subtle interplay between topology, interactions, and disorder. The disorder enables the formation of localized states in the bulk that stabilize the quantum Hall states with respect to the magnetic field and carrier density. Still, the details of the localized states and their contribution to transport remain beyond the reach of most experimental techniques. Here, we describe an extensive study of the bulk's heat conductance. Using a novel 'multi-terminal' short device (on a scale of $10 \mu m$), we separate the longitudinal thermal conductance, $\kappa_{xx}T$ (due to bulk's contribution), from the topological transverse value $\kappa_{xy}T$, by eliminating the contribution of the edge modes. When the magnetic field is tuned away from the conductance plateau center, the localized states in the bulk conduct heat efficiently ($\kappa_{xx}T \propto T$), while the bulk remains electrically insulating. Fractional states in the first excited Landau level, such as the $\nu=7/3$ and $\nu=5/2$, conduct heat throughout the plateau with a finite $\kappa_{xx} T$. We propose a theoretical model that identifies the localized states as the cause of the finite heat conductance, agreeing qualitatively with our experimental findings.

Symmetry fractionalization, mixed-anomalies and dualities in quantum spin models with generalized symmetries. (arXiv:2307.01266v2 [cond-mat.str-el] UPDATED)
Heidar Moradi, Ömer M. Aksoy, Jens H. Bardarson, Apoorv Tiwari

We investigate the gauging of higher-form finite Abelian symmetries and their sub-groups in quantum spin models in spatial dimensions $d=2$ and 3. Doing so, we naturally uncover gauged models with dual higher-group symmetries and potential mixed 't Hooft anomalies. We demonstrate that the mixed anomalies manifest as the symmetry fractionalization of higher-form symmetries participating in the mixed anomaly. Gauging is realized as an isomorphism or duality between the bond algebras that generate the space of quantum spin models with the dual generalized symmetry structures. We explore the mapping of gapped phases under such gauging related dualities for 0-form and 1-form symmetries in spatial dimension $d=2$ and 3. In $d=2$, these include several non-trivial dualities between short-range entangled gapped phases with 0-form symmetries and 0-form symmetry enriched Higgs and (twisted) deconfined phases of the gauged theory with possible symmetry fractionalizations. Such dualities also imply strong constraints on several unconventional, i.e., deconfined or topological transitions. In $d=3$, among others, we find, dualities between topological orders via gauging of 1-form symmetries. Hamiltonians self-dual under gauging of 1-form symmetries host emergent non-invertible symmetries, realizing higher-categorical generalizations of the Tambara-Yamagami fusion category.

Raman spectroscopy of active-carbon electrodes when Au colloids are placed at the electrolyte/electrode interface. (arXiv:2307.05310v2 [cond-mat.mes-hall] UPDATED)
H. Grebel, Y. Zhang

We use surface enhanced Raman spectroscopy (SERS) in studying functionalized Au nanoparticles (AuNPs) when incorporated in active-carbon (A-C) based super-capacitor cells. We observe a resonance-like enhancement in the graphitic line (G-line) vs the D-line (defect line) of the A-C electrode. We also observed an enhancement in the specific capacitance of super-capacitor cell as a function of AuNPs concentration. All of these may be explained by the formation of a quasi-2D array of AuNPs at the interface between electrolyte and the electrode.

Topological Quantum Computation on a Chiral Kondo Chain. (arXiv:2309.03010v2 [cond-mat.str-el] UPDATED)
Tianhao Ren, Elio J. König, Alexei M. Tsvelik

We describe the chiral Kondo chain model based on the symplectic Kondo effect and demonstrate that it has a quantum critical ground state populated by non-Abelian anyons. We show that the fusion channel of two arbitrary anyons can be detected by locally coupling the two anyons to an extra single channel of chiral current and measuring the corresponding conductance at finite frequency. Based on such measurements, we propose that the chiral Kondo chain model with symplectic symmetry can be used for implementation of measurement-only topological quantum computations, and it possesses a number of distinct features favorable for such applications. The sources and effects of errors in the proposed system are analyzed, and possible material realizations are discussed.

Magnetized Baryonic layer and a novel BPS bound in the gauged-Non-Linear-Sigma-Model-Maxwell theory in (3+1)-dimensions through Hamilton-Jacobi equation. (arXiv:2309.03153v2 [hep-th] UPDATED)
Fabrizio Canfora

It is show that one can derive a novel BPS bound for the gauged Non-Linear-Sigma-Model (NLSM) Maxwell theory in (3+1) dimensions which can actually be saturated. Such novel bound is constructed using Hamilton-Jacobi equation from classical mechanics. The configurations saturating the bound represent Hadronic layers possessing both Baryonic charge and magnetic flux. However, unlike what happens in the more common situations, the topological charge which appears naturally in the BPS bound is a non-linear function of the Baryonic charge. This BPS bound can be saturated when the surface area of the layer is quantized. The far-reaching implications of these results are discussed. In particular, we determine the exact relation between the magnetic flux and the Baryonic charge as well as the critical value of the Baryonic chemical potential beyond which these configurations become thermodynamically unstable.

Floquet Nonadiabatic Nuclear Dynamics with Photoinduced Lorenz-Like Force in Quantum Transport. (arXiv:2308.12660v1 [quant-ph] CROSS LISTED)
Jingqi Chen, Wei Liu, Wenjie Dou

In our recent paper [Mosallanejad et al., Phys. Rev. B 107(18), 184314, 2023], we have derived a Floquet electronic friction model to describe nonadiabatic molecular dynamics near metal surfaces in the presence of periodic driving. In this work, we demonstrate that Floquet driving can introduce an anti-symmetric electronic friction tensor in quantum transport, resulting in circular motion of the nuclei in the long time limit. Furthermore, we show that such a Lorentz-like force strongly affects nuclear motion: at lower voltage bias, Floquet driving can increase the temperature of nuclei; at larger voltage bias, Floquet driving can decrease the temperature of nuclei. In addition, Floquet driving can affect electron transport strenuously. Finally, we show that there is an optimal frequency that maximizes electron current. We expect that the Floquet electronic friction model is a powerful tool to study nonadiabatic molecular dynamics near metal surfaces under Floquet driving in complex systems.

Found 8 papers in nano-lett
Date of feed: Sat, 16 Sep 2023 13:06:39 GMT

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[ASAP] ZrTe2 Compound Dirac Semimetal Contacts for High-Performance MoS2 Transistors
Xiaokun Wen, Wenyu Lei, Xinlu Li, Boyuan Di, Ye Zhou, Jia Zhang, Yuhui Zhang, Liufan Li, Haixin Chang, and Wenfeng Zhang

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Nano Letters
DOI: 10.1021/acs.nanolett.3c01554

[ASAP] Toroidal Dipole BIC-Driven Highly Robust Perfect Absorption with a Graphene-Loaded Metasurface
Rong Jin, Lujun Huang, Chaobiao Zhou, Jiaoyang Guo, Zhenchu Fu, Jian Chen, Jian Wang, Xin Li, Feilong Yu, Jin Chen, Zengyue Zhao, Xiaoshuang Chen, Wei Lu, and Guanhai Li

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Nano Letters
DOI: 10.1021/acs.nanolett.3c02958

[ASAP] Determining the Number of Graphene Nanoribbons in Dual-Gate Field-Effect Transistors
Jian Zhang, Gabriela Borin Barin, Roman Furrer, Cheng-Zhuo Du, Xiao-Ye Wang, Klaus Müllen, Pascal Ruffieux, Roman Fasel, Michel Calame, and Mickael L. Perrin

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Nano Letters
DOI: 10.1021/acs.nanolett.3c01931

[ASAP] Ultrafast Electronic Dynamics in Anisotropic Indirect Interlayer Excitonic States of Monolayer WSe2/ReS2 Heterojunctions
Yulu Qin, Rui Wang, Xiaoyuan Wu, Yunkun Wang, Xiaofang Li, Yunan Gao, Liangyou Peng, Qihuang Gong, and Yunquan Liu

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Nano Letters
DOI: 10.1021/acs.nanolett.3c02488

[ASAP] Kinetics of Nanobubbles in Tiny-Angle Twisted Bilayer Graphene
Chao Yan, Ya-Xin Zhao, Yi-Wen Liu, and Lin He

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Nano Letters
DOI: 10.1021/acs.nanolett.3c02286

[ASAP] Ultraflat Graphene Oxide Membranes with Newton-Ring Prepared by Vortex Shear Field for Ion Sieving
Tianqi Liu, Xin Zhang, Jing Liang, Wenbin Liang, Wei Qi, Longlong Tian, Lijuan Qian, Zhan Li, and Ximeng Chen

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Nano Letters
DOI: 10.1021/acs.nanolett.3c02613

[ASAP] Elastocaloric Effect in Graphene Kirigami
Luiz A. Ribeiro Junior, Marcelo L. Pereira Junior, and Alexandre F. Fonseca

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Nano Letters
DOI: 10.1021/acs.nanolett.3c02260

[ASAP] Spatially Coherent Tip-Enhanced Raman Spectroscopy Measurements of Electron–Phonon Interaction in a Graphene Device
Rafael Battistella Nadas, Andreij C. Gadelha, Tiago C. Barbosa, Cassiano Rabelo, Thiago de Lourenço e Vasconcelos, Vitor Monken, Ary V. R. Portes, Kenji Watanabe, Takashi Taniguchi, Jhonattan C. Ramirez, Leonardo C. Campos, Riichiro Saito, Luiz Gustavo Cançado, and Ado Jorio

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Nano Letters
DOI: 10.1021/acs.nanolett.3c00851