We theoretically investigate the electron tunneling in dual-gated bilayer graphene-based $n/p$ junctions. It is shown that a band gap is introduced by tuning the gate voltage, which modifies the pseudospin polarization and breaks anti-Klein tunneling at normal incidence. Specifically, when the pseudospin polarization vectors for the propagating and evanescent wave modes on the left and right regions of the junction are orthogonal, a revival of Klein tunneling is achieved. The Berry phase associated with Klein tunneling in dual-gated bilayer graphene is not limited to $\pi$ but varies with the junction parameters. Furthermore, the Klein tunneling is accompanied by a $\pi$ jump in the reflection phase around the normal incidence.

The complex valence band structure of bulk cuprous oxide necessitates going beyond the parabolic approximation to precisely estimate exciton binding energies. The same is true for excitons in cuprous oxide quantum wells, for which many effects have been obtained so far only qualitatively within a hydrogenlike two-band model. Here, we derive the complete Hamiltonian for excitons in cuprous oxide quantum wells based on the Luttinger-Kohn model, taking into account the full complex valence band structure. Symmetry properties of the system are discussed. Numerical results based on the diagonalization of the Hamiltonian using B-spline functions reveal the energy shifts and the lifting of degeneracies due to the nondiagonal coupling terms of the complex valence band. The relative oscillator strengths of the excitonic transitions induced by circularly polarized light are also calculated.

We explore the states of matter arising from the spontaneous symmetry breaking (SSB) of ${\mathbb{Z}}_2$ non-onsite symmetries. In one spatial dimension, we construct a frustration-free lattice model exhibiting SSB of a non-onsite symmetry, which features the coexistence of two ground states with distinct symmetry-protected topological (SPT) orders. We analytically prove the twofold ground-state degeneracy and the existence of a finite-energy gap. Fixing the symmetry sector yields a long-range entangled ground state that features long-range correlations among noninvertible charged operators. We also present a constant-depth measurement-feedback protocol to prepare such a state with a constant success probability in the thermodynamic limit, which may be of independent interest. Under a symmetric deformation, the SSB persists up to a critical point, beyond which a gapless phase characterized by a conformal field theory emerges. In two spatial dimensions, the SSB of 1-form non-onsite symmetries leads to a long-range entangled state (SPT soup)—a condensate of one-dimensional SPT along any closed loops. On a torus, there are four such locally indistinguishable states that exhibit algebraic correlations between local operators, which we derived via a mapping to the critical $O\left(2\right)$ loop model. This constitutes an intriguing example of ‘‘topological quantum criticality.’’

Developing reliable pseudopotentials for orbital-free density functional theory (OF-DFT), especially for transition metals, remains a significant challenge. In this study, we provide a theoretical framework for analyzing pseudization strategies for OF-DFT calculations. From the analysis arises a proposed pseudization method which involves constructing local pseudopotentials by targeting existing Kohn-Sham DFT pseudopotentials through an optimized effective potential procedure. We produce four distinct sets of local pseudopotentials and evaluate their accuracy and transferability on the set of transition metal elements. Our results indicate a substantial improvement over previously available pseudopotentials. Although current OF-DFT functionals still only reach a qualitative accuracy for transition metals, our newly developed pseudopotentials provide a rigorous framework for further methodological advancements.

Recently, there has been considerable excitement surrounding the promising realization of high-spin Kitaev material, such as the quasi-2D compound ${\mathrm{CrI}}_3$ and ${\mathrm{CrGeTe}}_3$. However, the stability of quantum spin liquids (QSL) against single-ion anisotropy (SIA) in these materials and the global quantum phase diagram of the extended spin-3/2 Kitaev model with finite SIA remain unclear. In this study, we perform large-scale density matrix renormalization group (DMRG) to explore the quantum phase diagram of the generalized spin-3/2 Kitaev-Heisenberg (K-H) model accompanied with SIA $A_c$. In the $A_c=0$ limit, the spin-3/2 K-H model exhibits a quantum phase diagram similar to that of a spin-1/2 system, including two QSLs around antiferromagnetic and ferromagnetic Kitaev models. For models with finite $A_c$, we map out the quantum phase diagram around two Kitaev points and observe distinct types of in-plane vortex orders developed from these two QSL phases. Interestingly, a series of nearly degenerate vortex configurations is discovered in each vortex phase. Using linear spin-wave theory, we demonstrate that these vortex configurations can be understood as a consequence of the quantum correction on a continuous family of degenerate classical states.

We report angle-resolved photoemission spectroscopy (ARPES) studies combined with $\mathrm{DFT}+\mathrm{DMFT}$ calculations to confirm that the magnetic ordering vector transition from $\mathrm{Q}=(1/2,0,0)$ to $\mathrm{Q}=(1/3,0,0)$ in the metallic triangular antiferromagnets ${\mathrm{Co}}_{1/3\pm \epsilon }{\mathrm{TaS}}_2$ ($\epsilon \approx 0.007$) is induced by the electronic structure change in the system. The ARPES-measured Fermi surface (FS) maps of ${\mathrm{Co}}_{0.325}{\mathrm{TaS}}_2$ show two hexagonal and one circular holelike FSs around $\mathrm{\Gamma }$, which matches well with the triple-Q state by taking into account the contribution of nesting vectors occurring between Co $3d$ and Ta $5d$ orbitals. In the case of ${\mathrm{Co}}_{0.340}{\mathrm{TaS}}_2$, a new electron pocket around K appears, and the FS geometry changes as a result of the correlation effect of ${\mathrm{Co}}_4{\mathrm{S}}_{18}$ tripods forming in the system. The magnetic susceptibility calculations based on the charge-self-consistent $\mathrm{DFT}+\mathrm{DMFT}$ band structures and the random phase approximation indicate that the most stable magnetic ordering vector (1/2,0,0) split into (1/6,0,0) and (1/2,0,0), which is consistent with the magnetic phase transition around $x=1/3$ in ${\mathrm{Co}}_x{\mathrm{TaS}}_2$.

We investigate electron pairing in a super clean kagome superconductor ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$ with a residual resistivity ratio (RRR) of 290. Using the dilution-refrigerator-based scanning tunneling microscopy (STM) at the Synergetic Extreme Condition User Facility (SECUF), we find that the pairing gap exhibits chiral 2 × 2 modulations, and their chirality can be controlled by magnetic field training. We introduce nonmagnetic impurities to observe the complete suppression of 2 × 2 pairing modulations in presence of persistent 2 × 2 charge order. This nonmagnetic pair-breaking effect provides phase-sensitive evidence for pair-density-wave (PDW)-induced pairing modulations. Our results support switchable chiral 2 × 2 PDW in this super clean kagome superconductor.

We demonstrate that including the second viscosity of an electron gas in the hydrodynamic model allows for highly accurate modeling of the optical response of heavily doped semiconductors. In our setup, which improves resonance visibility compared to previous approaches, plasmon resonances become more distinct, allowing for a detailed analysis of the underlying physics. With advanced fitting techniques based on a physics-informed cost function and a tailored optimization algorithm, we obtain a close agreement between simulations and experimental data across different sample thicknesses. This enhanced resonance visibility, combined with our integrated approach, shows that key parameters such as doping level and effective electron mass, as well as the second viscosity of the electron gas, can be retrieved from a single optical measurement. The spatial dispersion taken into account in the hydrodynamic framework is essential for accurately describing the optical response of plasmonic materials in this frequency range and is likely to become a standard modeling approach.

Bernstein modes—hybrid magnetoplasmon excitations arising from the coupling between cyclotron motion and collective oscillations in two-dimensional electron systems—offer direct access to nonlocal electrodynamics. These modes can exhibit rich nonlinear behavior akin to strong-coupling phenomena in cavity quantum electrodynamics, but reaching the nonlinear regime has remained experimentally challenging. Here we report the observation of nonlinear Bernstein modes in graphene using terahertz excitation with near-field enhancement from embedded metallic contacts. Photoresistance spectroscopy reveals sharp resonances at $B_c/2$ and $B_c/3$ that saturate at radiation intensities nearly an order of magnitude lower than the cyclotron resonance. We ascribe this to strong local heating of the electron gas due to resonant excitation of high-amplitude Bernstein magnetoplasmons, associated with a combination of the field-concentration effect of the near field and plasmonic amplification that is resonantly enhanced in the region of Bernstein gaps. Polarization-resolved measurements further confirm the near-field origin: Bernstein resonances are insensitive to circular helicity but strongly depend on the angle of linear polarization, in sharp contrast to the cyclotron resonance response. Our results establish graphene as a platform for nonlinear magnetoplasmonics, opening opportunities for strong-field manipulation of collective electron dynamics, out-of-equilibrium electron transport, and solid-state analogues of cavity quantum electrodynamics.

α-${\mathrm{Li}}_3\mathrm{N}$ is a promising $\mathrm{L}{\mathrm{i}}^{+}$ superionic conductor for battery applications due to its high ionic conductivity. The superionic behavior emerges with the breakdown of anisotropy in $\mathrm{L}{\mathrm{i}}^{+}$ diffusion. This study investigates the role of different Li sites in the hexagonal layered structure in influencing the ionic transport using machine-learned molecular dynamics simulation. We found that below 600 K, the Li at $2c$ Wyckoff site contribute dominantly to diffusion in the $\mathit{ab}$ plane. However, at elevated temperatures, Li at both the Wyckoff sites ($2c$ and $1b$) becomes equally mobile, leading to three-dimensional superionic behavior. Further, we identified that the superionic transition is associated with the strong anharmonicity in low-energy phonon modes dominated by $\mathrm{L}{\mathrm{i}}^{+}$ dynamics. We find that this transition leads to a marked reduction in lattice thermal conductivity, highlighting the role of strongly anharmonic low-energy phonons in suppressing thermal transport.

Magnetic chirality describes the fixed correspondence between polarization and rotation of noncollinear spin twists. It remains a fundamental challenge in determining the chirality of Néel-twisted nanometric spin textures. This work presents a theoretical framework for determining the chirality of Néel-type spin twists via magnetic force microscopy (MFM). By modeling the magnetostatic interaction between a nanometric magnetic tip and the stray field of a two-dimensional magnetic film, our analytical model and numerical simulations demonstrate that the magnetic fields generated by distinct moment components of a left-handed Néel-type spin twist mutually cancel, resulting in a vanishing phase shift. In contrast, a right-handed twist exhibits a twofold enhancement in the phase shift. The influence of magnetic anisotropy on this phase-shift contrast is also discussed. Our findings provide a critical advancement for skyrmion imaging using conventional MFM and establish guidelines for experimental chirality determination.

Magnetic solitons such as skyrmions and bimerons show great promise for both fundamental research and spintronic applications. Stabilizing and controlling topological spin textures in atomically thin van der Waals (vdW) materials has gained tremendous attention due to high tunability, enhanced functionality, and miniaturization. Here, we present an efficient spin-spiral approach based on first-principles calculations, a method for mapping magnetic interactions from collective models onto arbitrary lattice symmetries, such as hexagonal and honeycomb lattices. Using atomistic spin models parametrized from first principles, we predict the emergence of multiple topological spin textures in an all-magnetic vdW heterostructure ${\mathrm{Fe}}_3{\mathrm{GeTe}}_2/{\mathrm{Cr}}_2{\mathrm{Ge}}_2{\mathrm{Te}}_6$ (FGT/CGT)–an experimentally feasible system. Interestingly, the FGT layer favors out-of-plane magnetization, whereas the CGT layer prefers in-plane magnetocrystalline anisotropy. Néel-type nanoscale skyrmions are formed at zero field in the FGT layer due to interfacial Dzyaloshinskii-Moriya interaction (DMI), while nanoscale bimerons and antibimerons can co-exist in the CGT layer by the interplay between exchange frustration and DMI. Using our collective approach, we reveal significant discretization effects in hexagonal and honeycomb lattices. In particular, we demonstrate that the lifting of geometric exchange frustration on the honeycomb lattice significantly affects soliton barriers and pinning energetics. These fundamental results not only highlight the importance of spin simulations in discrete models for topological magnetism, especially in 2D materials, but may also help to pave the way for solitonic devices based on atomically thin vdW heterostructures.

Rhombohedral ${\mathrm{CoTiO}}_3$ is a Dirac-type antiferromagnet with unique nodal magnetic dynamics, a strong Zeeman-phonon effect, and multiple spin-orbital excitations. The intricate interaction between these excitations makes it difficult to precisely understand its properties. We report the observation of strong spin-phonon coupling for several phonon modes, as well as the Zeeman splitting of the degenerate phonon modes with $E_g$ symmetry. These effects were observed in magnetic fields applied perpendicular to and within the $ab$-plane, and they evidence a phonon magnetic moment reaching up to a giant value of 1.63 ${\mu }_B$. Some of these modes experience extremely strong coupling with spin-orbital excitations of the ${\mathrm{Co}}^{2+}$ ions, manifested as avoided crossings, which leads to an underestimated magnitude of the phonon splitting at low fields. Both acoustic and optical magnon branches were observed in the antiferromagnetic phase, along with a two-magnon continuum within the 10–22 meV range, closely reflecting the magnon density of states. Observation of new magnetic modes above the spin-orientation transition at 17 T challenges the applicability of the flavor wave model to the spin dynamics in ${\mathrm{CoTiO}}_3$. Strong renormalization of the magnon and phonon modes (including zone-folded ones) suggests a low-field spin-orientation transition around 1 T within the $ab$-plane.

A fundamental understanding of ultrafast charge transfer dynamics is essential for the rational design of functional optoelectronic and photovoltaic devices. However, the underlying microscopic mechanisms of the charge transfer process at the heterojunction interface remain unclear, particularly regarding the specific role of the interfacial dipole moment and external electric field (EEF). Here, we systematically investigate the ultrafast interfacial charge transfer of $\mathrm{Hf}{\mathrm{S}}_2$/$\mathrm{Mo}X\mathrm{Se}$ ($X=\mathrm{S}$, Se) heterostructures using ab initio nonadiabatic molecular dynamics. The results demonstrate that the $\mathrm{Hf}{\mathrm{S}}_2/{\mathrm{MoSe}}_2$ heterostructure exhibits strong nonadiabatic coupling, and ultrafast interlayer hole and electron transfer occurring within 116 and 136 fs, respectively. Notably, the hole transfer dynamics are significantly suppressed in the symmetry-broken $\mathrm{Hf}{\mathrm{S}}_2$/MoSSe heterostructure, which is primarily attributed to the interfacial dipole substantially modifying both the charge distribution and interlayer coupling strength. Furthermore, within the $\mathrm{Hf}{\mathrm{S}}_2/{\mathrm{MoSe}}_2$ system, we elucidated the asymmetric modulation mechanism of EEFs on interlayer charge transfer dynamics: a negative EEF significantly slows down charge transfer, while a positive EEF accelerates electron transfer but suppresses hole transfer. The elucidation of this specific mechanism provides important theoretical insights for developing high-performance optoelectronic devices based on two-dimensional transition metal dichalcogenide heterostructures.

First-principles real-time time-dependent density-functional theory (rt-TDDFT) calculations reveal the existence of ballistic photocurrents generated by Coulomb scattering, which has not previously been considered as a mechanism for the bulk photovoltaic effect. With monolayer GeS as an example, it is predicted that ballistic currents can be comparable to shift currents under experimentally accessible conditions.

We show that periodically time-modulating the Dzyaloshinskii-Moriya interaction (DMI) in a two-dimensional magnon insulator may induce a topological phase transition that results in the presence of robust edge modes. To this end, we study a square lattice of spins interacting via an XXZ Heisenberg model with a ferromagnetic longitudinal coupling and antiferromagnetic transverse coupling, as well as the aforementioned time-modulated DMI. The topologically protected edge states of this system are composed of coherent superpositions of single-magnon excitations and two-magnon bound states. Furthermore, we show that the chirality of the edge states can be controlled by adjusting the relative phase for the drive on the DMI associated with nearest neighbors in the $x$ and $y$ directions.

Motivated by the experiment by Budden et al. [Nat. Phys. 17, 611 (2021)], who observed signatures of long-lived photoinduced superconductivity, we develop an accurate analytical and computational approach to nonequilibrium superconductivity following a quench. We consider the BCS-Holstein model, which includes both integrable local electron-electron interactions and integrability-breaking electron-phonon coupling. We develop the Keldysh-Eliashberg theory on the Kadanoff-Baym contour, which enables us to describe nonequilibrium dynamics of the superconductor. We consider a quench in interactions, which results in a dynamic transition from the initial superconducting state to a normal thermal state in the end of the evolution. It is shown that the dynamics contain two stages: The early-time integrable behavior, involving coherent oscillations of the superconducting order parameter, crosses over to the late-time ergodic dynamics exhibiting a thermal decay into an equilibrium state. In the former regime, our computational approach both reproduces exact analytical results on the integrable dynamics of the order parameter (obtained for the zero-temperature initial state) and generalizes those to the case of an initial thermal state. The method also succeeds in describing both integrable-to-thermalizing crossover and the late-time thermal decay, which is shown to be consistent with the time-dependent Ginzburg-Landau theory (with the exponential decay time dependent on the density of quasiparticle excitations). We observe the electron distribution function approaching the Fermi-Dirac thermal distribution at final stages. The details of two-time nonequilibrium dynamics depend on the density of quasiparticles in the initial state and the integrability-breaking parameters, which under certain conditions may result in a long-lived transient superconductivity consistent with experiment.

We develop a method to construct simple and explicit variational approximations for the ground state of Kitaev's honeycomb model with a nontrivial ${\mathbb{Z}}_2$ flux configuration consisting of a pair of visons on neighboring plaquettes. The method consists of retaining only the largest singular values of the generator of the transformation between the vison pair and flux-free ground states. We compare physical quantities calculated using the approximate state to those obtained by extrapolating the results of exact diagonalization of finite lattices, finding them to be in very good agreement. We discuss ways to extend the method to more complicated flux configurations.

We formulate a path-integral Monte Carlo algorithm for simulating lattice systems consisting of fictitious particles governed by generalized exchange statistics. This method, initially proposed for continuum systems, introduces a continuous parameter $\xi$ in the partition function that interpolates between bosonic $(\xi =1)$ and fermionic $(\xi =-1)$ statistics. We generalize this approach to discrete lattice models and apply it to the two-dimensional Hubbard model of fictitious particles, including the Bose- and Fermi-Hubbard models as special cases. By combining reweighting and $\xi$-extrapolation techniques, we access both half-filled and doped regimes. In particular, we demonstrate that the method remains effective in strongly correlated, doped systems, offering a distinct advantage by naturally operating in the canonical ensemble. Our results validate the applicability of the fictitious-particle framework to lattice models and establish it as a promising, complementary tool for investigating strongly interacting fermionic systems.