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.

The intriguing physics and rich application potential of strongly correlated first-row transition metal oxide compounds result from the complex interplay of several factors that influence the electronic structure. To shed light on the effect of composition, structure, and correlation strength, we apply a well-established charge self-consistent combination of density functional theory and dynamical mean field theory, which has proven to give electron binding energies in good agreement to experimentally derived excitation spectra. For paramagnetic NiO and CoO, we analyze the effect of rock-salt and zinc-blende structures and their different ligand fields on the spectral functions. By varying the value of the interaction parameter $U$, different correlation strengths among the transition-metal $3d$ electrons are considered, as well as the effect of additionally accounting for correlations in the oxygen $2p$ orbitals by a self-interaction-correction pseudopotential scheme. It is shown that this combined DFT+sicDMFT approach leads to spectral functions and band gaps close to experimental data, thereby offering a time-efficient alternative to using a fully correlated model which would treat both metal and oxygen ligand electrons within DFT+DMFT.

Quantum spin liquids (QSLs) are exotic phases of matter characterized by long-range entanglement and the absence of magnetic order even at zero temperature. Here, we present a comprehensive theoretical study of the frustrated magnet ${\mathrm{Y}}_3{\mathrm{Cu}}_2{\mathrm{Sb}}_3{\mathrm{O}}_{14}$ to elucidate its electronic and magnetic properties. We uncover completely opposite crystal-field splittings of the two inequivalent Cu sites owing to their fundamentally distinct oxygen coordination—trigonal distorted octahedral ${\mathrm{CuO}}_6$ and axially compressed ${\mathrm{CuO}}_8$. This inversion places the unpaired hole in the $d_{z^2}$ orbital at the Cu-2 site, while Cu-1 maintains conventional $d_{x^2-y^2}/d_{xy}$ character, which results in a selective band-renormalization of orbitals from the two Cu ions. We further find multiple magnetic instabilities competing with nearly equal strength in this system: the spin susceptibility lacks dominant peaks, and the leading eigenvalues approach unity simultaneously across all wavevectors with increasing interactions. This competitive interplay, originating from the distinct local environments and geometric frustration on the triangular lattice, agrees well with the absence of long-range magnetic order in experiment. Our results support ${\mathrm{Y}}_3{\mathrm{Cu}}_2{\mathrm{Sb}}_3{\mathrm{O}}_{14}$ as a promising QSL candidate where the unique combination of disparate crystal-field environments, strong correlations, and competing exchange interactions conspire to stabilize an exotic quantum ground state.

We present a first-principles study of the electronic structure and thermoelectric properties of Zn-doped SnTe using the Korringa-Kohn-Rostoker method within the coherent potential approximation, complemented by pseudopotential calculations. SnTe is a lead-free analog of PbTe and a candidate thermoelectric material in which Zn doping has been experimentally reported to enhance the performance of $p$-type samples. We show that Zn introduces a resonantlike impurity state, located within the conduction band, which evolves strongly depending on the Zn concentration. This feature leads to a significant enhancement of the thermopower in $n$-type SnTe. In the valence band, Zn doping induces $\mathrm{L}\text{−}\mathrm{\Sigma }$ band convergence, also resulting in an increased $p$-type Seebeck coefficient over a broad concentration range and delaying the onset of the bipolar effect. We further demonstrate that the Zn-induced band-structure modifications drive a transition from an inverted to a trivial band ordering, indicating a controllable topological phase transition. Our results clarify the microscopic role of Zn in SnTe and identify doping as a mechanism for simultaneously tuning thermoelectric and topological properties.

In polar crystals, strong long-range electric fields can distribute defect emission over multiple phonons, obscuring which atomic motions carry the lattice relaxation. AlN's strongly polar lattice and prevalent oxygen-related deep defect centers make it a demanding system for probing how local defect symmetry and electronic transition character select these phonons. Here, we identify axial ${\left(V_{\mathrm{Al}}\text{−}{\mathrm{O}}_{\mathrm{N}}\right)}_{\mathrm{a}}$ as the dominant oxygen-related deep center in AlN by resolving its 815 and $855{\mathrm{cm}}^{-1}$ local vibrational modes (LVMs), and show that its two recombination pathways select different multiphonon relaxation coordinates. The free-to-bound charge-state transition has a large Huang-Rhys factor ($S=9.3$), with an effective phonon energy in the $815{\mathrm{cm}}^{-1}$ LVM region, whereas the intracenter transition ($S=4.9$) lies higher at $877{\mathrm{cm}}^{-1}$, indicating increased contribution from the AlN LO-phonon continuum. More broadly, this AlN case suggests a framework for deep centers in polar wide-band-gap semiconductors, pointing to how defect symmetry and transition character jointly partition lattice relaxation between localized and bulk phonon modes.

Disorder and topology compete in one-dimensional systems, yet analytical results beyond perturbative limits remain scarce. We derive a nonperturbative, energy-dependent expression for the Lyapunov exponent of the disordered Su-Schrieffer-Heeger (SSH) chain in the presence of both on-site and hopping disorder. Our approach is based on a closed recurrence relation for the local density whose disorder average yields an effective transfer problem at the unit-cell level. The resulting energy-dependent Lyapunov exponent quantitatively matches numerical results across a broad range of disorder strengths and hopping asymmetries. We find that the magnitude of the Lyapunov exponent is independent of the topological phase for a semi-infinite chain. We further compute the real-space winding number under disorder and show the contrasting roles of hopping disorder and on-site disorder in the stability of the topological phase.

The layer Hall effect is usually revealed by applying out-of-plane electric fields and electrostatic gating in fully compensated A-type antiferromagnetic layered systems. Here, we theoretically demonstrate that the bilayer system of noncompensated A-type antiferromagnetic ${\mathrm{MnBi}}_2{\mathrm{Te}}_4/{\mathrm{NiBi}}_2{\mathrm{Te}}_4$ heterostructures provides an intrinsic platform to host a spontaneously polarized layer Hall effect. By extending to multilayers, we show that different stacking configurations enable the realization of a nearly quantized layer Hall effect and quantum anomalous Hall effect. These findings make ${\mathrm{MnBi}}_2{\mathrm{Te}}_4/{\mathrm{NiBi}}_2{\mathrm{Te}}_4$ heterostructures a versatile platform for engineering various Hall states in antiferromagnetic van der Waals systems.

Intercalation at the graphene/SiC interface provides a controlled route to stabilize atomically thin layers with properties distinct from their bulk counterparts. In this platform, the structure and stability of the intercalated phase depend sensitively on the defect landscape of the starting substrate. For intercalated two-dimensional silver at the graphene/SiC interface, two phases have been observed: a phase epitaxial to the SiC lattice, called ${\mathrm{Ag}}_{\left(1\right)}$, readily obtained following the conventional intercalation method under ultra-high-vacuum conditions and extensively characterized, and a more densely packed phase, called ${\mathrm{Ag}}_{\left(2\right)}$, which has remained largely unexplored. Here we report an in situ ultra-high-vacuum preparation method of the second phase intercalated at the graphene/SiC interface; this phase was previously prepared via high-pressure confinement heteroepitaxy. Low-energy electron diffraction shows that ${\mathrm{Ag}}_{\left(2\right)}$ is rotated by ${30}^{\circ }$ relative to the SiC lattice and forms supercells, in contrast to the $(1\times 1)$ epitaxial relation of ${\mathrm{Ag}}_{\left(1\right)}$ with SiC. High-resolution angle-resolved photoemission spectroscopy reveals a more complex ${\mathrm{Ag}}_{\left(2\right)}$ band dispersion compared to ${\mathrm{Ag}}_{\left(1\right)}$, as a consequence of the modified Ag-Si interaction in the denser phase. In density functional theory calculations, by defining the unfolding entropy, which, in a quantified way, finds that the band structure of ${\mathrm{Ag}}_{\left(2\right)}$ is more suitable to be unfolded to the SiC primitive cell, the resulting unfolded band dispersion is in great agreement with the experimental data. We further show that the different intercalated Ag phases tune the electronic properties of the overlying quasi-free-standing graphene layer differently: compared with ${\mathrm{Ag}}_{\left(1\right)}, {\mathrm{Ag}}_{\left(2\right)}$ yields an $\sim 1.75$ times higher charge carrier density and modifies the charge-plasmon interaction of the graphene layer, indicating a change in effective screening at the interface.