The intricate interplay between electronic and lattice degrees of freedom poses significant theoretical and experimental challenges in investigating the influence of electron-phonon scattering (EPS) on the anomalous Hall effect (AHE). In this study, by synergizing experimental measurements with theoretical calculations in $\mathrm{MnA}{\mathrm{l}}_{1-x}{\mathrm{Ga}}_x\mathrm{Ge}$, we observed an enhancement in the anomalous Hall conductivity (AHC) with a peak value of $922{\mathrm{\Omega }}^{-1}\mathrm{c}{\mathrm{m}}^{-1}$. Notably, we found that EPS plays a pivotal role in contributing to AHE in pristine MnAlGe, whereas this contribution diminishes gradually and ultimately disappears in Ga-doped systems. Raman spectroscopy revealed that the $A_{1g}$ and $B_{2g}$ modes undergo a shift towards lower frequencies in Ga-doped samples. Furthermore, Brillouin-light-scattering measurements demonstrated a marked reduction in the energy of the acoustic phonon branches. This phonon softening behavior is attributed to the weakened hybridization of the Al-Ge bond. Our findings illuminate a potential link between the impact of EPS on AHE and phonon softening.

Flat band systems have recently attracted significant attention due to their instability under small perturbations, which can lead to the stabilization of many exotic quantum phases. We study a trimer ladder which shows a middle flat band in the absence of onsite Coulomb interaction. We investigate the quantum phases of the Hubbard model on this geometry using exact diagonalization, density matrix renormalization group, and perturbation theory. We construct a quantum phase diagram in the plane of the next-nearest-neighbor hopping parameter $t_2$ and onsite Coulomb interaction $U$, revealing five distinct quantum phases. At low $U$ and moderate to high magnitude of $t_2$, the system exhibits metallic behavior, while at large $U$ and small magnitude of $t_2$, it transitions to a ferrimagnetic insulator phase, similar to those observed in certain trimer materials. In the small $t_2$ limit, the Fermi energy is in the flat band, leading to localization of the electrons within the trimer. At low $U$ and small magnitude of $t_2$, the flat band mechanism favors insulating ferrimagnetism, whereas at large $U$, ferrimagnetic states emerge from singlet dimer formation between neighboring sites of a trimer and an isolated corner spin, which connect ferromagnetically. The insulating cell spin density wave phase displays an up-up–down-down spin configuration due to competing nearest-neighbor hopping $t_1$. Interestingly, in moderate $U$ and $|t_2|>0.3$, the ground state behaves like metallic Tomonaga-Luttinger liquid.

In type-II/1 superconductors, the intervortex interaction has a potential minimum, resulting in an attractive force at certain distances. To better understand this unique vortex system, in situ observations in high-purity Nb have been performed using magneto-optical imaging with single-vortex resolution. We have dynamically visualized the behavior of the vortices during cooling, including clustering of attractively interacting single vortices, the hopping motion of vortices, the formation of an Abrikosov triangular lattice, and various degrees of disordered states with or without clusters. From the direct observations of clustering vortices, a conversion temperature for the boundary between type-II/2 and type-II/1 states is evaluated. The diverse vortex configurations arise from the interplay of the vortex-vortex interaction, the screening current, and the pinning potential landscape.

Paramagnetic color centers in hexagonal boron nitride $\left(h\text{−}\mathrm{BN}\right)$ exhibit great potential as fundamental units for quantum technologies. However, precise recognition of quantum emitters suitable for single-photon emission is elusive. Using hybrid density functional theory calculations, we demonstrate that the substitution of carbon at the nitrogen site along with the Stone-Wales defect in $h\text{−}\mathrm{BN}$ acts as a source of a single-photon emitter close to the 4 eV photoluminescence line. We estimate the Huang-Rhys (HR) factor is approximately 1.9, indicating a moderate electron-phonon coupling strength. The optical transition has a strong transition dipole moment of 0.94 $e$Å and a short radiative lifetime of 1.92 ns. Remarkably, the calculated HR factor and transition lifetimes are found to be in excellent agreement with experimental reports concerning carbon-related defects in $h\text{−}\mathrm{BN}$.

Water diffusion in silicate melt is an essential process for understanding the transport properties and dehydration kinetics of silicate melt. However, the fast liquid dynamics and interconversion of hydrous species pose a substantial challenge to both experimental and theoretical studies of water diffusion. We developed a bonding analysis method to unambiguously identify stable and transition-state hydrous species, and obtained their characteristic diffusion coefficients from restrained ab initio molecular dynamics simulations. We find that the stable species include a hydroxyl group, molecular water, and a trace amount of hydronium. Proton is only a transition-state species, but proton hopping dominates the overall water diffusion with a contribution over 60%, primarily through triggering the rotational diffusion of the O–H bond. Namely, the coupling of proton hopping and O–H bond rotation leads to fast water diffusion. The uncovered mechanism enables the construction of a water diffusion model based purely on thermodynamics, and extrapolating this model to temperatures below 2000 K aligns well with experimental observations.

Motivated by recent experimental progress in realizing Majorana zero modes (MZMs) using quantum dot systems, we investigate the diabatic errors associated with the movement of those MZMs. The movement is achieved by tuning time-dependent gate potentials applied to individual quantum dots, effectively creating a moving potential wall. To probe the optimized movement of MZMs, we calculate the experimentally accessible time-dependent fidelity and local density-of-states using many-body time-dependent numerical methods. Our analysis reveals that an optimal potential wall height is crucial to preserve the well-localized nature of the MZM during its movement. Moreover, we analyze diabatic errors in realistic quantum-dot systems, incorporating the effects of repulsive Coulomb interactions and disorder in both hopping and pairing terms. Additionally, we provide a comparative study of diabatic errors arising from the simultaneous versus sequential tuning of multiple gates during the MZMs movement. Finally, we estimate the timescale required for MZM transfer in a six-quantum-dot system, demonstrating that MZM movement is feasible and can be completed well within the qubit's operational lifetime in practical quantum-dot setups.

Recently, a novel probe to study symmetry breaking, known as entanglement asymmetry, has emerged and has been utilized to explore how symmetry is dynamically restored following quantum quenches. Interestingly, it has been shown that, in certain scenarios, greater initial symmetry breaking leads to faster restoration, akin to a quantum Mpemba effect. This study focuses on investigating the effect of mixed initial states and nonunitary dynamics on symmetry restoration. The mixedness of a state can arise from different sources. We consider dephasing or dissipative processes affecting initial pure states or unitary dynamics of initially thermal states. In the former case, the stationary state after the quench is independent of the initial configuration, resembling the phenomenology of the classical Mpemba effect. Investigating the XY spin chain model, through a combination of analytical calculations and numerical simulations, we identify the conditions for the occurrence of the quantum Mpemba effect. It turns out that this phenomenon still occurs in the presence of dissipation or at finite temperature, even though it will be eventually suppressed as the state becomes more mixed.

We investigate the $S=1/2$ antiferromagnetic Heisenberg model with a $3\times 3$ checkerboard lattice structure in a longitudinal magnetic field. By using the stochastic series expansion quantum Monte Carlo method, we obtain the properties of the nonplateau XY phase; 1/9, 3/9, 5/9, and 7/9 magnetization plateau phases; and fully polarized phase. Then, we determine the precise phase transition critical points belonging to the three-dimensional XY universality class through finite-size scaling. Moreover, we study the longitudinal and transverse dynamic spin structure factors of this model in different phases. For the nonplateau XY phase, the energy spectra present a gap between the low-energy gapless branch and the high-energy part due to the competition of magnetic field and interaction. The gapless branch can be described by the spin wave theory of the effective “block spin” model in the canted antiferromagnetic phase. In the magnetization plateau phase, we identify that the low-energy excitations arise from the localized disturbances within the sublattice and are capable of spreading in momentum space. The high-energy quasiparticles could be the multiplet excitations similar to the “triplon” in the dimerized system and “doublon” and “quarton” in the trimerized system. This paper offers theoretical insights and interpretations for the characteristics of the ground state and the inelastic neutron scattering spectra in two-dimensional quantum magnetic materials. Specifically, it focuses on materials with odd-spin configurations in the checkerboard unit cells under the influence of a longitudinal magnetic field.

We investigate a generalization of topological order from closed systems to open systems, for which the steady states take the place of ground states. We construct concrete lattice models with steady-state topological order, and characterize them by complementary approaches based on topological degeneracy of steady states, topological entropy, dissipative gauge theory, and relaxation dynamics. We take the topological degeneracy of steady states as the defining property of steady-state topological order, and study its stability using degenerate perturbation theory. We show that while the topological degeneracy is fragile in two dimensions, it is robust against perturbations in three and higher dimensions. We unveil how and why nontrivial steady-state topological order is always endowed with unusual relaxation dynamics. Particularly, the relaxation time is algebraically divergent in the thermodynamic limit, which is indicative of a gapless Liouvillian spectrum. It is shown that steady-state topological order remains definable in the presence of (Liouvillian) gapless modes: Whereas the (Liouvillian) level splitting between topologically degenerate steady states is exponentially small with respect to the system size, the Liouvillian gap between the steady states and the rest of the spectrum decays algebraically as the system size grows. We also investigate the topological phase transition to the trivial phase under additional noise, and find that the lifting of topological degeneracy is accompanied by gapping out the gapless modes. The topological phase transition is also diagnosed from the perspective of dissipative gauge theory, where the topologically ordered phase is identified as the deconfined phase and the trivial phase as the confined phase. Our paper offers a toolbox for investigating open-system topology of steady states.

We present an X-band and tunable high-frequency/high-field electron spin resonance (HF-ESR) study of single-crystalline ${\mathrm{Ca}}_{10}{\mathrm{Cr}}_7{\mathrm{O}}_{28}$, which constitutes alternating antiferromagnetic and ferromagnetic kagome bilayers. At high temperatures, a phonon-assisted relaxation process is evoked to account for the pronounced increase of the linewidth in an exchange-narrowing regime $(k_{\mathrm{B}}T\gg J)$. In contrast, at low temperatures $(k_{\mathrm{B}}T\lesssim J)$, a power-law behavior in line narrowing is observed. Our data reveal two distinct power-law regimes for the linewidth which crossover at $T^{*}\approx 7.5\mathrm{K}$. Notably, the intriguing evolution of the ESR linewidth in this alternating kagome bilayer system with opposite sign of exchange interactions highlights distinct spin dynamics compared to those in a uniform kagome antiferromagnet.

Recently, it has been shown that, in one-dimensional fermionic systems, close to band edges, the zero temperature conductance scales as $1/N^2$, where $N$ is the system length. This universal subdiffusive scaling of conductance at band edges has been tied to an exceptional point (EP) of the transfer matrix of the system that occurs at every band edge. Further, in the presence of bulk dephasing probes, this EP has been shown to lead to a counterintuitive superballistic scaling of conductance, where the conductance increases with $N$ over a finite but large regime of system lengths. In this work, we explore how these behaviors are affected by the order of the transfer matrix EP at the band edge. We consider a one-dimensional fermionic lattice chain with a finite range of hopping. Depending on the range of hopping and the hopping parameters, this system can feature band edges which correspond to arbitrarily higher order EPs of the associated transfer matrix. Using this system we establish in generality that, in the absence of bulk dephasing, surprisingly, the universal $1/N^2$ scaling of conductance is completely unaffected by the order of the EP. This is despite the fact that existence of transfer matrix EP is crucial for such behavior. In the presence of bulk dephasing, however, the phase coherence length, the extent of the superballisitic scaling regime, and the exponent of superballistic scaling all encode the order of the transfer matrix EP.

A theoretical framework for the nonequilibrium Green's function (NEGF) scheme is presented to account for the discrete nature of impurities doped in semiconductor nanostructures. The short-range part of the impurity potential is included as scattering potential in the self-energy due to spatially localized impurity scattering, and the long-range part of the impurity potential is treated as the self-consistent Hartree potential by coupling with the Poisson equation. The position-dependent impurity scattering rate under inhomogeneous impurity profiles is systematically derived so that its physical meaning is clarified. The position dependence of the scattering rate turns out that it is represented by the “center of mass” coordinates in the Wigner coordinates, rather than the real-space coordinates. Consequently, impurity scattering is intrinsically nonlocal in space. The proposed framework is applied to cylindrical thin wires under the quasi-one-dimensional approximation. We show explicitly how the discrete nature of impurities affects the transport properties such as electrostatic potential, local density of states, carrier density, scattering rates, and mobility.

Shortcuts to adiabaticity (STA) make the fast preparation of many-body states possible, circumventing the limitations of adiabatic strategies. We propose a fast STA protocol for generating interacting states in the Tomonaga-Luttinger liquid by counterdiabatic driving, stirring the dynamics with an auxiliary control field. To this end, we exploit the equivalence between the time-dependent Tomonaga-Luttinger liquid and an ensemble of quantum oscillators with driven mass and frequency. We specify the closed-form expression of the counterdiabatic control and demonstrate its efficiency in suppressing excitations.

Disordered forms of carbon are an important class of materials for applications such as thermal management. However, a comprehensive theoretical understanding of the structural dependence of thermal transport and the underlying microscopic mechanisms is lacking. Here we study the structure-dependent thermal conductivity of disordered carbon by employing molecular dynamics (MD) simulations driven by a machine-learned interatomic potential based on the efficient neuroevolution potential approach. Using large-scale MD simulations, we generate realistic nanoporous carbon (NP-C) samples with densities varying from 0.3 to 1.5 g ${\mathrm{cm}}^{-3}$ dominated by ${sp}^2$ motifs, and amorphous carbon (a-C) samples with densities varying from 1.5 to 3.5 g ${\mathrm{cm}}^{-3}$ exhibiting mixed ${sp}^2$ and ${sp}^3$ motifs. Structural properties including short- and medium-range order are characterized by the atomic coordination, pair correlation function, angular distribution function, and structure factor. Using the homogeneous nonequilibrium MD method and the associated quantum-statistical correction scheme, we predict a linear and a superlinear density dependence of thermal conductivity for NP-C and a-C, respectively, in good agreement with relevant experiments. The distinct density dependences are attributed to the different impacts of the ${sp}^2$ and ${sp}^3$ motifs on the spectral heat capacity, vibrational mean free paths, and group velocity. We additionally highlight the significant role of structural order in regulating the thermal conductivity of disordered carbon.

Principles behind antiferromagnetic spintronics often claim that an antiferromagnet (AF) cannot be manipulated by external magnetic fields and that domain walls (DWs) are highly mobile and do not suffer strong pinning while maintaining robustness during thermal fluctuations. Using dysprosium (Dy) as an example, we take the opposite view. The functionality of a helical AF in Dy uses two intrinsic properties of chiral DWs: their intrinsic magnetization and their freezing just below the Néel temperature. Experiments with Dy single crystal show that field cooling through the fluctuation regime converts a helical AF into a domain wall–dominated system with striking properties related with robustness of frozen chiral DWs. On the other hand, chiral DWs are easily controlled by external fields throughout the fluctuation regime.

We investigate the second-order photon correlation function in cavity-magnon systems, focusing on ferromagnetic and antiferromagnetic cavities within the ultrastrong coupling regime, and extending beyond the rotating-wave approximation. By deriving exact integral solutions for the second-order correlation function, we demonstrate that counter-rotating magnon-photon interactions induce quadrature squeezing in the cavity mode. Furthermore, we show that tuning the anisotropic magnon-cavity couplings enhances the squeezing effect by changing the level repulsion of the magnon-cavity photon hybrid mode without increasing the cavity photon occupation number. Our study reveals distinct quantum correlation behaviors in ferromagnetic and antiferromagnetic cavities: For ferromagnetic cavities, we show that squeezing increases with coupling strength asymmetry, whereas in the antiferromagnetic case, magnon modes with opposite chirality suppress quantum effects and impose a lower bound on correlation functions. These findings provide a pathway to optimize photon blockade for quantum information technology in magnon-cavity systems in the ultrastrong coupling limit.

We discuss the evolution of high-order Van Hove singularities (hoVHSs) that carry faster-than logarithmic divergences over a wide range of parameters in cupratelike electronic band dispersions. Numerical and analytic results give insight into the quantized value of the VHS power-law exponent $p_V$ and the transition between hoVHSs with different values of $p_V$. The cuprates are found to lie in the parameter regime where the amplitude of the hoVHS is not too large. Our study supports the idea that superconductivity in the cuprates occurs near a crossover between two different competing orders (antiferromagnetism and the density wave associated with the hoVHS), which is why high-temperature superconductivity is so rare.

Spin qubits in quantum dots provide a promising platform for realizing large-scale quantum processors since they have a small characteristic size of a few tens of nanometers. One difficulty of controlling, e.g., a few thousand qubits on a single chip is the large number of control lines. The crossbar control architecture has been proposed to reduce the number of control lines exploiting shared control among the qubits. Here we compile the surface code cycle to a pulse sequence that can be executed in the crossbar architecture. We decompose the quantum circuits of the stabilizer measurements in terms of native gates of the spin-qubit architecture. We provide a routing and scheduling protocol and construct a gate voltage pulse sequence for the stabilizer measurement cycle. During this protocol, coherent phase errors can occur on idle qubits, due to the operational constraints of the crossbar architecture. We characterize these crosstalk errors during the stabilizer measurement cycle and identify an experimentally relevant parameter regime where the crosstalk errors are below the surface code threshold. Our results provide design guidelines for near-term qubit experiments with crossbar architectures.