Found 27 papers in cond-mat
Date of feed: Fri, 09 Jun 2023 00:30:00 GMT

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Anderson Critical Metal Phase in Trivial States Protected by $C_{2z}T$ Symmetry on Average. (arXiv:2306.04683v1 [cond-mat.dis-nn])
Fa-Jie Wang, Zhen-Yu Xiao, Raquel Queiroz, B. Andrei Bernevig, Ady Stern, Zhi-Da Song

The joint symmetry $C_{2z}T$ protects obstructed atomic insulators in 2D translational invariant magnetic materials, where electrons form molecule orbitals with charge centers away from the positions of atoms. The transitions from these states to atomic insulators have to go through an intermediate metallic phase accomplished by the emergence, evolution, and annihilation of Dirac points. We show that, under (quenched) weak chemical potential disorder that respects the $C_{2z}T$ symmetry on average, the intermediate metallic phase remains delocalized, where every point in a finite transition process is a scale-invariant critical metal in the thermodynamic limit. We thus refer to the delocalized metallic phase as a crystalline-symmetry-associated critical metal phase. The underlying mechanism cannot be explained by conventional localization theories, such as weak anti-localization and topological phase transition in the ten-fold way classification. Through a quantitative mapping between lattice models and network models, we find that the critical metal phase is equivalent to a quantum percolation problem with random fluxes. The criticality can hence be understood through a semi-classical percolation theory.


Intrinsic antiferromagnetic multimeronic N\'eel spin-textures in ultrathin films. (arXiv:2306.04720v1 [cond-mat.mtrl-sci])
Amal Aldarawsheh, Moritz Sallermann, Muayad Abusaa, Samir Lounis

The realization of topological antiferromagnetic (AFM) solitons in real materials is a major goal towards their use in information technology. While they bear various advantages with respect to their ferromagnetic cousins, their observation is scarce. Utilizing first-principles simulations, here we predict new chiral particles in the realm of AFM topological magnetism, frustrated multimeronic spin-textures hosted by a N\'eel magnetic state, arising in single Mn layers directly grown on Ir(111) surface or interfaced with Pd-based films. These topological structures are intrinsic, i.e. they form in a single AFM material, can carry distinct topological charges and can combine in various multimeronic sequences with enhanced stability against external magnetic fields. We envision the frustrated N\'eel AFM multimerons as exciting highly-sought after AFM solitons having the potential to be utilized in novel spintronic devices hinging on non-synthetic AFM quantum materials.


Automatic graph representation algorithm for heterogeneous catalysis. (arXiv:2306.04742v1 [cond-mat.mtrl-sci])
Zachary Gariepy, ZhiWen Chen, Isaac Tamblyn, Chandra Veer Singh, Conrard Giresse Tetsassi Feugmo

One of the most appealing aspects of machine learning for material design is its high throughput exploration of chemical spaces, but to reach the ceiling of ML-aided exploration, more than current model architectures and processing algorithms are required. New architectures such as Graph Neural Networks (GNNs) have seen significant research investments recently. For heterogeneous catalysis, defining substrate intramolecular bonds and adsorbate/substrate intermolecular bonds is a time-consuming and challenging process. Before applying a model, dataset pre-processing, node/bond descriptor design, and specific model constraints have to be considered. In this work, a framework designed to solve these issues is presented in the form of an automatic graph representation algorithm (AGRA) tool to extract the local chemical environment of metallic surface adsorption sites is presented. This tool is able to gather multiple adsorption geometry datasets composed of different systems and combine them into a single model. To show AGRA's excellent transferability and reduced computational cost compared to other graph representation methods, it was applied to 5 different catalytic reaction datasets and benchmarked against the Open Catalyst Projects (OCP) graph representation method. The two ORR datasets with O/OH adsorbates obtained 0.053 eV RMSD when combined together, whereas the three CO2RR datasets with CHO/CO/COOH obtained an average performance of 0.088 eV RMSD. To further display the algorithm's versatility and extrapolation ability, a model was trained on a subset combination of all 5 datasets with an RMSD of 0.105 eV. This universal model was then used to predict a wide range of adsorption energies and an entirely new ORR catalyst system and then verified through Density Functional Theory calculations


The Performance of VQE across a phase transition point in the $J_1$-$J_2$ model on kagome lattice. (arXiv:2306.04851v1 [cond-mat.str-el])
Yuheng Guo, Mingpu Qin

Variational quantum eigensolver (VQE) is an efficient classical-quantum hybrid method to take advantage of quantum computers in the Noisy Intermediate-Scale Quantum (NISQ) era. In this work we test the performance of VQE by studying the $J_1$-$J_2$ anti-ferromagnetic Heisenberg model on the kagome lattice, which is found to display a first order phase transition at $J_2 / J_1 \approx 0.01$. By comparing the VQE states with the exact diagonalization results, we find VQE energies agree well with the exact values in most region of parameters for the 18-site system we studied. However, near the phase transition point, VQE tends to converge to the excited states when the number of variational parameters is not large enough. For the system studied in this work, this issue can be solved by either increasing the number of parameters or by initializing the parameters with converged values for $J_2/J_1$ away from the phase transition point. Our results provide useful guidance for the practical application of VQE on real quantum computers to study strongly correlated quantum many-body systems.


Non-coplanar helimagnetism in the layered van-der-Waals metal DyTe$_3$. (arXiv:2306.04854v1 [cond-mat.mtrl-sci])
Shun Akatsuka, Sebastian Esser, Shang Gao, Seno Aji, Yoshichika Onuki, Taka-hisa Arima, Taro Nakajima, Max Hirschberger

Magnetic materials with highly anisotropic chemical bonding can be exfoliated to realize ultrathin sheets or interfaces with highly controllable optical or spintronics responses, while also promising novel cross-correlation phenomena between electric polarization and the magnetic texture. The vast majority of these van-der-Waals magnets are collinear ferro-, ferri-, or antiferromagnets, with a particular scarcity of lattice-incommensurate helimagnets of defined left- or right-handed rotation sense, or helicity. Here we use polarized neutron scattering to reveal cycloidal, or conical, magnetic structures in DyTe$_3$, where insulating double-slabs of dysprosium square nets are separated by highly metallic tellurium layers. We identify a hierarchy of energy scales with -- in order of decreasing strength -- antiferromagnetic exchange interactions, magnetocrystalline anisotropy, and periodic modulations of the exchange energy. The latter are attributed to magneto-elastic coupling to the unconventional charge order in DyTe$_3$. This easily cleavable metallic helimagnet also hosts a complex magnetic phase diagram indicative of competing interactions. Our work paves the way for twistronics research, where helimagnetic layers can be combined to form complex spin textures on-demand, using the vast family of rare earth chalcogenides and beyond.


Three consecutive quantum anomalous Hall gaps in a metal-organic network. (arXiv:2306.04912v1 [cond-mat.str-el])
Xiang-Long Yu, Tengfei Cao, Rui Wang, Ya-Min Quan, Jiansheng Wu

In the quantum anomalous Hall (QAH) effect, chiral edge states are present in the absence of magnetic fields due to the intrinsic band topology. In this work, we predict that a synthesized two-dimensional metal-organic material, a Fe(biphenolate)$_3$ network, can be a unique QAH insulator, in which there are three consecutive nontrivial bandgaps. Based on first-principles calculations with effective model analysis, we reveal such nontrivial topology is from the $3$d$_{xz}$ and $3$d$_{yz}$ orbitals of Fe atoms. Moreover, we further study the effect of substrates, and the results shows that the metallic substrates used in the experiments (Ag and Cu) are unfavorable for observing the QAH effect whereas a hexagonal boron nitride substrate with a large bandgap may be a good candidate, where the three consecutive QAH gaps appear inside the substrate gap. The presence of three consecutive bandgaps near the Fermi level will significantly facilitate observations of the QAH effect in experiments.


Triplet State and Auger-Type Excitation Originating from Two-Electron Tunneling in Field Emission Resonance on Ag(100). (arXiv:2306.04916v1 [cond-mat.mes-hall])
Shin-Ming Lu, Ho-Hsiang Chang, Wei-Bin Su, Wen-Yuan Chan, Kung-Hsuan Lin, Chia-Seng Chang

In this study, we discovered that the energy gap above the vacuum level in the projected bulk band structure of Ag(100) prevents electrons in the first-order field emission resonance (FER) from inducing the surface plasmons. This mechanism allows light emission from FER to reveal characteristics of triplet states and Auger-type excitation resulting from two-electron tunneling in FER. According to optical spectra, surface plasmons can be induced by electrons in the zeroth-order FER. However, corresponding radiative decay can also trigger Auger-type excitation, whose energy state is influenced by the sharpness-dependent image potential acting on the scanning tunneling microscope tip.


Topological Superconducting States and Quasiparticle Transport on Kagome Lattice. (arXiv:2306.05034v1 [cond-mat.supr-con])
Zi-Qian Zhou, Weimin Wang, Zhi Wang, Dao-Xin Yao

The pairing symmetry of superconducting states is a critical topic in the realm of topological superconductivity. However, the pairing symmetry of the $\mathrm{AV_3Sb_5}$ family, wherein $\mathrm{A=K,Rb,Cs}$, remains indeterminate. To address this issue, we formulate an effective model on the kagome lattice to describe topological superconducting states featuring chiral charge density wave. Through this model, we explore the topological phase diagrams and thermal Hall conductivity under various parameters, with and without spin-orbit coupling. Our analysis reveals that the disparities in thermal Hall conductivity curves between different pairing symmetries are safeguarded by the topology resulting from the interplay of spin-orbital coupling and superconducting states. Remarkably, this theoretical prediction can potentially enable the differentiation of various superconducting pairing symmetries in materials via experimental measurements of thermal Hall conductivity curves.


Tunable magnon topology in monolayer CrI$_\mathbf{3}$ under external stimuli. (arXiv:2306.05104v1 [cond-mat.mes-hall])
M. Soenen, M. V. Milosevic

Two-dimensional (2D) honeycomb ferromagnets, such as monolayer chromium-trihalides, are predicted to behave as topological magnon insulators - characterized by an insulating bulk and topologically protected edge states, giving rise to a thermal magnon Hall effect. Here we report the behavior of the topological magnons in monolayer CrI$_3$ under external stimuli, including biaxial and uniaxial strain, electric gating, as well as in-plane and out-of-plane magnetic field, revealing that one can thereby tailor the magnetic states as well as the size and the topology of the magnonic bandgap. These findings broaden the perspective of using 2D magnetic materials to design topological magnonic devices.


Engineering flat bands in twisted-bilayer graphene away from the magic angle with chiral optical cavities. (arXiv:2306.05149v1 [cond-mat.mes-hall])
Cunyuan Jiang, Matteo Baggioli, Qing-Dong Jiang

Twisted bilayer graphene (TBG) is a recently discovered two-dimensional superlattice structure which exhibits strongly-correlated quantum many-body physics, including strange metallic behavior and unconventional superconductivity. Most of TBG exotic properties are connected to the emergence of a pair of isolated and topological flat electronic bands at the so-called magic angle, $\theta \approx 1.05^{\circ}$, which are nevertheless very fragile. In this work, we show that, by employing chiral optical cavities, the topological flat bands can be stabilized away from the magic angle in an interval of approximately $0.8^{\circ}<\theta<1.3^{\circ}$. As highlighted by a simplified theoretical model, time reversal symmetry breaking, induced by the chiral nature of the cavity, plays a fundamental role in flattening the isolated bands and gapping out the rest of the spectrum. The efficiency of the cavity is discussed as a function of the twisting angle, the light-matter coupling and the optical cavity characteristic frequency. Our results demonstrate the possibility of engineering flat bands in TBG using optical devices, extending the onset of strongly-correlated topological electronic phases in Moir\'e superlattices to a wider range in the twisting angle.


Solitons induced by an in-plane magnetic field in rhombohedral multilayer graphene. (arXiv:2306.05237v1 [cond-mat.mes-hall])
Max Tymczyszyn, Peter H. Cross, Edward McCann

We model the influence of an in-plane magnetic field on the orbital motion of electrons in rhombohedral graphene multilayers. For zero field, the low-energy band structure includes a pair of flat bands near zero energy which are localized on the surface layers of a finite thin film. For finite field, we find that the zero-energy bands persist and that level bifurcations occur at energies determined by the component of the in-plane wave vector $q$ that is parallel to the external field. The occurrence of level bifurcations is explained by invoking semiclassical quantization of the zero field Fermi surface of rhombohedral graphite. We find parameter regions with a single isoenergetic contour of Berry phase zero corresponding to a conventional Landau level spectrum and regions with two isoenergetic contours, each of Berry phase $\pi$, corresponding to a Dirac-like spectrum of levels. We write down an analogous one-dimensional tight-binding model and relate the persistence of the zero-energy bands in large magnetic fields to a soliton texture supporting zero-energy states in the Su-Schreiffer-Heeger model. We show that different states contributing to the zero-energy flat bands in rhombohedral graphene multilayers in a large field, as determined by the wave vector $q$, are localized on different bulk layers of the system, not just the surfaces.


Domain convexification: a simple model for invasion processes. (arXiv:2306.05273v1 [cond-mat.stat-mech])
David Martin-Calle, Olivier Pierre-Louis

We propose an invasion model where domains grow up to their convex hulls and merge when they overlap. This model can be seen as a continuum and isotropic counterpart of bootstrap percolation models. From numerical investigations of the model starting with randomly scattered discs in two dimensions, we find an invasion transition that occurs via macroscopic avalanches. The disc concentration threshold and the sharpness of the transition are found to decrease as the system size is increased. Our results are consistent with a vanishing threshold in the limit of infinitely large system sizes. However this limit could not be investigated by simulations. For finite initial concentrations of discs, the cluster size distribution presents a power-law tail characterized by an exponent that varies approximately linearly with the initial concentration of discs. These results at finite initial concentration open novel directions for the understanding of the transition in systems of finite size. Furthermore, we find that the domain area distribution has oscillations with discontinuities. In addition, the deviation from circularity of large domains is constant. Finally, we compare our results to experimental observations on de-adhesion of graphene induced by the intercalation of nanoparticles.


Spontaneous Self-Constraint in Active Nematic Flows. (arXiv:2306.05328v1 [cond-mat.soft])
Louise C. Head, Claire Dore, Ryan Keogh, Lasse Bonn, Amin Doostmohammadi, Kristian Thijssen, Teresa Lopez-Leon, Tyler N. Shendruk

Active processes drive and guide biological dynamics across scales -- from subcellular cytoskeletal remodelling, through tissue development in embryogenesis, to population-level bacterial colonies expansion. In each of these, biological functionality requires collective flows to occur while self-organized structures are protected; however, the mechanisms by which active flows can spontaneously constrain their dynamics to preserve structure have not previously been explained. By studying collective flows and defect dynamics in active nematic films, we demonstrate the existence of a self-constraint -- a two-way, spontaneously arising relationship between activity-driven isosurfaces of flow boundaries and mesoscale nematic structures. Our results show that self-motile defects are tightly constrained to viscometric surfaces -- contours along which vorticity and strain-rate balance. This in turn reveals that self-motile defects break mirror symmetry when they move along a single viscometric surface, in contrast with expectations. This is explained by an interdependence between viscometric surfaces and bend walls -- elongated narrow kinks in the orientation field. Although we focus on extensile nematic films, numerical results show the constraint holds whenever activity leads to motile half-charge defects. This mesoscale cross-field self-constraint offers a new framework for tackling complex 3D active turbulence, designing dynamic control into biomimetic materials, and understanding how biological systems can employ active stress for dynamic self-organization.


Olympicene radicals as building blocks of two-dimensional anisotropic networks. (arXiv:2306.05346v1 [cond-mat.mes-hall])
Ricardo Ortiz

I propose monoradical nanographenes without C3 symmetry as building blocks to design two-dimensional (2D) carbon crystals. As representative examples I study the honeycomb and Kagome lattices, showing that by replacing the sites with olympicene radicals the band dispersion near the Fermi energy corresponds, respectively, to that of Kekul\'e/anti-Kekul\'e graphene and breathing Kagome tight-binding models. As a consequence, finite islands of these new crystals present corner states close to the Fermi energy, just like the parent models. In the case of Kekul\'e/anti-Kekul\'e graphene, such states are topologically protected, standing as examples of second-order topological insulators with a non-zero Z2- or Z6-Berry phase. Differently, those of the breathing Kagome lattice are of trivial nature, but the ground state has been predicted to be a spin liquid in the antiferromagnetic Heisenberg model. Hence, 2D systems made of low-symmetric nanographenes may be convenient platforms to explore exotic physics in carbon materials.


Electroluminescence of the graphene 2D semi-metal. (arXiv:2306.05351v1 [cond-mat.mes-hall])
A. Schmitt, L. Abou-Hamdan, M. Tharrault, S. Rossetti, D. Mele, R. Bretel, A. Pierret, M. Rosticher, P. Morfin, T. Taniguchi, K. Watanabe, J.M. Berroir, G. Fève, G. Ménard, B. Plaçais, C. Voisin, J.P. Hugonin, J.J. Greffet, P. Bouchon, Y. De Wilde, E. Baudin

Electroluminescence, a non-thermal radiative process, is ubiquitous in semi-conductors and insulators but fundamentally precluded in metals. We show here that this restriction can be circumvented in high-quality graphene. By investigating the radiative emission of semi-metallic graphene field-effect transistors over a broad spectral range, spanning the near- and mid-infrared, we demonstrate direct far-field electroluminescence from hBN-encapsulated graphene in the mid-infrared under large bias in ambient conditions. Through a series of test experiments ruling out its incandescence origin, we determine that the electroluminescent signal results from the electrical pumping produced by interband tunneling. We show that the mid-infrared electroluminescence is spectrally shaped by a natural quarter-wave resonance of the heterostructure. This work invites a reassessment of the use of metals and semi-metals as non-equilibrium light emitters, and the exploration of their intriguing specificities in terms of carrier injection and relaxation, as well as emission tunability and switching speed.


Longitudinal and spin/valley Hall optical conductivity in single layer $MoS_{2}$. (arXiv:1211.3094v2 [cond-mat.mes-hall] UPDATED)
Zhou Li, J. P. Carbotte

A monolayer of $MoS_{2}$ has a non-centrosymmetric crystal structure, with spin polarized bands. It is a two valley semiconductor with direct gap falling in the visible range of the electromagnetic spectrum. Its optical properties are of particular interest in relation to valleytronics and possible device applications. We study the longitudinal and the transverse Hall dynamical conductivity which is decomposed into charge, spin and valley contributions. Circular polarized light associated with each of the two valleys separately is considered and results are filtered according to spin polarization. Temperature can greatly change the spin admixture seen in the frequency window where they are not closely in balance.


Overheated Topological Hall Effect. (arXiv:1812.09847v7 [cond-mat.mtrl-sci] UPDATED)
Liang Wu, Yujun Zhang

The topological Hall effect (THE) originates from the real-space Berry phase that an electron gains when its spin follows the spatially varying non-trivial magnetization textures, such as skyrmions. Such topologically protected magnetization textures can provide great potential for information storage and processing. Since directly imaging the skyrmions or detecting the magnetic diffraction of skyrmion lattice are significantly more challenging than conducting Hall measurements, THE has been widely used to attest the presence of skyrmions. However, the key feature of THE, namely the bump/dip in the Hall signal is not sufficient proof of THE. Here, we use empirical numerical modeling to demonstrate all possible THE-like signals that two anomalous Hall effect (AHE) signals with opposite signs can superpose. Besides the reproduction of many published results by the numerical model, we propose an exotic {\lq THE\rq} could, in principle, emerge with finely tuned two-channel AHE. The importance of the scrupulous re-examination of the THE observed in experiments cannot be exaggerated.


Defect bulk-boundary correspondence of topological skyrmion phases of matter. (arXiv:2206.02251v2 [cond-mat.mes-hall] UPDATED)
Shu-Wei Liu, Li-kun Shi, Ashley M. Cook

Unpaired Majorana zero-modes are central to topological quantum computation schemes as building blocks of topological qubits, and are therefore under intense experimental and theoretical investigation. Their generalizations to parafermions and Fibonacci anyons are also of great interest, in particular for universal quantum computation schemes. In this work, we find a different generalization of Majorana zero-modes in effectively non-interacting systems, which are zero-energy bound states that exhibit a cross structure -- two straight, perpendicular lines in the complex plane -- composed of the complex number entries of the zero-mode wavefunction on a lattice, rather than a single straight line formed by complex number entries of the wavefunction on a lattice as in the case of an unpaired Majorana zero-mode. These cross zero-modes are realized for topological skyrmion phases under certain open boundary conditions when their characteristic momentum-space spin textures trap topological defects. They therefore serve as a second type of bulk-boundary correspondence for the topological skyrmion phases. In the process of characterizing this defect bulk-boundary correspondence, we develop recipes for constructing physically-relevant model Hamiltonians for topological skyrmion phases, efficient methods for computing the skyrmion number, and introduce three-dimensional topological skyrmion phases into the literature.


Toward a correct theory of the fractional quantum Hall effect: What is the ground state of a quantum Hall system at $\nu=1/3$?. (arXiv:2206.05152v4 [cond-mat.mes-hall] UPDATED)
S. A. Mikhailov

The fractional quantum Hall effect was experimentally discovered in 1982. It was observed that the Hall conductivity $\sigma_{yx}$ of a two-dimensional electron system is quantized, $\sigma_{yx}=e^2/3h$, in the vicinity of the Landau level filling factor $\nu=1/3$. In 1983, Laughlin proposed a many-body variational wave function, which he claimed described a ``new state of matter'' -- a homogeneous incompressible liquid with fractionally charged quasi-particles. Here I develop an exact diagonalization theory that makes it possible to calculate the energy and other physical properties of the ground and excited states of a system of $N$ two-dimensional Coulomb interacting electrons in a strong magnetic field and in the field of a compensating positively charged background. The only assumption of the theory is that all electrons are assumed to be in the lowest Landau level. I present results for $N\le 7$ and show that the true ground state resembles a sliding Wigner crystal. I also calculate the physical properties of the $\nu=1/3$ Laughlin state for $N\le 8$ and show that properties of the ``Laughlin liquid'' are quantitatively and qualitatively different from those of the true ground state. In addition, I show that the variational principle that was used for the estimate of the Laughlin state energy in the thermodynamic limit does not work in this limit, since one can specify an infinitely large number of different trial wave functions giving the same variational energy at $N\to\infty$. I also show that some physical properties of the Laughlin liquid contradict fundamental physical principles.


Boundary and domain wall theories of 2d generalized quantum double model. (arXiv:2207.03970v5 [quant-ph] UPDATED)
Zhian Jia, Dagomir Kaszlikowski, Sheng Tan

The generalized quantum double lattice realization of 2d topological orders based on Hopf algebras is discussed in this work. Both left-module and right-module constructions are investigated. The ribbon operators and the classification of topological excitations based on the representations of the quantum double of Hopf algebras are discussed. To generalize the model to a 2d surface with boundaries and surface defects, we present a systematic construction of the boundary Hamiltonian and domain wall Hamiltonian. The algebraic data behind the gapped boundary and domain wall are comodule algebras and bicomodule algebras. The topological excitations in the boundary and domain wall are classified by bimodules over these algebras. The ribbon operator realization of boundary-bulk duality is also discussed. Finally, via the Hopf tensor network representation of the quantum many-body states, we solve the ground state of the model in the presence of the boundary and domain wall.


Unruh Effect and Takagi's Statistics Inversion in Strained Graphene. (arXiv:2209.08053v3 [cond-mat.mes-hall] UPDATED)
Anshuman Bhardwaj, Daniel E. Sheehy

We present a theoretical study of how a spatially-varying quasiparticle velocity in honeycomb lattices, achievable using strained graphene or in engineered cold-atom optical lattices that have a spatial dependence to the local tunneling amplitude, can yield the Rindler Hamiltonian embodying an observer accelerating in Minkowski spacetime. Within this setup, a sudden switch-on of the spatially-varying tunneling (or strain) yields a spontaneous production of electron-hole pairs, an analogue version of the Unruh effect characterized by the Unruh temperature. We discuss how this thermal behavior, along with Takagi's statistics inversion, can manifest themselves in photo-emission and scanning tunneling microscopy experiments. We also calculate the average electronic conductivity and find that it grows linearly with frequency $\omega$. Finally, we find that the total system energy at zero environment temperature looks like Planck's blackbody result for photons due to the aforementioned statistics inversion, whereas for an initial thermally excited state of fermions, the total internal energy undergoes stimulated particle reduction.


A fermion neural network with efficient optimization and quantum applicability. (arXiv:2211.05793v2 [quant-ph] UPDATED)
Pei-Lin Zheng, Jia-Bao Wang, Yi Zhang

Classical artificial neural networks have witnessed widespread successes in machine-learning applications. Here, we propose fermion neural networks (FNNs) whose physical properties, such as local density of states or conditional conductance, serve as outputs, once the inputs are incorporated as an initial layer. Comparable to back-propagation, we establish an efficient optimization, which entitles FNNs to competitive performance on challenging machine-learning benchmarks. FNNs also directly apply to quantum systems, including hard ones with interactions, and offer in-situ analysis without preprocessing or presumption. Following machine learning, FNNs precisely determine topological phases and emergent charge orders. Their quantum nature also brings various advantages: quantum correlation entitles more general network connectivity and insight into the vanishing gradient problem, quantum entanglement opens up novel avenues for interpretable machine learning, etc.


Vibrational phenomena in glasses at low temperatures captured by field theory of disordered harmonic oscillators. (arXiv:2211.10891v2 [cond-mat.dis-nn] UPDATED)
Florian Vogel, Matthias Fuchs

We investigate the vibrational properties of topologically disordered materials by analytically studying particles that harmonically oscillate around random positions. Exploiting classical field theory in the thermodynamic limit at $T=0$, we build up a self-consistent model by analyzing the Hessian utilizing Euclidean Random Matrix theory. In accordance with earlier findings [T. S. Grigera et al.J.~Stat.~Mech.~11 (2011) P02015.], we take non-planar diagrams into account to correctly address multiple local scattering events. By doing so, we end up with a first principles theory that can predict the main anomalies of athermal disordered materials, including the boson peak, sound softening, and Rayleigh damping of sound. In the vibrational density of states, the sound modes lead to Debye's law for small frequencies. Additionally, an excess appears in the density of states starting as $\omega^4$ in the low frequency limit, which is attributed to (quasi-) localized modes.


Stacking-Induced Symmetry-Protected Topological Phase Transitions. (arXiv:2302.07633v2 [cond-mat.mes-hall] UPDATED)
Sang-Jun Choi, Björn Trauzettel

We study symmetry-protected topological (SPT) phase transitions induced by stacking two gapped one-dimensional subsystems in BDI symmetry class. The topological invariant of the entire system is a sum of three topological invariants: two from each subsystem and an emerging topological invariant from the stacking. We find that any symmetry-preserving stacking of topologically trivial subsystems can drive the entire system into a topologically nontrivial phase. We explain this intriguing SPT phase transitions by conditions set by orbital degrees of freedom and time-reversal symmetry. To exemplify the SPT transition, we provide a concrete model which consists of an atomic chain and a spinful nanowire with spin-orbit interaction and $s$-wave superconducting order. The stacking-induced SPT transition drives this heterostructure into a zero-field topological superconducting phase.


Line Defect RG Flows in the $\varepsilon$ Expansion. (arXiv:2302.14069v3 [hep-th] UPDATED)
William H. Pannell, Andreas Stergiou

A general analysis of line defect renormalisation group (RG) flows in the $\varepsilon$ expansion below $d=4$ dimensions is undertaken. The defect beta function for general scalar-fermion bulk theories is computed to next-to-leading order in the bulk couplings. Scalar models as well as scalar-fermion models with various global symmetries in the bulk are considered at leading non-trivial order. Different types of potential infrared (IR) defect conformal field theories (dCFTs) and their RG stability are discussed. The possibility of multiple IR stable dCFTs is realised in specific examples with hypertetrahedral symmetry in the bulk. The one-point function coefficient of the order parameter in the stable IR dCFT of the cubic model is computed at next-to-leading order and compared with that in the IR dCFT of the Heisenberg model.


Tuning friction via topologically electro-convoluted lipid-membrane boundary layers. (arXiv:2303.08555v3 [cond-mat.soft] UPDATED)
Di Jin, Jacob Klein

It was recently discovered that friction between surfaces bearing phosphatidylcholine (PC) lipid bilayers can be increased by two orders of magnitude or more via an externally-applied electric field, and that this increase is fully reversible when the field is switched off. While this striking effect holds promising application potential, its molecular origin remains unknown due to difficulty in experimentally probing confined membrane structure at a molecular level. Our earlier molecular dynamics simulations revealed the equilibrium electroporated structure of such confined lipid membranes under an electric field; here we extend this approach to study the associated sliding friction between two solid surfaces across such PC bilayers. We identify the enhanced friction in the field as arising from membrane undulations due to the electroporation; this leads to some dehydration at the lipid-water interfaces, leading to closer contact and thus increased attraction between the zwitterionic headgroups, which results in increased frictional dissipation between the bilayers as they slide past each other. Additionally, the electric field facilitates formation of lipid bridges spanning the intersurface gap; at the sliding velocities of the experiments, these bridges increase the friction by topologically-forcing the slip-plane to pass through the acyl tail-tail interface, associated with higher dissipation during sliding. Our results account quantitatively for the experimentally-observed electro-modulated friction with boundary lipid bilayers, and indicate more generally how they may affect interactions between contacting surfaces, where high local transverse fields may be ubiquitous.


Tuning the electron-phonon interaction via exploring the interrelation between Urbach energy and Fano-type asymmetric Raman line shape in GO-hBN nanocomposites. (arXiv:2305.01362v3 [cond-mat.mtrl-sci] UPDATED)
Vidyotma Yadav, Tanuja mohanty

Hexagonal boron nitride (hBN), having an in-plane hexagonal structure in the sp2 arrangement of atoms, proclaims structural similarity with graphene with only a small lattice mismatch. Despite having nearly identical atomic arrangements and exhibiting almost identical properties, the electronic structures of the two materials are fundamentally different. Considering the aforementioned context, a new hybrid material with enhanced properties can be evolved combining both materials. This experiment involves liquid phase exfoliation of hBN and two-dimensional nanocomposites of GO-hBN with varying hBN and graphene oxide (GO) ratios. The optical and vibrational studies conducted using UV-Vis absorption and Raman spectroscopic analysis report the tuning of electron-phonon interaction (EPI) in the GO-hBN nanocomposite as a function of GO content (%). This interaction depends on disorder-induced electronic and vibrational modifications addressed by Urbach energy (Eu) and asymmetry parameter (q), respectively. The EPI contribution to the induced disorders estimated from UV-Vis absorption spectra is represented as EPI strength (Ee-p) and its impact observed in Raman phonon modes is quantified as an asymmetry parameter (q). The inverse of the asymmetry parameter is related to Ee-p, as Ee-p ~ 1/|q|. Here in this article, a linear relationship has been established between Eu and the proportional parameter (k), where k is determined as the ratio of the intensity of specific Raman mode (I) and q2, explaining the disorders' effect on Raman line shape. Thus a correlation between Urbach energy and the asymmetry parameter of Raman mode confirms the tuning of EPI with GO content (%) in GO-hBN nanocomposite.


Found 4 papers in prb
Date of feed: Fri, 09 Jun 2023 03:17:05 GMT

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Nonreciprocal transmission of magnetoacoustic waves in compensated synthetic antiferromagnets
M. Küß, M. Hassan, Y. Kunz, A. Hörner, M. Weiler, and M. Albrecht
Author(s): M. Küß, M. Hassan, Y. Kunz, A. Hörner, M. Weiler, and M. Albrecht

We investigate the interaction between surface acoustic waves (SAWs) and spin waves (SWs) in a Pt/Co($2\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$)/Ru($0.85\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$)/Co($2\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$)/Pt compensated synthetic antiferromagnet (SAF) composed of…


[Phys. Rev. B 107, 214412] Published Thu Jun 08, 2023

Scaling behavior of order parameters for the hybrid improper ferroelectric ${(\mathrm{Ca},\mathrm{Sr})}_{3}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$
Jing Kong, Alicia Manjón-Sanz, Jue Liu, Frederick Marlton, Tsz Wing Lo, Dangyuan Lei, Mads Ry Vogel Jørgensen, and Abhijit Pramanick
Author(s): Jing Kong, Alicia Manjón-Sanz, Jue Liu, Frederick Marlton, Tsz Wing Lo, Dangyuan Lei, Mads Ry Vogel Jørgensen, and Abhijit Pramanick

We show that in contrast to the conventional view of a mean-field Landau-type behavior, the oxygen octahedral tilt $(R)$ and polarization $(P)$ in the ${A}_{3}{B}_{2}{\mathrm{O}}_{7}$ Ruddlesden-Popper hybrid improper ferroelectric ${(\mathrm{Ca},\mathrm{Sr})}_{3}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$ e…


[Phys. Rev. B 107, 224103] Published Thu Jun 08, 2023

Fully gapped superconductivity and topological aspects of the noncentrosymmetric superconductor TaReSi
T. Shang, J. Z. Zhao, Lun-Hui Hu, D. J. Gawryluk, X. Y. Zhu, H. Zhang, J. Meng, Z. X. Zhen, B. C. Yu, Z. Zhou, Y. Xu, Q. F. Zhan, E. Pomjakushina, and T. Shiroka
Author(s): T. Shang, J. Z. Zhao, Lun-Hui Hu, D. J. Gawryluk, X. Y. Zhu, H. Zhang, J. Meng, Z. X. Zhen, B. C. Yu, Z. Zhou, Y. Xu, Q. F. Zhan, E. Pomjakushina, and T. Shiroka

We report a study of the noncentrosymmetric TaReSi superconductor by means of the muon-spin rotation and relaxation $(μ\mathrm{SR})$ technique, complemented by electronic band-structure calculations. Its superconductivity, with ${T}_{c}=5.5\phantom{\rule{0.28em}{0ex}}\text{K}$ and upper critical fie…


[Phys. Rev. B 107, 224504] Published Thu Jun 08, 2023

Spectral phase singularity and topological behavior in perfect absorption
Mengqi Liu, Weijin Chen, Guangwei Hu, Shanhui Fan, Demetrios N. Christodoulides, Changying Zhao, and Cheng-Wei Qiu
Author(s): Mengqi Liu, Weijin Chen, Guangwei Hu, Shanhui Fan, Demetrios N. Christodoulides, Changying Zhao, and Cheng-Wei Qiu

Perfect absorbers, which can achieve total absorption of all incoming energy, have been extensively studied in the last decades for various important technologies in general wave systems. Here, we show that perfect absorption (PA) is generically associated with topological spectral phase singularity…


[Phys. Rev. B 107, L241403] Published Thu Jun 08, 2023

Found 1 papers in nano-lett
Date of feed: Thu, 8 Jun 2023 15:13:55 GMT

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[ASAP] Twisted Bilayer Graphene Induced by Intercalation
Bixuan Li, Juntian Wei, Chunqiao Jin, Kunpeng Si, Lingjia Meng, Xingguo Wang, Yangyu Jia, Qianqian He, Peng Zhang, Jinliang Wang, and Yongji Gong

TOC Graphic

Nano Letters
DOI: 10.1021/acs.nanolett.3c00560

Found 1 papers in science-adv
Date of feed: Wed, 07 Jun 2023 19:03:57 GMT

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In-plane anisotropy of graphene by strong interlayer interactions with van der Waals epitaxially grown MoO3
Hangyel Kim, Jong Hun Kim, Jungcheol Kim, Jejune Park, Kwanghee Park, Ji-Hwan Baek, June-Chul Shin, Hyeongseok Lee, Jangyup Son, Sunmin Ryu, Young-Woo Son, Hyeonsik Cheong, Gwan-Hyoung Lee
Science Advances, Volume 9, Issue 23, June 2023.