We develop a generic strategy and simple numerical models for multicomponent metallic glasses for which the swap Monte Carlo algorithm can produce highly stable equilibrium configurations equivalent to experimental systems cooled more than ${10}^7$ times slower than in conventional simulations. This paves the way for a deeper understanding of the thermodynamic, dynamic, and mechanical properties of metallic glasses. As first applications, we considerably extend configurational entropy measurements down to the experimental glass temperature, and demonstrate a qualitative change of the mechanical response of metallic glasses of increasing stability toward brittleness.

Materials with high thermal conductivities ($\kappa$) are valuable to solve the challenge of waste heat dissipation in highly integrated and miniaturized modern devices. Herein, we report the first synthesis of atomically thin isotopically pure hexagonal boron nitride (BN) and its one of the highest $\kappa$ among all semiconductors and electric insulators. Single atomic layer ($1L$) BN enriched with ${}^{11}\mathrm{B}$ has a $\kappa$ up to $1009\mathrm{W/}\mathrm{mK}$ at room temperature. We find that the isotope engineering mainly suppresses the out-of-plane optical (ZO) phonon scatterings in BN, which subsequently reduces acoustic-optical scatterings between ZO and transverse acoustic (TA) and longitudinal acoustic phonons. On the other hand, reducing the thickness to a single atomic layer diminishes the interlayer interactions and hence umklapp scatterings of the out-of-plane acoustic (ZA) phonons, though this thickness-induced $\kappa$ enhancement is not as dramatic as that in naturally occurring BN. With many of its unique properties, atomically thin monoisotopic BN is promising on heat management in van der Waals devices and future flexible electronics. The isotope engineering of atomically thin BN may also open up other appealing applications and opportunities in 2D materials yet to be explored.

Compression of liquid water up to multi-kbar pressures is known to perturb dramatically its local structure required for charge defects to migrate as topological defects in the hydrogen-bonded network. Our ab initio simulations show that the migration of excess protons is not much affected at 10 kbar, whereas that of proton holes is significantly reduced. Non-Markovian analyses show that this is not due to modifying the free energy barriers of both charge transfer and migration. It is rather pressure-induced modifications of the population of activated states, depending on interstitial water, which rules charge migration at extreme compression.

We perform momentum-conserving tunneling spectroscopy using a GaAs cleaved-edge overgrowth quantum wire to investigate adjacent quantum Hall edge states. We use the lowest five wire modes with their distinct wave functions to probe each edge state and apply magnetic fields to modify the wave functions and their overlap. This reveals an intricate and rich tunneling conductance fan structure which is succinctly different for each of the wire modes. We self-consistently solve the Poisson-Schrödinger equations to simulate the spectroscopy, reproducing the striking fans in great detail, thus, confirming the calculations. Further, the model predicts hybridization between wire states and Landau levels, which is also confirmed experimentally. This establishes momentum-conserving tunneling spectroscopy as a powerful technique to probe edge state wave functions.

We construct a dynamical decoupling protocol for accurately generating local and global symmetries in general many-body systems. Multiple commuting and noncommuting symmetries can be created by means of a self-similar-in-time (“polyfractal”) drive. The result is an effective Floquet Hamiltonian that remains local and avoids heating over exponentially long times. This approach can be used to realize a wide variety of quantum models, and nonequilibrium quantum phases.

Noether’s theorem relates constants of motion to the symmetries of the system. Here we investigate a manifestation of Noether’s theorem in non-Hermitian systems, where the inner product is defined differently from quantum mechanics. In this framework, a generalized symmetry that we term pseudochirality emerges naturally as the counterpart of symmetries defined by a commutation relation in quantum mechanics. Using this observation, we reveal previously unidentified constants of motion in non-Hermitian systems with parity-time and chiral symmetries. We further elaborate the disparate implications of pseudochirality induced constant of motion: It signals the pair excitation of a generalized “particle” and the corresponding “hole” but vanishes universally when the pseudochiral operator is antisymmetric. This disparity, when manifested in a non-Hermitian topological lattice with the Landau gauge, depends on whether the lattice size is even or odd. We further discuss previously unidentified symmetries of this non-Hermitian topological system, and we reveal how its constant of motion due to pseudochirality can be used as an indicator of whether a pure chiral edge state is excited.

Computational models are formulated in hierarchies of variable fidelity, often with no quantitative rule for defining the fidelity boundaries. We have constructed a dataset from a wide range of atomistic computational models to reveal the accuracy boundary between higher-fidelity models and a simple, lower-fidelity model. The symbolic decision boundary is discovered by optimizing a support vector machine on the data through iterative feature engineering. This data-driven approach reveals two important results: (i) a symbolic rule emerges that is independent of the algorithm, and (ii) the symbolic rule provides a deeper understanding of the fidelity boundary. Specifically, our dataset is composed of radial distribution functions from seven high-fidelity methods that cover wide ranges in the features (element, density, and temperature); high-fidelity results are compared with a simple pair-potential model to discover the nonlinear combination of the features, and the machine learning approach directly reveals the central role of atomic physics in determining accuracy.

Quantum anomalous Hall (QAH) insulator is the key material to study emergent topological quantum effects, but its ultralow working temperature limits experiments. Here, by first-principles calculations, we find a family of stable two-dimensional (2D) structures generated by lithium decoration of layered iron-based superconductor materials $\mathrm{Fe}X(X=\mathrm{S},\mathrm{Se},\mathrm{Te})$, and predict room-temperature ferromagnetic semiconductors together with large-gap high-Chern-number QAH insulators in the 2D materials. The extremely robust ferromagnetic order is induced by the electron injection from Li to Fe and stabilized by strong ferromagnetic kinetic exchange in the 2D Fe layer. While in the absence of spin-orbit coupling (SOC), the ferromagnetism polarizes the system into a half Dirac semimetal state protected by mirror symmetry, the SOC effect results in a spontaneous breaking of mirror symmetry and introduces a Dirac mass term, which creates QAH states with sizable gaps (several tens of meV) and multiple chiral edge modes. We also find a 3D QAH insulator phase featured by a macroscopic number of chiral conduction channels in bulk $\mathrm{LiOH}\text{−}\mathrm{Li}\mathrm{Fe}X$. The findings open new opportunities to realize novel QAH physics and applications at high temperatures.

We study the characteristic timescales of the fluctuating local moments in Hund’s metal systems for different degrees of correlation. By analyzing the dynamical spin susceptibility in the real-time domain, we determine the timescales controlling oscillation and damping of on-site fluctuations—a crucial factor for the detection of local moments with different experimental probes. We apply this procedure to different families of iron pnictides or chalcogenides, explaining the material trend in the discrepancies reported between experimental and theoretical estimates of their magnetic moments.

Network models for equilibrium integer quantum Hall (IQH) transitions are described by unitary scattering matrices that can also be viewed as representing nonequilibrium Floquet systems. The resulting Floquet bands have zero Chern number, and are instead characterized by a chiral Floquet winding number. This begs the question, How can a model without Chern number describe IQH systems? We resolve this puzzle by showing that nonzero Chern number is recovered from the network model via the energy dependence of network model scattering parameters. This relationship shows that, despite their topologically distinct origins, IQH and chiral Floquet topology-changing transitions share identical universal scaling properties.

Topological materials are expected to show distinct transport signatures owing to their unique band-inversion characteristic and band-crossing points. However, the intentional modulation of such topological responses through experimentally feasible means has yet to be explored in depth. Here, an unusual elevation of the anomalous Hall effect (AHE) is obtained in electron (Ni)-doped magnetic Weyl semimetals ${\mathrm{Co}}_{3-x}{\mathrm{Ni}}_x{\mathrm{Sn}}_2{\mathrm{S}}_2$, showing peak values in the anomalous Hall-conductivity, Hall-angle, and Hall-factor at a relatively low doping level of $x=0.11$. The separation of intrinsic and extrinsic contributions using the TYJ scaling model indicates that such a significant enhancement is dominated by the intrinsic mechanism of the electronic Berry curvature. Theoretical calculations reveal that compared with the Fermi-level shifting from electron filling, a usually overlooked effect of doping, that is, local disorder, imposes a striking effect on broadening of the bands and narrowing of the inverted gap, thus resulting in an elevation of the integrated Berry curvature. Our results not only realize an enhancement of the AHE in a magnetic Weyl semimetal, but also provide a practical design principle for modulating the bands and transport properties in topological materials by exploiting the local disorder effect from doping.

Electrons commonly couple through Fröhlich interactions with longitudinal optical phonons to form polarons. However, trions possess a finite angular momentum and should therefore couple instead to rotational optical phonons. This creates a polaronic trion whose binding energy is determined by the crystallographic orientation of the lattice. Here, we demonstrate theoretically within the Fröhlich approach and experimentally by photoluminescence emission that the bare trion binding energy (20 meV) is significantly enhanced by the phonons at the interface between the two-dimensional semiconductor ${\mathrm{MoS}}_2$ and the bulk transition metal oxide ${\mathrm{SrTiO}}_3$. The low-temperature binding energy changes from 60 meV in [001]-oriented substrates to 90 meV for [111] orientation, as a result of the counterintuitive interplay between the rotational axis of the ${\mathrm{MoS}}_2$ trion and that of the ${\mathrm{SrTiO}}_3$ phonon mode.

Detection and manipulation of excitations with non-Abelian statistics, such as Majorana fermions, are essential for creating topological quantum computers. To this end, we show the connection between the existence of such localized particles and the phenomenon of unitary subharmonic response (SR) in periodically driven systems. In particular, starting from highly nonequilibrium initial states, the unpaired Majorana modes exhibit spin oscillations with twice the driving period, are localized, and can have exponentially long lifetimes in clean systems. While the lifetime of SR is limited in translationally invariant systems, we show that disorder can be engineered to stabilize the subharmonic response of Majorana modes. A viable observation of this phenomenon can be achieved using modern multiqubit hardware, such as superconducting circuits and cold atomic systems.

We used a combination of polarized Raman spectroscopy and spin wave calculations to study magnetic excitations in the strong spin-orbit-coupled bilayer perovskite antiferromagnet ${\mathrm{Sr}}_3{\mathrm{Ir}}_2{\mathrm{O}}_7$. We observed two broad Raman features at $\sim 800$ and $\sim 1400{\mathrm{cm}}^{-1}$ arising from magnetic excitations. Unconventionally, the $\sim 800{\mathrm{cm}}^{-1}$ feature is fully symmetric ($A_{1g}$) with respect to the underlying tetragonal ($D_{4h}$) crystal lattice which, together with its broad line shape, definitively rules out the possibility of a single magnon excitation as its origin. In contrast, the $\sim 1400{\mathrm{cm}}^{-1}$ feature shows up in both the $A_{1g}$ and $B_{2g}$ channels. From spin wave and two-magnon scattering cross-section calculations of a tetragonal bilayer antiferromagnet, we identified the $\sim 800{\mathrm{cm}}^{-1}$ ($1400{\mathrm{cm}}^{-1}$) feature as two-magnon excitations with pairs of magnons from the zone-center $\mathrm{\Gamma }$ point (zone-boundary van Hove singularity $X$ point). We further found that this zone-center two-magnon scattering is unique to bilayer perovskite magnets which host an optical branch in addition to the acoustic branch, as compared to their single layer counterparts. This zone-center two-magnon mode is distinct in symmetry from the time-reversal symmetry broken “spin wave gap” and “phase mode” proposed to explain the $\sim 92\mathrm{meV}$ ($742{\mathrm{cm}}^{-1}$) gap in resonant inelastic x-ray spectroscopy magnetic excitation spectra of ${\mathrm{Sr}}_3{\mathrm{Ir}}_2{\mathrm{O}}_7$.

${\mathrm{SrTiO}}_3$ is an incipient ferroelectric that is believed to exhibit a prototype displacive, soft mode ferroelectric transition when subjected to mechanical stress or alloying. We use high-angle annular dark-field imaging in scanning transmission electron microscopy to reveal local polar regions in the room-temperature, paraelectric phase of strained ${\mathrm{SrTiO}}_3$ films, which undergo a ferroelectric transition at low temperatures. These films contain nanometer-sized domains in which the Ti columns are displaced. In contrast, these nanodomains are absent in unstrained films, which do not become ferroelectric. The results show that the ferroelectric transition of strained ${\mathrm{SrTiO}}_3$ is an order-disorder transition. We discuss the impact of the results on the nature of the ferroelectric transition of ${\mathrm{SrTiO}}_3$.

We determine which helical equilibria of an isotropic Kirchhoff elastic rod with clamped ends are stable and which are unstable. Although the set of all helical equilibria is parametrized by four variables, with an additional fifth parameter determined by the rod’s material, we show that only three of these five parameters are needed to distinguish between stable and unstable equilibria. We also show that the closure of the set of stable equilibria is star convex. With these results, we are able to compute and visualize the boundary between stable and unstable helices for the first time.

Unsharp measurements are increasingly important for foundational insights in quantum theory and quantum information applications. Here, we report an experimental implementation of unsharp qubit measurements in a sequential communication protocol, based on a quantum random access code. The protocol involves three parties; the first party prepares a qubit system, the second party performs operations that return both a classical and quantum outcome, and the latter is measured by the third party. We demonstrate a nearly optimal sequential quantum random access code that outperforms both the best possible classical protocol and any quantum protocol that utilizes only projective measurements. Furthermore, while only assuming that the involved devices operate on qubits and that detected events constitute a fair sample, we demonstrate the noise-robust characterization of unsharp measurements based on the sequential quantum random access code. We apply this characterization towards quantifying the degree of incompatibility of two sequential pairs of quantum measurements.