The Dzyaloshinskii-Moriya interaction (DMI), which originates from spin-orbit coupling and relies on broken inversion symmetry, is recognized as a key ingredient in forming magnetic skyrmions. However, most two-dimensional (2D) magnets exhibit inversion symmetry; therefore, the DMI is suppressed. Here, we propose a strategy to induce large DMI via lithium absorption on the surface of 2D magnets, an experimentally feasible approach. Using first-principles and atomistic spin simulations, we predict the formation of nanoscale skyrmions in lithium-decorated monolayer ${\mathrm{Fe}}_3{\mathrm{GeTe}}_2$ by imposing small out-of-plane magnetic fields ($B_z$). Notably, we find very large skyrmion energy barriers of more than 300 meV at $B_z=0.4\mathrm{T}$, comparable to those observed in ferromagnet/heavy-metal interfaces. The origin of these unique skyrmions is attributed to the competition between strong DMI, exchange frustration, and small magnetocrystalline anisotropy energy. We further show that the lifetimes of metastable skyrmions exceed 1 h for temperatures up to 75 K.

The recent achievement of superconductivity in ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_{7-\delta }$ with transition temperatures exceeding 40 K in thin films under compressive strain and 80 K in bulk crystals under high pressure opens new avenues for research on high-temperature superconductivity. The realization of superconductivity in thin films requires delicate control of growth conditions, which presents significant challenges in the synthesis process. Furthermore, the stability of superconducting ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_{7-\delta }$ films is compromised by oxygen loss, which complicates their characterization. We introduce an effective recycling protocol that involves oxygen removal in a precursor phase followed by ozone-assisted annealing, which restores superconducting properties. By tuning the oxygen content, we construct an electronic phase diagram that highlights oxygen addition as a potential analog to hole doping via La substitution with Sr, providing insights into the doping mechanism and guiding future material optimization.

Magic-angle twisted bilayer graphene (TBG) with its flat bands provides a rich platform for exploring emergent electronic orders. Similarly, periodically buckled monolayer graphene (MLG) has been proposed as a tunable alternative for realizing flat bands. Here, we investigate the combined effect of buckling and twisting in bilayer graphene. We find that periodic buckling in large-angle TBG initially enhances band flattening compared to monolayer graphene, but for sufficiently strong buckling, it instead increases the band dispersion. This occurs because of both the presence of interlayer coupling, which reduces the in-plane kinetic energy, and the opening of a gap at the Dirac point resulting from inversion-symmetry breaking. Additionally, we find that buckling-induced band flattening competes with twist-induced band flattening. While the former breaks sublattice symmetry, generating a sublattice polarization, the latter prefers to preserve it. This prevents buckling from generating even flatter bands at the magic angle. Nevertheless, we find that buckled TBG can exhibit flatter bands than pristine TBG over a wide range of twist angles, with a flatness similar to that of pristine magic-angle TBG.

We present numerically exact inchworm quantum Monte Carlo results for the real-time dynamics of the spin polarization in the sub-Ohmic spin-boson model at finite temperature. We focus in particular on the localization and coherence behavior of the model, extending our previous study at low temperature [Goulko et al., Phys. Rev. Lett. 134, 056502 (2025)]. As the temperature increases, the system becomes less localized and less coherent. The loss of coherence, which is controlled by two independent mechanisms—a smooth damping-driven crossover and a sharp frequency-driven transition—exhibits a nontrivial temperature dependence. While both types of coherence loss occur at lower coupling in the high temperature regime, the frequency exhibits a sharper drop at high temperatures and this drop is observed for all values of the sub-Ohmic exponent, in contrast to the zero-temperature case. We discuss the full temperature-dependent dynamical phase diagram of the system and the interplay between coherence and localization across a wide range of physical parameters.

The energy levels and optical transitions of tetrahedral core/shell InP/ZnSe quantum dots (QDs) are investigated by means of multiband $\mathrm{k}·\mathrm{p}$ theory. Despite the ${\overline{T}}_d$ symmetry relaxing spherical selection rules, the near-band-edge excitonic spectrum is reminiscent of that obtained for spherical nanocrystals. Exceptions appear in large (red-emitting) QDs, where transitions violating the (quasi)angular momentum selection rule ($\mathrm{\Delta }L=0,\pm 2$) are observed, and the ground state does not become dark ($P_{3/2}$-like). Valence band coupling is important in determining the symmetry, degeneracy, and energy of hole states, with split-off holes playing a greater role than in CdSe QDs. The ($1S_e$-like) electron ground state is localized in and around the InP core, far in energy from the excited states, which are more spread into the ZnSe shell. This makes exciton Coulomb interactions be mostly perturbative. Electrons remain largely localized by the InP core even in negative trions, despite electron-electron repulsions. At the same time, the asymmetry between Coulomb attractions and repulsions leads to negative (positive) trions being bound (antibound) by tens of meV. The biexciton binding energy switches from positive to negative, depending on the QD size. The interplay among the different physical factors we examine renders the intrinsic optical response of InP/ZnSe QDs distinct from both core-only InP QDs and conventional II-VI core/shell QDs.

Recent work on Majorana-bound states in semiconductor-superconductor hybrid structures has elucidated the key role of unintentional (and unknown) disorder (producing low-energy Andreev-bound states) in the system, which is detrimental to the emergence of Majorana-carrying topological superconductivity artificially engineered through the combination of superconductivity, Zeeman spin splitting, and Rashba spin-orbit coupling. In particular, the disorder must be smaller than the superconducting gap for the appearance of Majorana modes, but the disorder-induced appearance of subgap Andreev-bound states suppresses the Majorana modes. We theoretically investigate, as a function of disorder, the normal state ballistic transport properties of nanowires with and without superconductors in order to provide guidance on how to experimentally estimate the level of disorder. Experimentally, the superconductivity is suppressed simply by rotating the magnetic field appropriately, so both physics can be studied in the same setup. In particular, the presence of spin-orbit coupling and Zeeman splitting produces a helical gap in the 1D electronic band structure, which should have clear signatures in ballistic transport unless these signatures are suppressed by disorder and/or Fabry-Pérot resonances associated with the finite wire sizes. Our work provides a benchmarking of when and what signatures of the putative helical gap (which is essential for the emergence of Majorana modes by leading to a single Fermi surface) could manifest in realistic nanowires. We also provide results in the presence of a superconductor (with the Zeeman field oriented such that the nanowire remains normal) to make contact with a recent experiment. A main conclusion is that the system could actually possess a Majorana-carrying helical gap even if the normal state ballistic transport results are ambiguous or agnostic about such a gap.

At ambient conditions, NiO is a prototypical antiferromagnetic correlated insulator. According to conventional Mott physics, applied pressure is expected to reduce the band gap and induce an insulator-to-metal transition. However, first-principles simulations consistently predict metallization pressures around 1 TPa, far exceeding the experimentally observed value of approximately 240 GPa. This significant discrepancy highlights a limitation in the prevailing theoretical understanding. Here, we employ the method that incorporates pressure-dependent electronic correlations parameters to reinvestigate this longstanding issue by systematically evaluating the roles of electronic structure, magnetic order, and crystal structure. Our simulations suggest that the pressure-dependent electronic correlations, coupled with a potential structural transition constitute the primary driving force of the insulator-metal transition at experimentally observed pressures. Incorporating pressure-dependent electronic correlations allows accurate determination of the band gap of insulating state and the prediction of a $B1\text{−}B2$ structural transition near the experimentally reported pressure. Moreover, this structural transition triggers a crystal-field inversion that partially fills the $t_{2\mathrm{g}}$ orbitals, leading to metallic behavior.

In this work, we present a systematic investigation of the electronic structures, band topology, and intrinsic spin Hall effect (SHE) in the layered MAX carbides $M_{n+1}\mathrm{Al}{\mathrm{C}}_n (M=\mathrm{Nb},\mathrm{Ta};n=1,2,3)$ and explore the correlation effects on the SHE. Our results show that this family of materials exhibits Dirac-band-crossing features near the Fermi level $E_F$ and forms nodal lines in the absence of spin-orbit coupling (SOC). When the SOC is included, the Dirac band crossings are fully gapped, resulting in nontrivial $Z_2$ topological invariants (1;000) with a pair of surface states on the (001) plane. Notably, the multiple gapped Dirac points contribute to locally strong spin Berry curvatures, which lead to large spin Hall conductivities (SHCs) and spin Hall angles (0.02–0.62 at $E_F$) for $\mathrm{T}{\mathrm{a}}_{n+1}\mathrm{Al}{\mathrm{C}}_n$ ($n=1,2,3$). Moreover, we also elucidate the impact of the Hubbard $U$ correction on SHCs. Our findings suggest that $\mathrm{T}{\mathrm{a}}_{n+1}\mathrm{Al}{\mathrm{C}}_n$ ($n=1,2,3$) might represent intriguing layered $Z_2$ topological metals with superior charge-to-spin conversion efficiency.

Rhombohedral or ABC-stacked multilayer graphene hosts a correlated magnetic ground state at charge neutrality, making it one of the simplest systems to investigate strong electronic correlations. We investigate this ground state in multilayer graphene structures using the Hubbard model in a distance–dependent Slater-Koster tightbinding framework. We show that by using a universal Hubbard-$U$ term, we can accurately capture the spin polarization predicted by hybrid density functional theory calculations for both hexagonal (ABA) and rhombohedral (ABC) stackings. Using this $U$ value, we calculate the magnetic moments of three to eight layers of ABC and ABA graphene multilayers. We demonstrate that the structure and magnitude of these magnetic moments are robust when heterostructures are built from varying numbers of ABC and ABA multilayers. By applying different types of mechanical distortions, we study the behavior of the magnetism in graphene systems under uniaxial strain and pressure. Our results establish a computationally efficient framework to investigate correlation-driven magnetism across arbitrary stacking configurations of graphite polytypes.

Electron-photon hybrid systems serve as ideal light-matter interfaces with broad applications in quantum technologies. These systems are typically operated dynamically under nonequilibrium conditions, giving rise to coupled electronic and photonic currents. Understanding the joint fluctuation behavior of these currents is essential for assessing the performance of light-matter interfaces that rely on electron-photon correlations. Here, we investigate the full counting statistics of coupled electronic and photonic currents in an experimentally feasible hybrid system composed of a double quantum dot coupled to an optical cavity. We employ the framework of quantum Lindblad master equation which is augmented with both electronic and photonic counting fields to derive their joint cumulant generating function (CGF)—a treatment that differs significantly from existing studies, in which either electron or photon statistics are typically focused on separately. We reveal that the ratio between photonic and electronic currents, as well as their variances, can deviate from an expected quadratic scaling law in the large electron-photon coupling regime. Furthermore, we demonstrate that conventional modelings of photonic dissipation channels in quantum master equations must be modified to ensure that the joint CGF satisfies the fluctuation symmetry enforced by the fluctuation theorem. Our results advance the understanding of joint fluctuation behaviors in electron-photon hybrid systems and may inform the design of efficient quantum light-matter interfaces.

We report a rich anisotropic magnetic phase diagram of ${\mathrm{Na}}_3{\mathrm{Co}}_2{\mathrm{SbO}}_6$, a previously proposed cobaltate Kitaev candidate, based on field- and temperature-dependent magnetization, specific heat, and magnetocaloric effect studies. At low temperatures, our experiments uncover a low-lying $j_{\text{eff}}=\frac{1}{2}$ state with an antiferromagnetic (AFM) ground state and pronounced in-plane versus out-of-plane anisotropy. The experimentally identified magnetic phases are theoretically characterized through classical Monte Carlo simulations within an extended Kitaev-Heisenberg model with additional ring exchange interactions. The resulting phase diagram reveals a variety of exotic field-induced magnetic phases, including double-$\mathbf{q}, \frac{1}{3}$-AFM, zigzag, and vortex phases.

A dissipationless supercurrent state in superconductors can be destroyed by thermal fluctuations. Thermally activated phase slips provide a finite resistance of the sample and are responsible for dark counts in superconducting single-photon detectors. The activation barrier for a phase slip is determined by a space-dependent saddle-point (instanton) configuration of the order parameter. In the one-dimensional wire geometry, such a saddle point has been analytically obtained by Langer and Ambegaokar in the vicinity of the critical temperature $T_c$ and for arbitrary bias currents below the critical current $I_c$. In the two-dimensional geometry of a superconducting strip, which is relevant for photon detection, the situation is much more complicated. Depending on the ratio $I/I_c$, several types of saddle-point configurations have been proposed, with their energies being obtained numerically. We demonstrate that the saddle-point configuration for an infinite superconducting film at $I\to I_c$ is described by the exactly integrable Boussinesq equation solved by Hirota's method. The instanton size is $L_x\sim \xi {(1-I/I_c)}^{-1/4}$ along the current and $L_y\sim \xi {(1-I/I_c)}^{-1/2}$ perpendicular to the current, where $\xi$ is the Ginzburg-Landau coherence length. The activation energy for thermal phase slips scales as $\mathrm{\Delta }{F}^{\text{2D}}\propto {(1-I/I_c)}^{3/4}$. For sufficiently wide strips of width $w\gg L_y$, a half instanton is formed near the boundary, with the activation energy being 1/2 of $\mathrm{\Delta }{F}^{\text{2D}}$.

Elements exhibiting three stable current plateaus enable ternary logic, reducing interconnect load, and simplifying decision-making compared to binary logic. We show that a single off-resonant, linearly polarized optical drive can produce such plateaus in honeycomb monolayers, with the polarization angle $\alpha$ controlling the band gap and electronic transport. In the high-frequency regime, we derive an effective Floquet Hamiltonian in which the hopping amplitudes are renormalized by angle-dependent Bessel functions. The response is ${180}^{\circ }$-periodic: generic orientations reduce the point-group symmetry, whereas mirror-aligned angles restore $D_{2h}$ symmetry and pin the extrema of the band gap. Quantum transport calculations for a finite armchair-terminated silicene nanoribbon reveal a polarization-controlled crossover from evanescent to resonant transport. The drive amplitude $\mathrm{\Lambda }$ sets the overall gap scale, while $\alpha$ redistributes spectral weight and mode overlap. These effects together yield three robust current plateaus, each persisting over a wide range of $\mathrm{\Lambda }$ and tolerating $\approx {10}^{\circ }$ variations in $\alpha$. This mechanism applies across honeycomb monolayers, providing design rules for light-controlled multivalued electronics.

Anderson transition, describing the disorder-driven change from extended quantum states to localized ones, plays a fundamental role in understanding wave transport in disordered systems. Here, we realize Anderson transition in a cascaded cavity-magnon system by mapping it to an effective Su-Schrieffer-Heeger model. Within this framework, on-site magnonic disorder is partially transferred—via linear cavity-magnon coupling—to cavity-dominated polaritons, introducing what we term “pseudo-disorder” into the topological chain. Beyond verifying bulk-boundary correspondence in both Hermitian and non-Hermitian regimes, we identify Anderson localization through Poisson-distributed level-spacing statistics. Moreover, under non-Hermitian conditions, we observe that non-Bloch $\mathcal{PT}$-symmetry-like breaking triggers a transition from real-energy to complex-energy localized modes. This work deepens the understanding of disorder-induced localization in non-Hermitian topological systems and reveals the spectral signatures of the Anderson transition beyond the Hermitian paradigm.

We investigate the symmetry-enforced line nodes of the triplet excitations of $X{\mathrm{CuCl}}_3$ ($X=\mathrm{Tl},\mathrm{K}$), showing that they are protected by nonsymmorphic symmetries and are unaffected by microscopic details, such as interaction and anisotropy strength, as long as the ground state and the symmetry group remain unchanged. Extending the conventionally used isotropic spin model for $X{\mathrm{CuCl}}_3$, our analysis includes all the symmetry-allowed anisotropies and gives a detailed account of the role they play in the band topology of triplets. We show that the triplet line nodes carry nontrivial Berry phases and compute their ${\mathcal{Z}}_2$ topological indices. To investigate the effect of breaking the nonsymmorphic symmetry protecting the triplet nodes, we applied a magnetic field tilted away from the high symmetry (010) axis. We find that while the $g$-tensor anisotropy behaves as a trivial mass gapping out the triplets, exchange anisotropies supply a nontrivial momentum-dependent mass term. Analogous to Haldane's original model, the competition of these mass terms determines the nature of the band topology in $X{\mathrm{CuCl}}_3$. To enable an analytic study of the band topology, we derive an effective Dirac Hamiltonian and validate it by computing the band structure and topological indices in the nodal line and gapped phases from the linear bond-wave formalism.

Pure spin current generation in two-dimensional (2D) altermagnets is of considerable interest in spintronics. Here, we develop a general phenomenological formalism for the spin Hall effect driven by the circular bulk photovoltaic effect (BPVE) in 2D semiconducting altermagnets with $C_{4\text{v}}$ and $D_{2\text{d}}$ symmetry. In such altermagnetic systems, the spin splitting in the momentum space is alternated between the $\mathrm{\Gamma }\to X$ and $\mathrm{\Gamma }\to Y$ directions, and the photoresponse tensor of the BPVE, ${\gamma }_{xy}$ and ${\gamma }_{yx}$ are equal in magnitude. This enables the generation of a pure spin current along the transverse direction, while a charge current along the longitudinal direction, thereby inducing the spin Hall effect via the circular BPVE. The spin Hall angle can be calculated from the spin-polarized photoresponse tensors. Specifically, we demonstrate through first-principles calculations and quantum transport simulations that a sizable spin Hall effect can be induced in the 2D altermagnet ${\mathrm{V}}_2\mathrm{SeTeO}$($C_{4\text{v}}$ symmetry), which exhibits a spin Hall angle much larger than 1, indicating high efficiency in pure spin current generation. Our results show the promise of altermagnets for spintronic applications.

We characterize optical transitions of neodymium ions $\left({\mathrm{Nd}}^{3+}\right)$ in antiferromagnetic neodymium gallate $\left({\mathrm{NdGaO}}_3\right)$ with applied fields up to 3 T. The magnetic phase of this material has not previously been studied with the field along its magnetization axis. The measured optical spectra indicate three magnetic phases—antiferromagnetic, intermediate, and saturated—where the intermediate phase likely forms a different magnetic structure from typical spin-flop phases. The observed absorptions were classified into two distinct families of optical transitions: single-Nd and two-Nd absorptions. We demonstrate that the optical transitions in the antiferromagnetic and saturated phases can be modeled using a standard single-ion crystal-field Hamiltonian that interacts with a mean magnetization from the rest of the lattice, and we expand that model to encompass pairs of ions, explaining the origins of the two-Nd transitions. This study offers a deeper understanding of the optical transitions in rare-earth antiferromagnetic crystals, which have been recently attracting significant interest for microwave-to-optical quantum transduction, despite being relatively unexplored to date.

We examine, both experimentally and theoretically, the behavior of an incommensurate magnetic helicoidal structure in a magnetic field applied in the plane in which spins lie. The experimental study is performed on the multiferroic ${\mathrm{NdFe}}_3{\left({\mathrm{BO}}_3\right)}_4$ using bulk magnetic measurements and single-crystal neutron diffraction. We obtain that the wave vector of the helicoidal magnetic structure remains unchanged upon the field increasing until 0.9 T, when the first-order transition to the commensurate spin-flopped antiferromagnetic structure takes place. We propose a theoretical model describing this field evolution. It is shown that the field-induced distortion of the incommensurate magnetic helix can be deduced from the field evolution of the uniform magnetization and intensities of magnetic satellites measured by the single-crystal neutron diffraction.