The coherent transport of time-resolved ultrafast excitations in nanoelectronic interferometers is expected to exhibit an interesting interplay between the interferences and the time-dependent drive. However, the typical frequencies required to unlock this physics are in the THz range, making its observation challenging. In this work, we consider the propagation of the excitation generated by ultrashort voltage pulses through a small quantum dot, a system which we argue can display similar physics at significantly lower frequencies. We model the system with a single resonant level connected to two infinite electrodes subjected to a time-dependent voltage bias. For short pulses, we predict that the behavior of the dot contrasts sharply with the long-pulse (adiabatic) limit: The current actually oscillates with the amplitude of the voltage pulse. In the ultrafast limit, we predict that the current can even be negative, i.e., flow against the voltage drop. Our results are obtained by a combination of two approaches that are in quantitative agreement: explicit analytical expressions in the ultrafast and ultraslow limits and exact numerical simulations. We discuss the applicability of our findings and conclude that this system should be within reach of existing experimental platforms.

The interplay of the excitoniclike polariton, polariton, and photoniclike polariton coherent states in mass-imbalanced electron-hole systems within optical microcavities is theoretically examined. Utilizing the unrestricted Hartree-Fock approximation, we derive a set of self-consistent equations that evaluate the excitonic and photonic order parameters in a two-band electronic model, accounting equally for both electron-hole Coulomb attraction and light-matter coupling. Analyzing the competition among these condensate order parameters reveals a complex phase structure of coherent states in the ground state. As the mass imbalance is reduced, we observe a transition from a normal disordered electron-hole-photon system to excitoniclike, polariton, and ultimately photoniclike polariton condensation states. The distinct features of these robust condensates can be identified in the momentum distribution of the electron-hole pair amplitude and the photonic density, as well as in the wave-number-resolved photoemission spectra of electrons, holes, and photons. Increasing the excitation density further expands the range of condensation states. Additionally, lowering the mass imbalance leads to the emergence of quantum coherent bound states prior to the formation of robust condensates, which are evidenced by the static and dynamical excitonic and photonic susceptibility functions.

Controlling magnetism with an electric field and polarization with a magnetic field at room temperature is critical for the application of multiferroic materials, and the big challenge remains due to the basic contradiction between ferroelectric polarization and magnetism. Here, we find the realization of this regulation in a magnetoelectric (ME) hexaferrite $\mathrm{B}{\mathrm{a}}_{0.5}\mathrm{S}{\mathrm{r}}_{2.5}\mathrm{C}{\mathrm{o}}_2\mathrm{F}{\mathrm{e}}_{24}{\mathrm{O}}_{41}$ ceramic, which achieves magnetization reversal under a low electric field (∼0.5 kV/cm) and exhibits stable regulation of polarization under a low magnetic field (∼1.5 mT). We have further observed four nonvolatile ME coefficient curves with magnetic fields induced by different poling processes. Together with changing DC magnetic field direction, eight states can be realized at a low magnetic field, which can be used as a four-state or even eight-state memory prototype. Moreover, the phase transformation is likely to exist in $\mathrm{B}{\mathrm{a}}_{0.5}\mathrm{S}{\mathrm{r}}_{2.5}\mathrm{C}{\mathrm{o}}_2\mathrm{F}{\mathrm{e}}_{24}{\mathrm{O}}_{41}$ at 350 K. The ME effects are the result of the inverse Dzyaloshinskii-Moriya interaction (DMI), which plays a primary role in the modulation of ME effects under low fields, while additional p-d hybridization serves as a significant factor dominating the ME effects across all of the applied magnetic fields, including high fields.

In a heavy-fermion system, the competition between the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction and the Kondo effect determines the ground-state properties, including superconductivity, magnetic orderings, and non-Fermi-liquid states. However, the temperature-dependent development of this competition remains unclear, particularly within the framework of ferromagnetic ground states. Here, the electronic structure and heavy quasiparticle band properties are exhaustively studied in $\mathrm{CeNiS}{\mathrm{b}}_2$, a prototypical ferromagnetic Kondo lattice, using high-resolution angle-resolved photoemission spectroscopy. Our measurements reveal the three-dimensional electronic structure and Fermi surface topologies in $\mathrm{CeNiS}{\mathrm{b}}_2$. The discrepancy of the quasiparticle bands along the Γ-$M$ direction indicates band-dependent hybridization between the $f$ electrons and conduction electrons ($c\text{−}f$ hybridization), which may arise from differences in the conduction-band properties. The intensity of the quasiparticle band increases monotonically with decreasing temperature and deviates from the Kondo-like behavior at low temperature. This evolution provides a comprehensive picture of how the RKKY interaction and the Kondo effect develop and influence the behavior of $f$ electrons across the temperature range. Our experimental results offer a spectroscopic study of the quasiparticle band and its temperature-dependent evolution in $\mathrm{CeNiS}{\mathrm{b}}_2$, which may be crucial for understanding the underlying physics in heavy fermion compounds.

We present results for evolution of the Fermi surfaces under a variation of number density and displacement field for spin- and valley-polarized states in Bernal bilayer graphene using a realistic form of the electronic dispersion with trigonal warping terms. Earlier studies without trigonal warping have found discrete half-metal and quarter-metal states with full spin and/or valley polarization and complete depletion of some of the Fermi surfaces. We show that when trigonal warping terms are included in the dispersion, partially polarized states with large but noncomplete polarization and with both majority and minority carriers present, emerge at small doping, as seen in the experimental data. We show the results when the intervalley and intravalley interactions are equal as well as when they are unequal.

Ferroelectricity, the Rashba effect, and band topology have been individually explored in various two-dimensional (2D) materials. Investigating their mutual couplings offers exciting opportunities for understanding complex physics and unlocking new functionalities. However, the coexistence and modulation of all three properties within a single 2D system remain rare. In this work, we unveil a mechanism to achieve this synergy through interlayer sliding in 2D $M\mathrm{B}{\mathrm{i}}_2\mathrm{T}{\mathrm{e}}_4$ ($M$ = Ge, Sn, Pb) bilayers, in which a centrosymmetric $M\mathrm{B}{\mathrm{i}}_2\mathrm{T}{\mathrm{e}}_4$ monolayer intrinsically manifests as a second-order topological insulator. Our findings reveal that bilayer $M\mathrm{B}{\mathrm{i}}_2\mathrm{T}{\mathrm{e}}_4$ exhibits ferroelectricity combined with giant Rashba spin splitting (with ${\alpha }_R$ of ∼2.2 eV Å) and protected one-dimensional edge states under distinctive and robust stacking orders. As well, interlayer sliding enables modulation of both ferroelectric polarization and Rashba spin textures and facilitates transitions between topological insulator and second-order topological insulator phases. Our results provide pathways for the innovation of next-generation multifunctional electronic nanodevices with the ability to combine ferroelectric, spintronic, and topotronic technologies.

Mobility edges (MEs) constitute the energies separating the localized states from the extended ones in disordered systems. Going beyond this conventional definition, recent proposal suggests an ME which separates the localized and multifractal states in certain quasiperiodic systems, dubbed the anomalous mobility edges (AMEs). In this study, we propose a quasiperiodic system with solvable mobility edges that hosts both the conventional and anomalous mobility edges under proper conditions. We show that, with increase in quasiperiodic potential strength, the system first undergoes a delocalization to localization transition through an ME of conventional type. Surprisingly, with further increase in potential, we find that a major fraction of the localized states at the middle of the spectrum turn multifractal in nature. Such unconventional behavior in the spectrum results in two AMEs, which continue to exist even for stronger quasiperiodic potential. We numerically obtain the signatures of the coexisting MEs complement it through analytical derivation using Avila's global theory. In the end we provide important signatures from the wave-packet dynamics.

The emergence of topologically nontrivial flat bands in moiré materials provides an opportunity to explore the interplay between topological physics and correlation effects, leading to the recent experimental realization of interacting topological phases, e.g., fractional Chern insulators. In this work, we propose a general mechanism of band inversion induced by the moiré Brillouin zone folding of atomic bands for engineering topological minibands in moiré materials. We illustrate this mechanism via two classes of model Hamiltonians, namely the Rashba model and the Bernevig-Hughes-Zhang (BHZ) model, under the moiré superlattice potentials. We find moiré minibands with the nontrivial band topology, including the ${\mathbb{Z}}_2$ number, mirror Chern number, and fragile topology, and the topological phase diagram is constructed for these moiré models. A general theory based on band representations in the morié Brillouin zone is also developed for a generalization of this mechanism to all 2D plane groups. Possible experimental realizations of our model Hamiltonian are discussed.

Motivated by the recent experimental progress in exploring the use of a nitrogen-vacancy (NV) center in diamond as a quantum computing platform, we propose schemes for fast and high-fidelity entangling gates on this platform. Using both analytical and numerical calculations, we demonstrate that synchronization effects between resonant and off-resonant transitions may be exploited such that spin-flip errors due to strong driving may be eliminated by adjusting the gate time or the driving field. This allows for fast, high-fidelity entangling operations between the electron spin and one or several nuclear spins. We investigate a two-qubit system where the NV center comprises a ${}^{15}\mathrm{N}$ atom and a qubit-qutrit system for the case of a ${}^{14}\mathrm{N}$ atom. In both cases, we predict a complete suppression of off-resonant driving errors for two-qubit gates when addressing the NV electron spin conditioned on states of nuclear spins of the nitrogen atom of the defect. Additionally, we predict fidelities $>0.99$ for multiqubit gates when including the surrounding ${}^{13}\mathrm{C}$ atoms in the diamond lattice in the conditioned logic.

Characteristics of magneto-electro-elastic effects in a diamond with negatively charged nitrogen vacancy centers are calculated analytically. It is predicted that strains or the external electric field can cause the onset of projections of the magnetic moment of those vacancies perpendicular to the applied magnetic field. It is shown how spins of those vacancies produce the anisotropy of the electric permittivity of a diamond, which depends on the external magnetic field and temperature. The temperature- and magnetic-field-dependent renormalization of elastic modules of a diamond caused by spin quadrupole moments of negatively charged nitrogen vacancy centers is calculated. The predicted effects can be important in the practical use of diamond nanocrystals with color vacancies as local sensors in modern nanoelectroncs.

Axions, initially proposed to solve the strong $CP$ problem, have recently gained attention in condensed matter physics, particularly in topological insulators. However, detecting axion dynamics has proven challenging, with no experimental confirmations to date. In this paper, we identify the surface of magnetic topological insulators as an ideal platform for observing axion dynamics. The vanishing bulk gap at the surface allows for order $O\left(1\right)$ variations in the axion field, making the detection of axionlike phenomena more feasible. In contrast, these phenomena are strongly suppressed in the bulk due to the small magnetic exchange gap. We investigate two-photon decay as a signature of axion dynamics and calculate the branching ratio using a perturbative approach. Our findings reveal that the photon flux emitted from the surface is in plane and orders of magnitude larger than that from the bulk, making it detectable with modern microwave technology. We also discuss potential material platforms for detecting axion two-photon decay and strategies to enhance the signal-to-noise ratio.

The magnetic coupling between perpendicular magnetic anisotropy (PMA) and in-plane magnetic anisotropy (IMA) films plays a crucial role in achieving field-free magnetization switching driven by spin-orbit torque (SOT). In this study, we report an even-symmetric Hall magnetoresistance signal in IMA/PMA multilayers, which is attributed to the planar Hall effect and the emergence of an out-of-plane secondary easy axis by interlayer magnetic coupling. Field-free magnetization switching is achieved in the IMA/PMA multilayers through interlayer magnetic coupling. Additionally, shifts in SOT-driven magnetization switching curves are observed, arising from the nonparallel arrangement between the magnetic moments of the IMA layer and the applied pulse current. These findings deepen the understanding of interlayer coupling in IMA/PMA systems and hold significant implications for the development of SOT-based spintronic devices.

Superconducting high-entropy alloys (HEAs) present a unique platform for studying the effect of disorder, composition, and crystal structure on superconducting pairing. In this study, we present a comprehensive bulk and microscopic investigation of the rarely observed equiatomic hexagonal HEA Nb-Mo-Ru-Re-Ir using magnetization, resistivity, heat capacity, and muon spin relaxation and rotation ($\mu \mathrm{SR}$) measurements. Our findings confirm bulk type-II superconductivity with a transition temperature of 4.63(2) K and a high upper critical field. Heat capacity and transverse-field $\mu \mathrm{SR}$ data reveal conventional $s$-wave superconductivity, while zero-field $\mu \mathrm{SR}$ results suggest the preservation of time-reversal symmetry in the superconducting state. These findings provide valuable insights into the superconducting pairing mechanism in disordered multicomponent systems.

Banded random matrices were introduced as a more realistic alternative to full random matrices for describing the spectral statistics of heavy nuclei. Initially considered by Wigner, they have since become a paradigmatic model for investigating level statistics and the localization-delocalization transition in disordered quantum systems. In this work, we demonstrate that, despite the absence of short-range energy correlations, weak long-range energy correlations persist in the nonergodic phase of banded random matrices. This result is supported by our numerical and analytical studies of quantities that probe both short- and long-range energy correlations, namely, the spectral form factor, level number variance, and power spectrum. We derive the timescales for the onset of spectral correlations (ramp) and for the saturation (plateau) of the spectral form factor. Unexpectedly, we find that in the nonergodic phase, these timescales decrease as the bandwidth of the matrices is reduced. We also show that the high-frequency behavior of the power spectrum of energy fluctuations can distinguish between the nonergodic and ergodic phases of the banded random matrices.

The transition-metal pentatelluride $\mathrm{HfT}{\mathrm{e}}_5$ exhibits unique topological properties and anomalous transport behaviors at low temperatures, with the underlying physical mechanism hypothesized to be linked to the formation of charge density waves (CDWs). However, current experimental studies lack direct evidence to confirm the presence of CDWs in $\mathrm{HfT}{\mathrm{e}}_5$. Here, using ultrafast coherent phonon spectroscopy, we investigate the bosonic quasiparticle dynamics of $\mathrm{HfT}{\mathrm{e}}_5$ and identify two low-energy coherent oscillations in the sub-THz range (∼0.55 THz and ∼0.72 THz), which show significant frequency softening as the critical temperature ($T^{*}\sim 75\mathrm{K}$) is approached. Excluding the possibility of acoustic phonons through pump wavelength- and fluence-dependent time-domain oscillation analysis, we propose that these modes are likely collective excitations of amplitude modes of CDWs, driven by a minimally nested wave vector in $\mathrm{HfT}{\mathrm{e}}_5$. Our findings provide experimental evidence for the potential existence of CDW order in $\mathrm{HfT}{\mathrm{e}}_5$ from a nonequilibrium perspective, which may offer insight into the microscopic origins of its exotic physical properties.

We study the dynamic structure factor $S(k,\omega )$ of the spin-1/2 chain with long-range, power-law decaying unfrustrated (sign-alternating) Heisenberg interactions $J_r\sim {(-1)}^{r-1}{r}^{-\alpha }$ by means of stochastic analytic continuation (SAC) of imaginary-time correlations computed by quantum Monte Carlo (QMC) calculations. We do so in both the long-range antiferromagnetic (AFM, for $\alpha \lesssim 2.23$) and quasi-long-range-ordered (QLRO, for $\alpha \gtrsim 2.23$) ground-state phases, employing different SAC parametrizations of $S(k,\omega )$ to resolve sharp edges characteristic of fractional quasiparticles and sharp peaks expected with conventional quasiparticles. In order to identify the most statistically accurate parametrization, we apply a newly developed cross-validation method as a “model selection” tool. We confirm that the spectral function contains a power-law divergent edge in the QLRO phase and a very sharp (likely $\delta$-function) magnon peak in the AFM phase. From our SAC results, we extract the dispersion relation in the different regimes of the model, and in the AFM phase we extract the weight of the magnon pole. In the limit where the model reduces to the conventional Heisenberg chain with nearest-neighbor interactions, our $S(k,\omega )$ agrees well with known Bethe-ansatz results. In the AFM phase the low-energy dispersion relation is known to be nonlinear, ${\omega }_k\sim k^z$, and we extract the corresponding dynamic exponent $z\left(\alpha \right)$, which in general is somewhat above the form obtained in linear spin-wave theory. We also find a significant continuum above the magnon peak. This study serves as a benchmark for SAC and QMC studies of systems with a transition from conventional to fractionalized quasiparticles.

In this work, the properties of $\mathrm{B}{\mathrm{a}}_9\mathrm{F}{\mathrm{e}}_3{\mathrm{S}}_{15}$ have been studied via magnetism, electrical transport, and specific heat measurements. The crystal structure mainly consists of face-sharing octahedral $\mathrm{Fe}{\mathrm{S}}_6$ chains with an interchain distance of 9.2320 Å, demonstrating a strongly quasi-one-dimensional (1D) character. $\mathrm{B}{\mathrm{a}}_9\mathrm{F}{\mathrm{e}}_3{\mathrm{S}}_{15}$ is a semiconductor with a band gap of 562 meV and its electrical transport property is dominated by $p$ electrons. The semiconducting behavior is kept under the highest pressure up to 62 GPa. The long-range spin order (LRSO) transition has been observed with $T_{\mathrm{C}}\sim 8.8$ K. The neutron diffraction experiments provide evidence that $\mathrm{B}{\mathrm{a}}_9\mathrm{F}{\mathrm{e}}_3{\mathrm{S}}_{15}$ hosts ferrimagnetic spin chains with the spins parallel to (110) and the spin assignment of $\mathrm{F}{\mathrm{e}}_2\uparrow \mathrm{F}{\mathrm{e}}_1\downarrow \mathrm{F}{\mathrm{e}}_2\uparrow$. $T^{0.5}$ dependence on the magnetic contribution to the specific heat has been observed above $T_{\mathrm{C}}$, indicating the natural property of the 1D ferrimagnetic spin chain. In addition, the magnetic susceptibility deviates from the Curie-Weiss law far above $T_{\mathrm{C}}$, and the LRSO transition only causes a small kink in the specific heat curve; these imply that short-range spin orders have formed above $T_{\mathrm{C}}$ because of the strong intrachain spin coupling. Also, it is revealed that the ordered moment is reduced by over 40% in $\mathrm{B}{\mathrm{a}}_9\mathrm{F}{\mathrm{e}}_3{\mathrm{S}}_{15}$, which is indicative of the spin partially ordered state below $T_{\mathrm{C}}$ and implies the existence of strong quantum fluctuation in the reduced dimension system. $\mathrm{B}{\mathrm{a}}_9\mathrm{F}{\mathrm{e}}_3{\mathrm{S}}_{15}$ should be a unique example to further study the intrinsic properties of an ideal ferrimagnetic spin chain.

Hydride superconductors are considered promising candidates for achieving high-temperature superconductivity, yet the ultrahigh pressures required for their stabilization present significant challenges for practical applications. In this study, a series of Cs-In-H ternary hydrides were systematically investigated at 50 GPa using crystal-structure prediction methods. Four thermodynamically stable phases and one metastable high-symmetry structure, $\mathrm{C}{\mathrm{s}}_3\mathrm{In}{\mathrm{H}}_7$, were identified. Notably, $\mathrm{C}{\mathrm{s}}_3\mathrm{In}{\mathrm{H}}_7$ exhibits a superconducting transition temperature of 81 K at 41 GPa. In the $Pm-3m-\mathrm{C}{\mathrm{s}}_3\mathrm{In}{\mathrm{H}}_7$ structure, the quasi-${\mathrm{H}}_2$ molecular units form the alloy framework, serving as the primary contributors to its superconducting properties, while the body-centered single H atom plays a pivotal role in regulating the overall performance. This high-temperature superconductivity can be attributed to the Fermi-surface grid contributed by In-H near the Fermi level, as well as the phonon softening induced by the nesting effect. This work offers a promising direction for the development of low-pressure hydride superconductors and lays a solid foundation for future experimental investigations.