We investigate theoretically field-induced switching of magnetic topology in a nanodisk-shaped sample of noncentrosymmetric dipolar magnet in which the Dzyaloshinskii-Moriya interaction that stabilizes an antiskyrmion with $N_{\mathrm{sk}}=+1$ and the magnetic dipole interaction that stabilizes a skyrmion with $N_{\mathrm{sk}}=-1$ are in keen competition, where $N_{\mathrm{sk}}$ is the skyrmion number. Our micromagnetic simulations demonstrate that the competition offers a unique opportunity to switch magnetic textures with distinct magnetic topology among the antiskyrmion $(N_{\mathrm{sk}}=+1)$, elliptical skyrmion $(N_{\mathrm{sk}}=-1)$, and nontopological bubble $(N_{\mathrm{sk}}=0)$ in a deterministic manner by application of magnetic fields parallel to the sample plane. By calculating time and spatial profiles of energy contributions from respective interactions and magnetic anisotropy, we clarify the physical mechanism and properties of the observed field-induced topology switching phenomena. Our findings are expected to provide useful insights in the spintronic application of topological magnetism.

Two-dimensional superconductors have garnered significant attention due to their exceptional quantum properties, particularly tunable superconductivity, which holds great potential for advanced quantum technologies. In this study, first-principles calculations reveal two stable transition metal mononitride monolayers—1T- and $1H\text{−}{\mathrm{Mo}}_2{\mathrm{N}}_2$—featuring chemically distinct Mo- and N-terminated surfaces. Electron-phonon coupling calculations predict the superconducting transition temperatures $\left(T_{\mathrm{c}}\right)$ of $\sim 13.6$ K for the 1T phase and $\sim 13.5$ K for the 1H phase. The coupling between Mo $d_{z^2}$ orbital electrons at the Fermi level and out-of-plane acoustic phonon modes associated with Mo atoms is identified as a key contributor to superconductivity. Hydrogenation on the Mo-terminated surface boosts $T_{\mathrm{c}}$ to 25.4 K in 1T phase, driven by the increase of Mo $d_{z^2}$ electronic states at the Fermi level and the softening of the out-of-plane acoustic mode induced by the activation of Mo-H bond stretching vibrations. In contrast, hydrogenation on the N-terminated surface suppresses superconductivity due to the inhibition of out-of-plane Mo vibrations. Furthermore, double-sided hydrogenation on both surfaces reduces $T_{\mathrm{c}}$ to 16.9 K in the 1T phase and 8.2 K in the 1H phase. These findings provide valuable insights into tunable superconductivity in two-dimensional materials through targeted site-dependent hydrogenation.

Layertronics is an emerging field that effectively controls various physical behaviors of two-dimensional (2D) materials and their artificial stacks. While most prior works focused on modulating the interlayer interaction and layer-dependent properties, here we investigate layer-dependent disorder (either Anderson type or magnetic exchange field) effects, which could naturally occur in realistic 2D layered materials. We show that disorder could effectively toggle the spatial symmetry statistically. While the spatially homogeneous disorder tends to enhance the spatial symmetry, layer-dependent disorder is spatially inhomogeneous and could reduce such symmetry in a statistical manner, especially breaking the intact centrosymmetry $\mathcal{P}$. We further characterize such a $\mathcal{P}$ breaking by the emergence of shift current, an intrinsic bulk photovoltaic effect arising from the position mismatch between the valence and conduction band centers under linearly polarized light irradiation. This is rooted from momentum space shift and is illustrated by tight-binding model simulations and first-principles calculations on the $\mathcal{P}$-symmetric bilayer transition metal dichalcogenide (for on-site energy disorder) and trilayer antiferromagnetic ${\mathrm{CrI}}_3$ (for magnetic exchange disorder) as exemplary platforms. The layer-dependent disorder is permissible experimentally, especially under the substrate effect. This work expands the scope of layertronics and clarifies the symmetry control of layer-disorder effect.

Resonant spectroscopies, which involve intermediate states with finite lifetimes, provide essential insights into collective excitations in quantum materials that are otherwise inaccessible. However, theoretical understanding in this area is often limited by the numerical challenges of solving Kramers-Heisenberg-type response functions for large-scale systems. To address this, we introduce a multishifted biconjugate gradient algorithm that exploits the shared structure of Krylov subspaces across spectra with varying incident energies, effectively reducing the computational complexity to that of linear spectroscopies. Both mathematical proofs and numerical benchmarks confirm that this algorithm substantially accelerates spectral simulations, achieving constant complexity independent of the number of incident energies, while ensuring accuracy and stability. This development provides a scalable, versatile framework for simulating advanced spectroscopies in quantum materials.

The low hole mobility in wide-bandgap semiconductors remains a critical bottleneck for complementary and high-power electronic devices. Prior first-principles predictions suggested a monotonic increase of over 200% in hole mobility under biaxial tensile strain on the (0001) plane in GaN [Phys. Rev. Lett. 123, 096602 (2019)]. Here, using density functional theory combined with Boltzmann transport formalism, we demonstrate a nonmonotonic, V-shaped modulation of hole mobility as a function of such strain: the overall hole mobility decreases and reaches a minimum at a strain of 0.4–0.5%, then increases at higher strain levels. Our results reveal no enhancement of the in-plane hole mobility under strain up to 1.6%. This nonmonotonic behavior arises from a concurrent evolution of the hole effective masses and hole-phonon scattering rates, both driven by a strain-induced valence-band order inversion. These findings offer critical insights into the interplay between strain and hole transport in wide-bandgap materials and highlight the necessity of precise strain engineering for device performance optimization.

We present a theoretical study of the exchange interaction in a system of spatially disordered magnetic moments. A typical example of such a system is an impurity semiconductor whose magnetic properties are associated with the exchange interaction of the impurity atoms. In this study, we consider the case of antiferromagnetic exchange interaction, which we describe by the Heisenberg Hamiltonian. To calculate the magnetic properties of the disordered system, we employ the joint density of states method. Our calculations demonstrate good quantitative agreement with the experimental dependence of the Si:P magnetic susceptibility on temperature in a wide range of impurity concentrations and temperatures. The obtained results may be important for a deeper understanding of the metal-dielectric transition nature.

In this work, a thorough exploration has been carried out to unravel the role of electron-phonon interaction (EPI) in a Bernevig-Hughes-Zhang quantum spin Hall (QSH) insulator subjected to a time-periodic step drive. It is observed that upon inclusion of the EPI, the system demonstrates emergent Floquet QSH phases and several topological phase transitions thereof, mediated solely by the interaction strength. Such transitions are indicated by the discontinuities in the projected spin Chern number. Furthermore, to employ a topological invariant that can characterize the system in an energy-resolved manner, a spectral localizer ($\mathcal{SL}$) is introduced, which distinctly ascertains the nature of the (zero or $\pi$) edge modes obtained within the corresponding topological gap. Quite intriguingly, we also observe the emergence of phases hosting a topological zero ($\pi$) energy gap while its $\pi$ (zero) energy sector is gapless. With the Chern number being found to be deficient in characterizing such coexistent phases, a real-space Chern marker (following the $\mathcal{SL}$ prescription) computed by us further provides support to such a gapless Floquet topological scenario. Our results may be realized in optical setups that may underscore the importance of EPI-induced Floquet features.

The growth morphology and electronic properties of epitaxial Ag(111) films on ${\mathrm{MoS}}_2\left(0001\right)$ surfaces have been investigated using selected-area low-energy electron diffraction, low-energy electron microscopy, and density functional theory. The growth dynamics of Ag(111) films evolve with thickness, unveiling an intriguing growth mechanism. The films display strained pseudomorphic growth for lower coverages, while relaxed flat Ag(111) films form for nominal coverages exceeding 2.5 ML, following the Stranski-Krastanov growth mode. The strain relaxation leads to the nucleation of two-dimensional Ag islands with steep-edged flat (111) tops, while for higher nominal coverages, the island morphology evolves to rooflike islands with a flat Ag(111) top and faceted sides. The side facets were identified as {100}, {110}, and $\left\{\overline{1}11\right\}$ planes by reciprocal space mapping using facet diffraction spots. With increasing thickness, these islands coalesce, eventually covering the entire ${\mathrm{MoS}}_2$ surface. Further, the variations in the surface work function and unoccupied density of states for different film coverages are studied, providing insights into the relationship between strain, surface morphology, and electronic properties. These films' structural, morphological, and electronic state evolutions as a function of the annealing temperatures have also been detailed. Notably, annealing above 400 $°\mathrm{C}$ leads to forming fully discrete Ag islands while retaining the characteristic rooflike morphology, highlighting the high thermal stability of these facet planes.

In bilayer graphene, the exact energy levels of quantum dots (QDs) can be derived from the four-component continuum Hamiltonian. Here, we study the QD energy levels with approximate equations and compare them with the exact levels. The starting point of our approach is the four-component continuum model, and the QD is defined by a continuous potential well in a uniform magnetic field. Using some simple arguments, we demonstrate realistic regimes where approximate QD equations can be derived. Interestingly, these approximate equations can be solved semianalytically, in the same context as a single-component Schrödinger equation. The approximate equations provide valuable insight into the physics with minimal numerical effort compared with the four-component QD model. We show that the approximate QD energy levels agree very well with the exact levels in a broad range of parameters and find realistic regimes where the relative error is vanishingly small.

We demonstrate a thermo-optic switching of nonmonotonic Casimir potential with a local minimum, termed quantum trap, for Au plate immersed in ethanol and located above Teflon-coated Au substrate. Beyond a critical temperature of 420 K, the quantum trap is switched to monotonic attraction, due to the reversal of relative rankings of ethanol's and Teflon's dielectric functions. The effect originates from thermal expansion-induced decrease of ethanol's dielectric function, rather than temperature-related electronic transitions of interacting materials. In the case of barrierlike Casimir potential with a local maximum for suspended Teflon plate, while the barrier height reduces with temperature, no switching is allowed due to the stronger retardation effect at relatively farther unstable equilibria. The thermo-optic effect provides a viable route to control interobject interaction in liquid environment and modulate dynamic properties of nonmonotonic Casimir systems.

A powerful way to guarantee the absence of a sign problem in determinantal quantum Monte Carlo simulations is imposing a particular type of antiunitary symmetries. It is shown that these same symmetries give rise to constraints on correlation functions, which can be used to identify local operators whose correlations upper bound those of a large class of physically relevant operators, including for example superconducting order parameters. Our results also help understand why it is difficult to realize generic finite-momentum orders in sign problem free models.

Topological phases with high Chern numbers (HCNs) have garnered significant interest in research on the quantum anomalous Hall effect. However, topological states with Chern numbers $C>2$ remain scarce in both theoretical and experimental studies. In this paper, we introduce a mechanism for achieving arbitrary Chern numbers in spin-orbit coupled systems. This mechanism leverages phase-controlled Floquet engineering to induce high-order spin flips. Notably, the realization of unbounded HCNs is contingent upon the phase relationship in the temporally modulated spin-flip coefficient. Furthermore, to implement this mechanism, we propose a self-designed dual-set optical Raman lattice that drives atomic transitions, thereby demonstrating a quantum simulator capable of accessing the $C\ge 5$ regime. Our findings not only overcome the current limits on achievable Chern numbers, but also open alternative avenues for exploring different topological phases, with potential applications in quantum technologies such as topological quantum computation and quantum simulation.

Understanding the dynamic properties of uniform electron gas (UEG) is important for numerous applications ranging from semiconductor physics to exotic warm dense matter. In this work, we apply the maximum entropy method (MEM), as implemented by Thomas Chuna et al., J. Phys. A Math. Theor. 58, 335203 (2025), to ab initio path integral Monte Carlo (PIMC) results for the imaginary-time correlation function $F(q,\tau )$ to estimate the dynamic structure factor $S(q,\omega )$ over an unprecedented range of densities at the electronic Fermi temperature. To conduct the MEM, we propose to construct the Bayesian prior $\mu$ from the PIMC data. Constructing the static approximation leads to a drastic improvement in $S(q,\omega )$ estimate over using the simpler random phase approximation (RPA) as the Bayesian prior. We present results for the strongly coupled electron liquid regime with $r_s=50,\cdots ,200$, which reveal a pronounced roton-type feature and an incipient double peak structure in $S(q,\omega )$ for intermediate wave numbers at $r_s=200$. We also find that our dynamic structure factors satisfy known sum rules, even though these sum rules are not enforced explicitly. To verify our results, we show that our MEM estimates converge to the RPA limit at higher densities and weaker coupling $r_s=2$ and 5. Further, we compare with two different existing results at intermediate density and coupling strength $r_s=10$ and 20, and we find good agreement with more conservative estimates. Combining all of our results for $r_s=2,5,10,20,50,100,200$, we present estimates of a dispersion relation that show a continuous deepening of its minimum value at higher coupling. An advantage of our setup is that it is not specific to the UEG, thereby opening up new avenues to study the dynamics of real warm dense matter systems based on cutting-edge PIMC simulations in future works.

We study nonreciprocal signatures of Josephson current in a quantum dot (QD)-based Josephson junction that comprises two periodically driven Kitaev chains (KCs) coupled with an intervening QD. The simultaneous breaking of the inversion symmetry and the time-reversal symmetry, indispensable for the Josephson diode effect (JDE), is achieved solely via the two Floquet drives that differ by a finite phase, which eventually results in a nonreciprocal current and hence yields a finite JDE. It may be noted that the Floquet Majorana modes generated at both the far ends of the KCs (away from the QD) and adjacent to the QD junctions mediate the Josephson current owing to a finite superconducting (SC) phase difference in the two KCs. We calculate the time-averaged Josephson current and inspect the tunability of the current-phase relation to ascertain the diode characteristics. The asymmetric Floquet drive also manifests an anomalous Josephson current signature in our KC-QD-KC Josephson junction. Furthermore, additional control over the QD energy level can be achieved via an external gate voltage that renders flexibility for the diode to act as an SC switching device. Tuning different system parameters, such as the chemical potential of the KCs, Floquet frequency, the relative phase mismatch of the drives, and the gate voltage, our model shows a maximum rectification $\sim 70\%$. Summarizing, in our study, we provide an alternative scenario, replacing the traditional usage of an external magnetic field and spin-orbit coupling effects in a Josephson diode via asymmetrically driven Kitaev leads that entail Majorana-mediated transport.

Manipulating polaritons in van der Waals (vdW) materials offers a unique platform for advancing nanophotonic applications and enhancing our comprehension of strong light-matter interactions. Here, two-dimensional (2D) polaritonic Smith-Purcell radiation (SPR) that arises from the interaction between grazing-incidence electron beams and vdW materials patterned with a grating structure is investigated. We demonstrate that both isotropic graphene plasmons and hyperbolic phonon polaritons in $\alpha$-phase molybdenum trioxide ($\alpha \text{−}{\mathrm{MoO}}_3$) can be excited efficiently by incident electron beams. Moreover, by adjusting the grating periodicity while keeping the operation frequency constant, the emission direction of the resulting polaritons can be precisely tuned. Our modeling of SPR generation on the surface of 2D vdW materials not only reveals the feasibility of SPR in low-dimensional systems, but also provides a versatile approach for nanoscale manipulation of infrared light.

Nonrelativistic spin splitting in unconventional antiferromagnets has garnered much attention for its promising spintronic applications and open fundamental questions. Here, we uncover a unique even-parity spin texture in chiral noncollinear antiferromagnets, exemplified using a kagome lattice. We consider two distinct types of electrons in the system: one with Schrödinger-like dispersion and the other exhibiting Dirac-like behavior. Remarkably, we show that, for both electron types, this spin texture induces an exotic coexistence of opposite-spin singlet and equal-spin triplet Cooper pairs with finite momentum when proximity coupled to conventional superconductors. The triplet pairing arises from the intrinsic spin rotation of the antiferromagnet and does not require net magnetization or spin-orbit coupling. Moreover, we identify a tunable phase difference between singlet and triplet pairings, controllable through junction orientation. This mixed pairing state can be experimentally probed via damped oscillations in order parameters and $0\text{−}\pi$ transitions in Josephson junctions. Additionally, we analyze the effect of out-of-plane spin canting, elucidating its role in generating spin-polarized supercurrents, and discuss ${\mathrm{Mn}}_3\mathrm{Ga}$ and ${\mathrm{Mn}}_3\mathrm{Ge}$ to test our predictions.