Chiral edge states in a quantum Hall effect are the paradigmatic example of a quasiparticle with chirality. In even space-time dimensions, the Nielsen-Ninomiya theorem strictly forbids chiral states in physical isolation. The exceptions to this theorem only occur in the presence of nonlocality, non-Hermiticity, or by embedding the system at the boundary of the higher-dimensional bulk. In this Letter, using the IBM quantum computer platform, we realize a Floquet chiral quantum walk enabled by nonlocality. The unitary time-evolution operator is described by an effective Floquet Hamiltonian with long-ranged coupling. We find that the chiral wave packets lack the common features of conventional wave phenomena such as localization. The absence of localization is witnessed by the robustness against external perturbations. However, the intrinsic quantum errors of the current quantum device give rise to a finite lifetime where the chiral wave packet eventually disperses in the long-time limit. Nevertheless, we observe the stability of the chiral wave by comparing it with a conventional nonchiral model.

We find the fine structure splitting (FSS) of a single exciton, which splits its degenerate ground-state manifold into singlets, nearly vanishes in highly asymmetric quantum dots (QDs) due to the cancellation of splitting effects with markedly different origin. The dots simulated are those that emerge on top of etch pits through the droplet epitaxy growth process; these etch pit dots break square ($C_{4v}$) spatial symmetry, which has been previously associated with small FSS. Configuration interaction calculations predict a vanishing FSS at a specific finite etch pit displacement from the center of the dot, for a structure far from square symmetry. We thus predict that highly asymmetric QDs may still display negligible FSS, providing avenues for high-fidelity generation of indistinguishable, polarization entangled photon pairs on demand.

Charge density waves (CDWs) in two-dimensional (2D) materials have been a major focus of research in condensed matter physics for several decades due to their potential for quantum-based technologies. In particular, CDWs can induce a metal-insulator transition by coupling two Dirac fermions, resulting in the emergence of a topological phase. Following this idea, here we explore the behavior of three different CDWs in a 2D layered material, SnP, using both density functional theory calculations and experimental synthesis to study its stability. The layered structure of its bulk counterpart, ${\mathrm{Sn}}_4{\mathrm{P}}_3$, suggests that the structure can be synthesized down to the monolayer by chemical means. However, despite the stability of the bulk, the monolayer shows unstable phonons at $\mathrm{\Gamma }$, $K$, and $M$ points of the Brillouin zone, which lead to three possible CDW phases. All three CDWs lead to metastable insulating phases, with the one driven by the active phonon in the $K$ point being topologically nontrivial under strain. Strikingly, the ground-state structure is only revealed due to the presence of strong anharmonic effects. This underscores the importance of studying CDWs beyond the conventional harmonic picture, where the system's ground state can be elucidated solely from the harmonic phonon spectra.

Magic, or nonstabilizerness, characterizes how far away a state is from the stabilizer states, making it an important resource in quantum computing, under the formalism of the Gotteman-Knill theorem. In this paper, we study the magic of the one-dimensional (1D) random matrix product states (RMPSs) using the $L_1$-norm measure. We first relate the $L_1$ norm to the $L_4$ norm. We then employ a unitary four-design to map the $L_4$ norm to a 24-component statistical physics model. By evaluating partition functions of the model, we obtain a lower bound on the expectation values of the $L_1$ norm. This bound grows exponentially with respect to the qudit number $n$, indicating that the $1\mathrm{D}$ RMPS is highly magical. Our numerical results confirm that the magic grows exponentially in the qubit case.

The microscopic origin of the topological magnon band gap in ${\mathrm{CrI}}_3$ ferromagnets has been a subject of controversy for years since two main models with distinct characteristics, i.e., Dzyaloshinskii-Moriya (DM) and Kitaev, provided possible explanations with different outcome implications. Here, we investigate the angular magnetic field dependence of the magnon gap of ${\mathrm{CrI}}_3$ by elucidating what main contributions play a major role in its generation. We implement stochastic atomistic spin-dynamics simulations to compare the impact of these two spin interactions on the magnon spectra. We observe three distinct magnetic field dependencies between these two gap opening mechanisms. First, we demonstrate that the Kitaev-induced magnon gap is influenced by both the direction and amplitude of the applied magnetic field, while the DM-induced gap is solely affected by the magnetic field direction. Second, the position of the Dirac cones within the Kitaev-induced magnon gap shifts in response to changes in the magnetic field direction, whereas they remain unaffected by the magnetic field direction in the DM-induced gap scenario. Third, we find a direct-indirect magnon band gap transition in the Kitaev model by varying the applied magnetic field direction. These differences may distinguish the origin of topological magnon gaps in ${\mathrm{CrI}}_3$ and other van der Waals magnetic layers. Our findings pave the way for exploration and engineering topological gaps in van der Waals materials.

Realizing ideal Weyl semimetal state with a single pair of Weyl points has been a long-sought goal in the field of topological semimetals. Here, we reveal such a state in the Cr-based half-Heusler compounds $X\mathrm{CrTe}$ ($X=\mathrm{K}$, Rb). We show that these materials have a half-metal ground state, with the Fermi level crossing only one spin channel. Importantly, the Fermi surface is clean, consisting of the minimal number (i.e., a single pair) of spin-polarized Weyl points, so the state represents an ideal Weyl half-semimetal. We show that the locations of the two Weyl points and the associated Chern vector can be flexibly tuned by rotating the magnetization vector. The minimal surface Fermi arc pattern and its contribution to anomalous Hall transport are discussed. Our finding offers an ideal material platform for exploring magnetic Weyl fermions, which will also facilitate the interplay between Weyl physics and spintronics.

Dopant impurity potentials determined by ab initio supercell density functional theory calculations are used to calculate the optical conductivity of overdoped ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$ (LSCO) and ${\mathrm{Tl}}_2{\mathrm{Ba}}_2{\mathrm{CuO}}_{6+\delta }$ (Tl-2201) in the superconducting and normal states. Vertex corrections are included to account for the effect of forward scattering on two-particle properties. This approach was previously shown to provide good, semiquantitative agreement with measurements of superfluid density in LSCO. Here we compare calculations of conductivity with measurements of terahertz conductivity on LSCO using identical impurity, band, and correlation parameters and find similarly good correspondence with experiment. In the process, we delineate the impact of the different disorder mechanisms on single-particle and transport relaxation processes. In particular, we reveal the critical role of apical oxygen vacancies in transport scattering and show that transport relaxation rates in LSCO are significantly reduced when apical oxygen vacancies are annealed out. These considerations are shown to be crucial for understanding the variability of experimental results for overdoped LSCO in samples of nominally identical doping but different types. Finally, we give predictions for Tl-2201 terahertz conductivity experiments.

Atomistic simulations play an important role in elucidating the physical properties of iron at extreme pressure and temperature conditions, which in turn provide crucial insights into the present state and thermal evolution of the earth's and planetary cores. However, simulations face challenges in retaining ab initio accuracy at the simulation size and time scales required to address some of the most important geophysical questions. We used deep-learning methods to develop interatomic models for iron covering pressures from 75–650 GPa and temperatures from 4000–7600 K. The models retain ab initio accuracy while being computationally cost effective. Rigorous validation tests attest their accuracy in large-scale simulations as well as in the presence of extended defects. The models pave the way to the determination of the thermodynamic and rheological properties of iron at extreme conditions with ab initio accuracy.

In this paper, we present a method for generating a synthetic gauge field in the vertical direction by linearly modulating the mass term in a Dirac equation model. This allows for the quantization of Landau levels through the generated pseudomagnetic field, with the chiral zeroth Landau level being topologically protected. An elastic snake state is realized using the coupling between the zeroth and the first Landau levels. For demonstration, our theoretical predictions are realized numerically in an elastic medium of truss structures arranged in a honeycomb lattice. Our results, supported by theory and simulations, establish a framework for generating pseudomagnetic fields in elastic systems with potential applications in waveguides and cloaking.

Nonlinear systems possess complex dynamic behaviors and transition characteristics among various states, which make the behaviors of nonlinear systems hard to predict and control. Here we study state transfer in a nonlinear cavity magnonic system containing the photon and magnon Kerr effects. In this system, the magnon frequency shift exhibits bistability and tristability with coexisting stable states. A given initial state is transferred to one of the coexisting states. Although state transfer is shown from the perspective of the number of excited magnons, which is proportional to the magnon frequency shift, the coexisting state to which the initial state is transferred is determined jointly by the amplitude and phase of the magnon and photon, rather than by the number of excited magnons. Based on the basins of attraction, we explain state transfer and reveal its nonlinear feature. Our findings provide a deeper comprehension of complex dynamic behaviors and contribute to the exploration of effective methods and strategies for controlling different states in a nonlinear cavity magnonic system.

In a Josephson junction, the transfer of Cooper pairs from one superconductor to the other one can be associated with the formation of Andreev bound states. In a Josephson junction made with a semiconducting nanowire, the spin degeneracy of these Andreev states can be broken thanks to the presence of spin-orbit coupling and a finite phase difference between the two superconducting electrodes. The lifting of the spin degeneracy opened the way to the realization of Andreev spin qubits that do not require the application of a large magnetic field. So far the operation of these qubits relied on a Raman process involving two microwave tones and a third Andreev state [M. Hays et al., Science 373, 430 (2021)]. Still, time-reversal preserving impurities in the nanowire allow for spin-flip scattering processes. Here, using the formalism of scattering matrices, we show that these processes generically couple Andreev states with opposite spins. In particular, the nonvanishing current matrix element between them allows for the direct manipulation of phase-driven Andreev spin qubits, thereby circumventing the use of the above-mentioned Raman process.

Topological and valleytronic materials are promising for spintronic and quantum applications due to their unique properties. Using first principles calculations, we demonstrate that germanene (Ge)-based ferromagnetic heterostructures can exhibit multiple quantum states such as quantum anomalous Hall effect (QAHE) with Chern numbers of $C=-1$ or $C=-2$, quantum valley Hall effect (QVHE) with a valley Chern number of $C_v=2$, valley-polarized quantum anomalous Hall effect (VP-QAHE) with two Chern numbers of $C=-1$ and $C_v=-1,$ as well as time-reversal symmetry broken quantum spin Hall effect (T-broken QSHE) with a spin Chern number of $C_s\sim 1$. Furthermore, we find that the transitions between different quantum states can occur by changing the magnetic orientation of ferromagnetic layers through applying a magnetic field. Our discovery provides different routes and material platforms with a unique combination of diverse properties that make it well suitable for applications in electronics, spintronics, and valley electronics.

We present a hybrid numerical approach to simulate quantum many-body problems on two spatial dimensional quantum lattice models via the non-Abelian ab initio version of the density matrix renormalization group method on state-of-the-art high-performance computing infrastructures. We demonstrate that for the two-dimensional spinless fermion model and for the Hubbard model on torus geometry, altogether several orders of magnitude in computational time can be saved by performing calculations on an optimized basis and by utilizing hybrid CPU-multiGPU parallelization. At least an order of magnitude reduction in computational complexity results from mode optimization, while a further order of reduction in wall time is achieved by massive parallelization. Our results are measured directly in the number of floating point operations and seconds. A detailed scaling analysis of the obtained performance as a function of matrix ranks and as a function of system size up to $12\times 12$ lattice topology is discussed. Our CPU-multiGPU model also tremendously accelerates the calculation of the one- and two-particle reduced density matrices, which can be used to construct various order parameters and trace quantum phase transitions with high fidelity.

Recently, structural disorder-induced topological phase transitions in periodic systems have attracted much attention. However, in aperiodic systems such as quasicrystalline systems, the interplay between structural disorder and band topology is still unclear. In this work, we investigate the effects of structural disorder on a quantum spin Hall insulator phase and a higher-order topological phase in a two-dimensional Amman-Beenker tiling quasicrystalline lattice. We demonstrate that the structural disorder can induce a topological phase transition from a quasicrystalline normal insulator phase to an amorphous quantum spin Hall insulator phase, which is confirmed by bulk gap closing and reopening, robust edge states, a quantized spin Bott index, and conductance. Furthermore, the structural disorder-induced higher-order topological phase transition from a quasicrystalline normal insulator phase to an amorphous higher-order topological phase characterized by a quantized quadrupole moment and topological corner states is also found. More strikingly, the disorder-induced higher-order topological insulator with eight corner states represents a distinctive topological state that eludes realization in conventional crystalline systems. Our work extends the study of the interplay between disorder effects and topologies to quasicrystalline and amorphous systems.

We have investigated the magnetism and pairing correlations of the triangular lattice based on the Hubbard model using the determinant quantum Monte Carlo method and the constrained path Monte Carlo. The results show that the presence of the next-nearest-neighbor hopping integral $t^{\prime }$ introduces an additional energy scale to the system, and through $t^{\prime }$, one can regulate the shape of the density of states and thus the position of the van Hove singularity point. Increasing inverse temperature $\beta$ and on-site interaction $U$ favor the formation of ferromagnetic correlation in a rather large filling region, and the calculations for different lattice sizes show that the range of the ferromagnetic correlations is smaller than the smallest lattice simulated at the investigated temperatures. We study the different pairing correlations of the triangular lattice near several typical fillings and show that the $f$-wave pairing dominates the system in the filling region near the van Hove singularity point with a high density of states, where the ferromagnetic correlation is also enhanced. When the filling is close to half-filling, the pairing susceptibility with $f$ wave is suppressed and the pairing susceptibility of $f_n$ wave is enhanced, however, both the effective pairing interaction with $f$ wave and $f_n$ wave are negative, which indicates that neither $f$-wave nor $f_n$-wave superconductivity may exist. Finally, we find that the pairing channel of different symmetry in the system maybe closely related to the magnetic properties. Ferromagnetic fluctuation favors the formation of $f$-wave pairing, while antiferromagnetic fluctuation tends to promote $f_n$-wave pairing.

Exciton transport is a fundamental process that underlies the functionality of semiconductor optoelectronic devices. However, when excitons interact with one another, their transport pattern becomes unpredictable, posing a great challenge to harness their full potential in various applications. In our study, focusing on the exciton density change in a tungsten-disulfide monolayer, we observed that strong interactions between excitons can actually stop their movement. This finding contradicts the typical understanding of consistent exciton movement and reveals that a higher density might decrease the exciton-exciton annihilation rate due to reduced mobility. Our findings offer a valuable technique to examine exciton transport and deepen our grasp of their behavior in many-body interactions, which could pave the way for better-performing excitonic devices.

Collective plasmon excitations in solids that result from the process of photoemission are an important area of fundamental research. In this study, we identify a significant number ($n$) of multiple bulk plasmons ($n{\omega }_p$) in the hard x-ray photoelectron spectra of the core levels and valence bands (VBs) of two well-known, nearly free electron metals, aluminum (Al) and magnesium (Mg). On the basis of earlier theoretical works, we estimate the contributions of extrinsic, intrinsic, and interference processes to the intensities of $1s$ to $2s$ core-level plasmons. The intrinsic contribution diminishes from 21.7% for $1{\omega }_p$ to 4.4% for $2{\omega }_p$, and becomes negligible thereafter (0.5% for $3{\omega }_p$). The extrinsic and intrinsic plasmon contributions do not vary significantly across a broad range of photoelectron kinetic energies, and also between the two metals (Al and Mg). The interference contribution varies from negative to zero as $n$ increases. An asymmetric line shape is observed for the bulk plasmons, which is most pronounced for $1{\omega }_p$. Signature of the surface plasmon is detected in normal emission, and it exhibits a significantly increased intensity in the grazing emission. The VB spectra of Al and Mg, which are dominated by $s$-like states, exhibit excellent agreement with the calculated VB based on density functional theory. The VB exhibits four multiple bulk plasmon peaks in the loss region, which are influenced by an intrinsic process in addition to the extrinsic process. On a completely oxidized aluminum surface, the relative intensity of the Al metal bulk plasmon remains nearly unaltered, while the surface plasmon is completely attenuated.

The quest for realizing highly spin-polarized conduction in materials at room temperature is one of the central themes of materials physics. We report on the realization of a conducting interface in $\mathrm{LaFe}{\mathrm{O}}_3$ (LFO)-$\mathrm{SrTi}{\mathrm{O}}_3$ (STO) that demonstrates spin-polarization signatures, namely, negative magnetoresistance (MR) and anomalous Hall resistivity $>150$ K and even up to room temperature. However, the same system shows positive MR and normal Hall effect at temperatures $<150$ K. From density functional theory calculations, we find that this is related to the structural transition of the substrate, amplified here as the changes happen at the interface. This leads to a net spin polarization of the interface states at the Fermi energy in the high-temperature phase, allowing for an anomalous Hall effect and negative MR. In addition, this interface appears to be almost transparent in the entire range of visible light. Our observation might be viewed as a step toward room-temperature transparent oxide spintronics.

Topological quantum optics has endowed integrated quantum devices with novel functionalities, including unidirectional transport and immunity to structural defects. Here we propose topological interfaces that support two distinct edge modes with different frequency ranges. The nonlinear four-wave mixing processes in the topological interfaces lead to the generation of signal and idler photons, each corresponding to distinct edge modes. By designing a diamondlike topological structure, we can couple the signal and idler photons into opposite branches, leading to spatial separation of the photon pairs. This behavior enables on-chip generation and flexible control of the topological biphoton states. More importantly, the biphoton states are inborn topologically protected, showing robustness against sharp bends and disorders. Our proposal offers the possibility of robust, multifunctional topological quantum devices, which may find applications in quantum information processing.

The local atomic structure has long been recognized as a predominant characteristic and key to understanding glassy structures and properties. However, the factors governing the formation and evolution of these structures in metallic glasses remain elusive. Herein, we report an unexpected local structural crossover under pressure in a simple binary ${\mathrm{Zr}}_{65}{\mathrm{Ni}}_{35}$ metallic glass consisting of pure transition metals, evidenced by in situ high-pressure synchrotron x-ray diffraction and electrical resistivity measurements combined with ab initio molecular dynamics simulations. While the specific volume of the metallic glass (MG) follows a single-phase compression behavior without an apparent volume collapse, detailed analysis of the structural properties using structure factor, reduced pair-distribution function, and simulations reveals sharp changes of the Ni-centered clusters at ∼20 GPa in terms of their coordination numbers, atomic pair distances, and Voronoi polyhedra. This structural crossover is found to be closely linked to the enhanced contribution of the Ni $d$ orbital to the electron density of state at the Fermi level under high pressures. These results underscore the correlation between the local atomic structure and the intricate electronic structure, particularly the $3d$ electronic structure, in transition-metal MGs, which sheds light on the stability characteristics of local structures in MGs from an electronic structure point of view.