Using auxiliary-field quantum Monte Carlo simulations, we study the zero-temperature attractive Hubbard model on the kagome lattice at various relevant electronic fillings. The low-energy physics at $2/3$-density is influenced by the Dirac point at the Fermi energy, wherein we unveil a superfluid transition at a critical attractive interaction $U_c/t=-4.58\left(3\right)$, which belongs to the chiral-XY universality class. This U(1) symmetry-breaking is not accompanied by charge order, even for substantially large interaction strengths, in a regime where a description in terms of hardcore bosons becomes increasingly suitable. An investigation of the latter shows that charge ordering at $1/3$-filling only occurs at interaction strengths much larger than those corresponding to the mapping to the original fermionic model. Additionally, for densities exhibiting van Hove singularities in the noninteracting density of states, our results show that any attractive interaction gives rise to superfluidity, yet again without charge ordering, contrary to recent studies employing mean-field theory.

Two-dimensional topological insulators (2D TIs) are commonly realized either through intrinsic band-gap inversion within a single material or through interfacial band-offset inversion in narrowly tuned heterostructures. Here we demonstrate, based on first-principles calculations, that these two mechanisms can be unified within a single heteroepitaxial platform. We show that monolayer ${\mathrm{GaAs}}_{1-x}{\mathrm{Bi}}_x$ grown on GaSb(111) hosts a robust 2D TI phase for all alloy compositions $0\le x\le 1$, with a large topological gap ranging from ∼90 to 240 meV. Layer- and orbital-resolved band analyses show a smooth evolution from interfacial band-offset inversion at low Bi concentration to intrinsic band-gap inversion at high Bi concentration. This evolution is captured by a two-band Dirac (Bernevig-Hughes-Zhang  model-type) Hamiltonian with a continuously inverted Dirac mass, placing all band-alignment regimes within the same topological universality class. Our results establish a realistic III–V semiconductor platform for integrating large-gap 2D TIs into wafer-scale device architectures.

We theoretically predict the interaction between polaritonic excitations arising from the coupling of a cavity photon mode with bound to continuum intersubband transitions in a doped quantum well. The resulting exciton bound by photon exchange, recently demonstrated experimentally, exhibits a binding energy that can be continuously tuned by varying the cavity frequency. We show that polariton-polariton interactions, originating from both Coulomb interactions and Pauli blocking, can be dramatically enhanced by reducing the exciton binding energy, thereby increasing the effective Bohr radius along the growth (vertical) direction. This regime is reminiscent of Rydberg atoms, where weak binding leads to strong quantum interactions. Our predictions indicate that this physics can give rise to giant quantum optical nonlinearities in the mid and far infrared, a spectral region that remains largely unexplored in quantum optics and offers exciting opportunities for both fundamental studies and applications.

Quantum-critical many-body states host universal correlations extending across all length scales. Whether these critical correlations merely characterize quantum-critical matter or can actively generate interactions that organize collective order has remained an open question. Here, we establish the concept of quantum-critical mediation, in which a quantum-critical state functions as an active mediator that dynamically generates effective interactions between otherwise weakly coupled degrees of freedom. We demonstrate this mechanism experimentally in a radical-Ni quantum magnet, where strongly coupled spin-1/2 chains realize a Tomonaga-Luttinger liquid (TLL) and anisotropic spin-1 moments remain as low-energy degrees of freedom. Combining thermodynamic measurements, quantum Monte Carlo simulations, bosonization, and conformal field theory, we show that critical TLL correlations generate an emergent two-dimensional interaction network that stabilizes long-range antiferromagnetic order. Our results reveal another function of quantum-critical matter—not merely as a phase exhibiting universal correlations, but as an organizing element that creates interactions and drives collective order. This work establishes quantum-critical mediation as a general organizing principle for emergent collective phenomena and provides a framework for engineering collective states from critical many-body correlations.

Entanglement asymmetry provides a quantitative measure of symmetry breaking in many-body quantum states. Focusing on inhomogeneous $\mathrm{U}\left(1\right)$ charges, such as dipole and multipole moments, we show that the typical asymmetry is bounded by a universal fraction of its maximal value. Multipole charges naturally arise in systems with Hilbert-space fragmentation, where the dynamics splits into exponentially many disconnected sectors. Using the commutant algebra formalism, we generalize entanglement asymmetry to account for fragmentation. While the asymmetry grows logarithmically for conventional symmetries, it can scale extensively in fragmented systems and distinguish classical from quantum fragmentation. We derive general upper bounds for the asymmetry and identify states that saturate them. To study the typical behavior of the asymmetry, we consider the ensemble of random matrix product states. By identifying the bond dimension with an effective time parameter, we qualitatively reproduce recent results on asymmetry dynamics in random quantum circuits, suggesting a universal behavior for the asymmetry of $\mathrm{U}\left(1\right)$ charges in local ergodic systems.

A detailed theoretical understanding and experimental characterization of magnetic nanoelectromechanical devices is crucial for future technological applications. Here, we investigate the transport characteristics of a nanoelectromechanical spin-valve device, which is coupled to two magnetically polarized electrodes with arbitrary polarization directions and strengths. For a weak polarization, the electron transport is dominated by electron shuttling at a low damping. As the polarization increases, the electronic current decreases monotonically, until the system reaches a renormalized tunneling regime. Intriguingly, in between these two limiting regimes, the current noise can exhibit a nonmonotonic turnover as a function of the polarization, and is vastly enhanced due to the competition of the dynamical spin blockade and the bistable mechanical behavior. As the polarization increases, the bistable mechanism is quickly destroyed, resulting in a transition from a local noise maximum into a minimum at the antiparallel magnetization configurations. These findings may shed light on potential ways to achieve polarization-controlled current and noise modulation in nanoelectromechanical spin-valve systems.

We investigate linear exciton transverse transports in monolayer two-dimensional semiconductors within the semiclassical transport framework. By deriving the exciton Berry curvature in momentum space for a general inhomogeneous two-dimensional system, we show that it is determined by both the Berry curvatures and effective masses of the constituent electron and hole. As representative examples, we analyze the exciton Hall and Nernst responses in monolayer transition-metal dichalcogenides (TMDs) and black phosphorus (BP). We find that, in these systems, a linear Berry-curvature-driven exciton Hall or Nernst current is strictly forbidden by symmetry, consistent with previous experimental observations of exciton Hall transport in monolayer ${\mathrm{MoSe}}_2$. In contrast, despite its vanishing exciton Berry curvature, monolayer BP supports a sizable linear transverse exciton current arising from its strong effective-mass anisotropy and the nonequilibrium part of the exciton distribution function in the Boltzmann equation. Our results show that crystalline anisotropy can generate a significant linear exciton transverse response in monolayer semiconductors without relying on Berry-curvature effects. This mechanism provides a distinct route toward controlling exciton transport and may offer useful guidance for future optoelectronic applications and experimental studies of excitonic transverse responses.

We investigate the microwave-power dependence of magnon-photon coupling in a yttrium iron garnet-sphere/split-ring resonator hybrid system at room temperature and demonstrate that nonlinear spin-wave interactions suppress the coupling through power-induced dissipation of magnetostatic modes. At low microwave power, the modes exhibit pronounced level repulsion, evidencing strong coupling to the microwave field. As the power increases, however, magnon-linewidth broadening progressively weakens the coupling and ultimately suppresses it entirely below a threshold external magnetic field. We show that this behavior originates from Suhl's first-order instability: Magnetostatic modes, which couple to the resonator, parametrically excite two counterpropagating magnons at half their frequency, causing modes below the threshold external magnetic field to vanish. In contrast, magnon modes above the threshold field remain robust even at high power, as the instability criterion is not satisfied in that regime. These results reveal a well-defined nonlinear boundary for magnon-photon coupled systems and highlight a favorable regime for exploiting nonlinear magnonics for frequency conversion, switching, and other functional magnonic devices.

The nitrogen-vacancy (NV) center in diamond is the prototype quantum defect that enables a variety of diamond-based quantum technologies. However, charge-state instability and spectral diffusion, often induced by substitutional nitrogen impurities (${\mathrm{N}}_{\mathrm{C}}$), remain key challenges for device performance. Here, we employ first-principles density functional theory calculations to quantitatively investigate nonradiative carrier capture processes mediated by multiphonon emission at both the NV center and the ${\mathrm{N}}_{\mathrm{C}}$ impurity. For relevant cases, we also compute the rates of radiative and thermal emission processes. For ${\mathrm{N}}_{\mathrm{C}}^0\to {\mathrm{N}}_{\mathrm{C}}^{-}$, we obtain an electron capture coefficient of $2.2\times {10}^{-8}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$ at 300 K. Both the magnitude and the temperature dependence are in excellent agreement with experimentally measured capture cross sections. Electron capture at ${\mathrm{N}}_{\mathrm{C}}^{+}$ is even faster, with a capture coefficient of $1.0\times {10}^{-4}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$ at 300 K. For the NV center, we find that carrier capture rates involving only the ground states of ${\mathrm{NV}}^0$ and ${\mathrm{NV}}^{-}$ are negligibly slow. However, capture into the excited states (${\mathrm{NV}}^{0*}$ and ${\mathrm{NV}}^{-*}$) is significantly faster. In particular, the capture coefficient for the hole capture process ${\mathrm{NV}}^{-}\to {\mathrm{NV}}^{0*}$ is as large as $1.8\times {10}^{-7}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$ and largely temperature independent. Hole capture at ${\mathrm{NV}}^{-}$ will thus occur via nonradiative capture into an excited state of ${\mathrm{NV}}^0$ followed by fast radiative decay to the ${\mathrm{NV}}^0$ ground state. Similarly, electron capture at ${\mathrm{NV}}^0$ will occur via the ${\mathrm{NV}}^0\to {\mathrm{NV}}^{-*}\to {\mathrm{NV}}^{-}$ pathway, but with a lower nonradiative capture coefficient ($2.1\times {10}^{-9}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$ at 300 K). Our calculated capture coefficients and rates provide essential information for analyzing charge-state dynamics.

Spin-torque vortex oscillators provide a model system for the nonlinear dynamics of a confined magnetic texture. Their motion is commonly described by the Thiele equation, but its standard form keeps the gyrovector and damping tensor fixed at their rigid-vortex values and becomes inaccurate at large gyration amplitudes. We introduce a data-driven Thiele equation approach that extracts effective, position-dependent Thiele coefficients from a single current-ramp micromagnetic simulation by interpolating the magnetization in vortex-core-position space. The extracted maps reveal a weak increase of the gyrovector magnitude and a pronounced separation of the radial and azimuthal dissipation as the orbit expands, providing quantitative signatures of confinement- and motion-induced vortex deformation. Because the gyrotropic, dissipative, conservative, and spin-transfer contributions retain their usual Thiele structure, the resulting description remains physically interpretable rather than acting as a black-box surrogate. Incorporating these state-dependent coefficients into the equation reproduces the nonlinear stable-orbit dynamics and accurately predicts the response to time-varying currents, whereas a conventional constant-coefficient description predicts vortex expulsion. The framework therefore provides a systematic route for deriving effective collective-coordinate dynamics from full micromagnetic states with high computational efficiency.

Crystal-field symmetry restricts the ground-state Kramers doublet of ${\mathrm{ErBr}}_3$ to one of two classes. We show that the compressed octahedral environment selects the class with $\langle {\psi }_{\pm }\left|J^{\pm }\right|{\psi }_{\mp }\rangle =0$, suppressing the lowest-order $J^{\pm }$-mediated exchange. Thermodynamic measurements reveal two zero-field anomalies at 0.375 and 0.200 K. Under an in-plane magnetic field, the thermodynamic response separates into a phase boundary and a broader crossover line. Inelastic neutron scattering measurements at 2 K reveal no well-defined low-energy dispersive magnetic modes. These results connect the ground-state symmetry with the field-dependent thermodynamic response of ${\mathrm{ErBr}}_3$, providing a microscopic starting point for understanding its low-energy magnetic behavior.

The Ni-Co-V medium-entropy alloy exhibits exceptional strength and ductility, often attributed to its pronounced chemical short-range order (CSRO) driven by Ni-V and Co-V affinity. Yet how this tunable CSRO governs stacking-fault energetics and dislocation motion remains unresolved. Using atomistic simulations based on our first-principles-trained interatomic potential, we show that as CSRO intensifies, the average intrinsic stacking-fault energy increases from 25 to $95\text{mJ}{\text{m}}^{-2}$ and the mean critical resolved shear stress rises from $340.9\pm 23.0$ to $521.3\pm 20.9\text{MPa}$. Dislocation analysis reveals reduced partial separation and enhanced resistance to partial-dislocation glide with increasing order. Introducing Ni-V- and Co-V-rich CSRO clusters along the glide plane induces bowing, kinking, and transient pinning, demonstrating spatially heterogeneous chemical strengthening. These results quantitatively link CSRO to stacking-fault-mediated plasticity and establish tunable strength-ductility through controlled local chemical order in Ni-Co-V systems.

Quantum many-body systems in cavities combine the rich physics of condensed matter systems or quantum chemistry with strong coupling to the surrounding electromagnetic field. In these systems, large Hilbert spaces, many-body interactions, and strong system-environment coupling are all fundamental, posing a significant barrier for established methods in quantum optics and condensed matter physics. Here we propose a novel method based on a combination of the Bogoliubov-Born-Green-Kirkwood-Yvon (BBGKY) hierarchy [M. Bonitz, Quantum Kinetic Theory (Springer International Publishing, Cham, 2016)] and the Hierarchical Equations of Motion (HEOM) [Y. Tanimura, Phys. Rev. A 41, 6676 (1990)] to achieve a rigorous description of open many-body systems in contact with structured photonic and phononic baths. We rationalize that this stacked hierarchy accounts for spin squeezing and superradiant emission despite its applicability to arbitrarily many emitters. The potential of BBGKY-HEOM is then demonstrated for many-body electronic systems embedded in host materials (e.g., molecules in organic crystals). We show that the impact of phononic coupling and charge noise can be as relevant as electronic correlation. Our work establishes an accessible, yet rigorous, route between condensed matter and quantum optics, fostering the growth of a new domain at their interface.

Interfaces in magnetic multilayers play a decisive role in determining their structural and magnetic properties, which significantly impact the performance of the spintronic devices. This work investigates the bottom and top interfaces of a few-nanometer-thick ${}^{57}\mathrm{Fe}$ layer in an $\mathrm{Ag}\text{/}{}^{57}\mathrm{Fe}\text{/}\mathrm{Ag}$ trilayer. The subnanometer depth resolution was obtained using x-ray standing waves (XSWs) generated by an underlying ${\left[\mathrm{W}/\mathrm{Si}\right]}_{10}$ multilayer. Each interface was selectively probed by scanning the standing-wave antinodes across the trilayer by varying the x-ray incidence angle around the Bragg condition. Detailed depth-resolved structural and magnetic information was obtained by combining the x-ray fluorescence (XRF) with isotope-selective (${}^{57}\mathrm{Fe}$) grazing-incidence nuclear resonance scattering (GINRS) under XSW conditions. The results reveal a pronounced asymmetry in the interfacial roughness; the ${}^{57}\mathrm{Fe}$-on-Ag interface exhibits a larger rms roughness of $9.7\pm 1.0 \AA$, whereas the Ag-on-${}^{57}\mathrm{Fe}$ interface is comparatively smoother, with a roughness of $6.4\pm 1.0 \AA$. Correspondingly, GINRS measurements probed distinct hyperfine fields at the two interfaces, consistent with the observed structural asymmetry. Temperature-dependent measurements reveal enhanced interfacial intermixing. Fe $K$-edge extended x-ray absorption fine structure spectroscopy combined with temperature-dependent magnetic measurements shows that annealing at $325{}^{\circ }\mathrm{C}$ induces strong nanoscale intermixing, resulting in the formation of Fe nanoparticles embedded in Ag. These results demonstrate that XSW-assisted XRF and GINRS provide a powerful and interface-specific probe of buried structural and magnetic asymmetries, offering valuable insights for the design and optimization of spintronic multilayer nanostructures.

A fundamental objective of materials modeling is identifying atomic structures that align with experimental observables. Conventional approaches for disordered materials involve sampling from thermodynamic ensembles and hoping for an experimental match. This process is inefficient and offers no guarantee of success. We present a method based on modified molecular dynamics that we call molecular augmented dynamics, which identifies structures that simultaneously match multiple experimental observables and exhibit low energies as described by a machine learning interatomic potential (MLIP) trained from ab initio data. We demonstrate its feasibility by finding representative structures of glassy carbon, nanoporous carbon, ta-C, a-C:D, and $\mathrm{a}\text{−}{\mathrm{CO}}_x$ that match their respective experimental observables—x-ray diffraction, neutron diffraction, pair distribution function and x-ray photoelectron spectroscopy data—using the same initial structure and underlying MLIP. The method is general, accepting any experimental observable whose simulated counterpart can be cast as a function of differentiable atomic descriptors. This method enables a computational microscope into experimental structures.

The Grassmann time-evolving matrix product operator (GTEMPO) method, which represents the Feynman-Vernon influence functional as a temporal matrix product state, has been shown to be a flexible and potentially scalable solution for fermionic quantum impurity problems. In this work, we extend GTEMPO to solve fermionic impurity problems in the Nambu formalism, in which the impurity is coupled to a superconducting bath. A key insight is that by employing the Bogoliubov transformation for the superconducting bath, one could obtain the analytic expression of the Feynman-Vernon influence functional in a similar form to the case of a normal bath, after which the core algorithms of GTEMPO can be straightforwardly adapted. We demonstrate the accuracy of our method by benchmarking it against exact diagonalization in several exactly solvable cases, and against the continuous-time quantum Monte Carlo method using converged dynamical mean-field theory iterations on the imaginary contour in the nonintegrable case. In all cases, we perform both imaginary- and real-time calculations to illustrate the flexibility of our method. These results illustrate that our method, termed Nambu-GTEMPO, could be potentially useful as a quantum impurity solver to study the superconducting states in both equilibrium and nonequilibrium systems.

Extending earlier studies based mainly on configurations or auxiliary-field variables, we apply principal component analysis (PCA), an unsupervised dimensionality-reduction machine-learning method, to dynamical functions of quantum many-body systems obtained from numerically exact continuous-time quantum Monte Carlo simulations. We examine whether PCA can detect phase transitions and crossovers and reveal the underlying dynamical changes in the Hubbard, transverse-field Sherrington-Kirkpatrick (SK) spin glass, and Kondo models. In the Hubbard model, PCA is applied to spectral functions. We find that the leading principal-component (PC1) scores, which measure the projection onto the dominant variation, show an anomaly near the metal-insulator transition. The corresponding loading vector, which gives the weight of each frequency point in the dominant variation, identifies spectral weight transfer from the quasiparticle region around $\omega \approx 0$ to the Hubbard bands. Imaginary-time susceptibility data are used as PCA inputs for both the SK spin glass model and the Kondo model. In the spin glass model, PC1 scores develop a distinct feature at the glass transition as a function of the transverse field for several parameter sets, whereas in the Kondo model they follow universal scaling controlled by the Kondo temperature.

Altermagnets provide a new route to engineer superconducting circuits without magnetic fields. We theoretically study the Andreev bound state (ABS) spectrum of a finite-width altermagnet-based Josephson junction and show how the $d$-wave altermagnetic symmetry and geometric confinement shape its low-energy excitations. We find a clear distinction between the two $d$-wave symmetries: $d_{x^2-y^2}$ order produces spin splitting, whereas $d_{xy}$ order preserves spin degeneracy and exhibits splitting of the ABS spectrum induced by intermode hybridization. Leveraging these novel features, we propose applying a transverse electric field to tune the system and realize a magnetic-field-free, parity-protected superconducting qubit that we call altermon.