The intermetallic germanide ${\mathrm{Gd}}_2{\mathrm{Pt}}_{1.1}{\mathrm{Ge}}_{2.9}$ was synthesized using an arc-melting method. The crystal structure was characterized using powder x-ray diffraction, revealing a disordered ternary ${\mathrm{AlB}}_2$-type structure (space group $P6/mmm$, No. 191) with lattice parameters $a=4.2092\left(1\right)\AA$ and $c=4.0546\left(2\right)\AA$. Physical properties were investigated by magnetic susceptibility and heat capacity measurements, which indicated onset of antiferromagnetic order at $T_t=8\mathrm{K}$. The obtained properties were compared with the ones reported for other members of the ${\mathrm{AlB}}_2$-type ${\mathrm{Gd}}_{2}T{\mathrm{Ge}}_3$ ($T=\mathrm{Ni}$, Cu, and Pd) family. The magnetic ordering in these compounds was discussed in terms of their crystal structure and the influence of Gd ions.

We study the $O\left(N\right)$-invariant ${\varphi }^4$ model on the simple cubic lattice by using Monte Carlo simulations. By using a finite-size scaling analysis, we obtain accurate estimates for the critical exponents $\nu$ and $\eta$ for $N=4$, 5, 6, 8, 10, and 12. We study the model for each $N$ for at least three different values of the parameter $\lambda$ to control leading corrections to scaling. We compare our results with those obtained by other theoretical methods.

Quantum criticality plays an important role in the unconventional nature of superconductivity in strongly correlated electron systems. However, the intrinsic antiferromagnetic (AFM) order parameter responsible for quantum criticality has been unidentified in the prototypical unconventional superconductor ${\mathrm{CeCoIn}}_5$. In this work, magnetization and specific-heat measurements for $\mathrm{CeCo}{\left({\mathrm{In}}_{1-x}{\mathrm{Zn}}_x\right)}_5$ with $x\le 0.07$ demonstrate that the field-induced AFM order develops with Zn doping, along with a continuous increase in its critical field up to 10 T at $x=0.07$. The weak signals associated with the AFM phase transition strongly suggest spatially inhomogeneous evolution of the AFM phase, whose feature becomes pronounced with decreasing the Zn concentration. The temperature, magnetic field, and Zn concentration phase diagram is constructed from those experimental results. It is found that, in this diagram, extrapolating the $x$ dependence of the AFM critical field yields the value of $\approx 5\mathrm{T}$ for $x\to 0$, which coincides with the location of the quantum critical point in ${\mathrm{CeCoIn}}_5$. The specific heat shows $-lnT$ diverging behavior characteristic of the non-Fermi-liquid state at the AFM critical fields for all of the $x$ range. The scaling analysis for the specific-heat data above critical fields leads to continuous variations of the scaling parameters as a function of $x$. These findings provide strong evidence that the quantum critical fluctuations in ${\mathrm{CeCoIn}}_5$ originate from the order parameter corresponding to the field-induced AFM state observed in Zn-doped systems.

Band topology is both constrained and enriched by the presence of symmetry. The importance of antiunitary symmetries such as time reversal was recognized early on leading to the classification of topological band structures based on the ten-fold way. Since then, lattice point group and nonsymmorphic symmetries have been seen to lead to a vast range of possible topologically nontrivial band structures many of which are realized in materials. In this paper, we show that band topology is further enriched in many physically realizable instances where magnetic and lattice degrees of freedom are wholly or partially decoupled. The appropriate symmetry groups to describe general magnetic systems are the spin-space groups. Here we describe cases where spin-space groups are essential to understand the band topology in magnetic materials. We then focus on magnon band topology where the theory of spin-space groups has its simplest realization. We consider magnetic Hamiltonians with various types of coupling including Heisenberg and Kitaev couplings revealing a hierarchy of enhanced magnetic symmetry groups depending on the nature of the lattice and the couplings. We describe, in detail, the associated representation theory and compatibility relations thus characterizing symmetry-enforced constraints on the magnon bands revealing a proliferation of nodal points, lines, planes, and volumes.

Hybrid systems that combine spin ensembles and superconducting circuits provide a promising platform for implementing quantum information processing. We propose a non-Hermitian magnon-circuit-QED hybrid model consisting of two cavities and an yttrium iron garnet (YIG) sphere placed in one of the cavities. Abundant exceptional points (EPs), parity-time ($\mathcal{PT}$)-symmetry phases, and $\mathcal{PT}$-symmetry broken phases are investigated in the parameter space. Tripartite high-dimensional entangled states can be generated steadily among modes of the magnon and photons in $\mathcal{PT}$-symmetry broken phases, corresponding to which the stable quantum coherence exists. Results show that the tripartite high-dimensional entangled state is robust against the dissipation of hybrid system, independent of a certain initial state, and insensitive to the fluctuation of magnon-photon coupling. Further, we propose to simulate the hybrid model with an equivalent $LCR$ circuit. This paper may provide prospects for realizing multipartite high-dimensional entangled states in the magnon-circuit-QED hybrid system.

We report temperature-dependent Raman scattering and x-ray diffraction studies of pyrochlore iridates ${\left({\mathrm{Eu}}_{1-x}{\mathrm{Bi}}_x\right)}_2{\mathrm{Ir}}_2{\mathrm{O}}_7$, for $x=0$, 0.02, 0.035, 0.05, and 0.1. The temperature variation in Raman experiments spans from 4 to 300 K, covering the metal-insulator phase transition accompanied by paramagnetic–to–all-in/all-out (AIAO) spin ordering ($T_{\mathrm{N}}$). These systems also show a Weyl semimetal (WSM) phase at low temperatures ($<\sim 50\mathrm{K}$). The Ir-O-Ir bond bending mode $A_{1g}$ (510 $\mathrm{c}{\mathrm{m}}^{\text{−}1}$) shows anomalous softening (for $x=0.0$, 0.02, 0.035, and 0.05) in the magnetically ordered AIAO state, arising primarily from the spin-phonon interaction due to the phonon modulation of the Dzyaloshinskii-Moriya spin-exchange interaction. The two stretching modes $T_{2g}^1$ (307 $\mathrm{c}{\mathrm{m}}^{\text{−}1}$) and $T_{2g}^2$ (382 $\mathrm{c}{\mathrm{m}}^{\text{−}1}$) harden significantly in the magnetic insulating phase. The $T_{2g}$ phonons (for $x=0.0$, 0.02, 0.035, and 0.05) also show anomalous temperature dependence of their mode frequencies above $T_{\mathrm{N}}$ due to strong electron-phonon coupling. The signatures of the WSM state are observed clearly in phonon renormalization $<50\mathrm{K}$ (in $x=0.02$) due to strong electron-phonon interaction. Our experimental results establish strong magneto-elastic coupling below $T_{\mathrm{N}}$ and significant electron-phonon interactions in the metallic phase above $T_{\mathrm{N}}$ as well as in the low-temperature WSM state.

Motivated by the ever-improving performance of deep learning techniques, we design a mixed input convolutional neural network approach to predict transport properties in deformed nanoscale materials using a height map of deformations, as can be obtained from scanning probe measurements, as input. We employ our approach to study electrical transport in a graphene nanoribbon deformed by a number of randomly positioned nanobubbles. Our network is able to make conductance predictions valid to an average error of 4.3%. We find that such low average errors are achieved by a redundant input of energy values, yielding predictions that are 30%–40% more accurate than conventional architectures. We demonstrate that the same method can learn to predict the valley-resolved conductance, with success specifically in identifying the energy at which intervalley scattering becomes prominent. We demonstrate the robustness of the approach by testing the pretrained network on samples with deformations differing in number and shape from the training data. We furthermore employ a graph theoretical analysis of the structure and outputs of the network and conclude that a tight-binding Hamiltonian can be effectively encoded in the first layer of the network, which is supported by numerical findings. Our approach contributes a theoretical understanding and a refined methodology to the application of deep learning for the determination of transport properties based on real-space disorder information.

In a slab geometry with large surface-to-bulk ratio, topological surface states such as Fermi arcs for Weyl or Dirac semimetals may dominate their low-energy properties. We investigate the collective charge oscillations in such systems, finding striking differences between Weyl and conventional electronic systems. Our results, obtained analytically and verified numerically, predict that time-reversal symmetry-broken Weyl semimetal thin films will host a single $\omega \propto \sqrt{q}$ plasmon mode that results from collective, antisymmetric charge oscillations between the two surfaces, in stark contrast to conventional 2D bilayers as well as Dirac semimetals with Fermi arcs, which support antisymmetric acoustic modes along with a symmetric optical mode. These modes lie in the gap of the particle-hole continuum and are thus spectroscopically observable and potentially useful in plasmonic applications.

The quantum Hall system can be used to study many-body physics owing to its multiple internal electronic degrees of freedom and tunability. While quantum phase transitions have been studied intensively, research on the temperature-induced phase transitions of this system is limited. We measured the pure bulk conductivity of a quantum Hall antiferromagnetic state in bilayer graphene over a wide range of temperatures and revealed the two-step phase transition associated with the breaking of the long-range order, i.e., the Kosterlitz-Thouless transition, and short-range antiferromagnetic order. Our findings are fundamental to understanding electron correlation in quantum Hall systems.

In Yang et al. [Nature 576, 248 (2019)], the authors introduced a general theoretical framework for nanoscale electromagnetism based on Feibelman parameters. Here quantum effects of the optically excited electrons at the interface between two materials are lumped into two complex-valued and frequency-dependent parameters which can be incorporated into modified boundary conditions for Maxwell's equations, the so-called mesoscopic boundary conditions. These modifications can, in principle, be implemented in any Maxwell solver, although the technicalities can be subtle and depend on the chosen computational approach. In this paper, we show how to implement mesoscopic boundary conditions in a boundary element method approach based on a Galerkin scheme with Raviart-Thomas shape elements for the representation of the tangential electromagnetic fields at the boundary. We demonstrate that the results of our simulations are in perfect agreement with Mie theory, including Feibelman parameters, and that for typical simulation scenarios the computational overhead is usually small.

We use a classical dielectric response framework to evaluate the force components acting on a point charge that moves parallel to an anisotropic two-dimensional material representing doped phosphorene. The anisotropic response of phosphorene is captured by a simple analytical conductivity model that combines contributions from its inter- and intraband electronic transitions, thereby giving rise to a topological transition between elliptic and hyperbolic isofrequency curves for its plasmon modes in the terahertz to the midinfrared frequency range. Pairing this model with a simple dielectric description of a ${\mathrm{SiO}}_2$ substrate further reveals the effects of plasmon hybridization with optical phonons in the substrate. We have found that the force on the incident charge has three components, which all exhibit strong velocity-dependent anisotropy when its direction of motion is varied with respect to the principal directions of the phosphorene's conductivity tensor. Besides the longitudinal stopping force and the dynamic image force, there arises a transverse stopping force, with a magnitude comparable to that of the longitudinal force, which acts parallel to the target surface and perpendicular to the trajectory of the particle, and can be therefore experimentally observable, even after its magnitude is reduced by the presence of the substrate. In addition, we have found that the dynamic image force can become repulsive when the particle moves along the armchair direction of a freestanding phosphorene, but the presence of the substrate eliminates that surprising but implausible consequence of the adopted model for anisotropic conductivity of that material.

Spin-orbit coupling (SOC), which can induce spin flip during the relaxation of photoexcited charge carrier, plays a crucial role in spin dynamics. In this work, we have used time-domain ab initio nonadiabatic molecular dynamics (NAMD) method to study the SOC induced ultrafast demagnetization in Ni at $300\mathrm{K}$. The spin-diabatic representation using spin-polarized Kohn-Sham (KS) basis sets and spin-adiabatic representation using spinor basis sets have been applied, and both of them achieve demagnetization in Ni with a timescale around $100\mathrm{fs}$. The spin-diabatic representation suggests a picture that the electron-phonon coupling (EPC) provides direct energy relaxation channel among the same-spin states, while the SOC can induce spin flip. After photoexcitation, it is found the spin-minority electrons relax to the same-spin states rather than the opposite-spin states, since EPC is larger than SOC by one order of magnitude. By contrast, for the spin-majority electrons, spin flip occurs since there are no empty same-spin states as electron acceptor above the Fermi level. The different relaxation pathways for spin-majority and spin-minority electrons induce the demagnetization. The spin-adiabatic representation provides an Elliott-Yafet spin-phonon scattering picture. The SOC induced reduction of magnetic moment in Ni may induce magnon to drive further demagnetization. The ab initio NAMD simulation provides a critical angle to understand how the SOC and EPC affect demagnetization process in Ni.

The metal-insulator transition (MIT) phenomenon in materials is associated with a complex interplay of electronic correlations, magnetism, and strain effects. We image the current distribution around MIT in ${\mathrm{NdNiO}}_3$ thin film with a thickness gradient. Above the MIT temperature, we observe a homogeneous current distribution implying the film is uniformly metallic. Below the MIT temperature, an insulating phase forms and spreads from the thicker to thinner regions of the film, leading to a nonuniform current distribution. A thickness variation induced strain distribution causes a spread in the local MIT temperature across the film. Our analysis shows the bulk resistance represents changes in the area of the metallic phase across the MIT. Our study suggests that the MIT in the nickelate film is a first-order transition from a paramagnetic non-Fermi-liquid metallic to an antiferromagnetic insulating phase. Strain distribution across the film broadens the transition.

In this paper we examine the possibility of Floquet engineering in the three candidate Kitaev materials ${\mathrm{Na}}_2{\mathrm{IrO}}_3$, $\alpha \text{−}{\mathrm{Li}}_2{\mathrm{IrO}}_3$, and $\alpha \text{−}{\mathrm{RuCl}}_3$. We derive an effective Floquet Hamiltonian and give an approximation for heating processes arising from doublon holon propagation. This suggests that compounds with stronger Hund's rule coupling are less prone to heating. We then investigate the impact of light frequency and amplitude on magnetic interaction terms up to third nearest neighbor and find that third neighbor Heisenberg coupling $J_3$ is very susceptible to tuning by circularly polarized light. Finally, we discuss uses of linear polarized light in selectively tuning single bond directions.

We study thermal correlation functions of the one-dimensional impenetrable lattice anyons. These correlation functions can be presented as a difference of two Fredholm determinants. To describe the large-time and long-distance behavior of these objects, we use the effective form-factor approach. The asymptotic behavior is different in the spacelike and timelike regions. In particular, in the timelike region we observe the additional power factor on top of the exponential decay. We argue that this result is universal as it is related to the discontinuous behavior of the phase shift function of the effective fermions. At particular values of the anyonic parameter, we recover the asymptotics of the spin-spin correlation functions in the $XX$ quantum chain.

We present a theoretical study of the electronic, spectral, and magnetic properties of ternary $RE\mathrm{ScSi}$ and $RE\mathrm{ScGe}$ $(RE=\mathrm{La},\mathrm{Ce})$ compounds based on the $\mathrm{DFT}+\mathrm{DMFT}$ method combining Density Functional Theory with Dynamical Mean-Field Theory. In this work, we find that Ce-based compounds, similar to LaScSi, exhibit electride-like features. Our calculations reveal that not only silicide $RE\mathrm{ScSi}$ compounds, but also their germanide $RE\mathrm{ScGe}$ analogs, exhibit high interstitial density characteristic of electrides. Remarkably, we find that both rare-earth $5d$ and scandium $3d$ contribute electrons to the strongly localized interstitial electron density, which can be considered as an electride anion with pronounced $s$ symmetry. In addition, we show that the Ce-based compounds show effects of strong electronic correlations in the $4f$ shell of cerium ions and strongly resemble those of $\gamma \text{−}\mathrm{Ce}$.

Supersymmetry (SUSY), originally proposed in particle physics, refers to a dual relation that connects fermionic and bosonic degrees of freedom in a system. Recently, there has been considerable interest in applying the idea of SUSY to topological phases, motivated by the attempt to gain insights from the fermion side into the boson side and vice versa. We present a systematic study of this construction when applied to band topology in noninteracting systems. First, on top of the conventional tenfold way, we find that topological insulators and superconductors are divided into three classes depending on whether the supercharge can be local and symmetric, must break a symmetry to preserve locality, or needs to break locality. Second, we resolve the apparent paradox between the nontriviality of free fermions and the triviality of free bosons by noting that the topological information is encoded in the identification map. We also discuss how to understand a recently revealed SUSY entanglement duality in this context. These findings are illustrated by prototypical examples. In this paper, we shed light on band topology from the perspective of SUSY.

We propose a non-Hermitian topological system protected by the generalized rotational symmetry which invokes rotation in space and Hermitian conjugation. The system, described by the tight-binding model with reciprocal imaginary next-nearest-neighbor hopping, is found to host two pairs of in-gap edge modes in the gapped topological phase, and is characterized by the non-Hermitian (NH) Chern number $C_{\mathrm{NH}}=2$. The quantization of the NH Chern number is shown to be protected by the generalized rotational symmetry ${\widehat{H}}^{+}\left(\mathrm{g}\vec{k}\right)={\widehat{U}}_g\widehat{H}\left(\vec{k}\right){\widehat{U}}_g^{+}$ of the system. Our finding paves the way towards non-Hermitian topological systems characterized by large values of topological invariants and hosting multiple in-gap edge states, which can be used for topologically resilient multiplexing.

Using density functional theory, a competition between the Mott-Hubbard and intervalence charge transfer mechanism of electron localization is revealed in ${\mathrm{AgF}}_2$, an important silver analog of oxocuprates. We show that at reduced temperature and electron correlations ${\mathrm{AgF}}_2$ becomes metallic and dynamically unstable with respect to soft phonon modes that promote charge ordering. The charge density wave (CDW) instability is closely related to the Kohn anomaly and Fermi surface nesting. The long advocated ${\mathrm{KBrF}}_4$-type CDW ${\mathrm{Ag}}^{1+/3+}{\mathrm{F}}_2$ structure and its facile transformation to the ground state ${\mathrm{Ag}}^{2+}{\mathrm{F}}_2$ phase is explained. Our results point to an intimate interplay between lattice, charge, and spin degrees of freedom in this seemingly simplistic binary metal fluoride.