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.

The two-dimensional homogeneous electron gas (2D HEG) is a prototype system of fundamental interest that can be realized experimentally over a wide range of densities. Here, we investigate its collective charge excitations at low densities, using time-dependent density functional theory. We demonstrate that, beyond traditional plasmons, additional collective excitonic modes emerge for a Wigner-Seitz radius larger than $r_{\mathrm{s}}\approx 1$. These excitonic modes leave characteristic fingerprints in experimentally accessible quantities, namely, asymmetric peak structures in the loss function and very strong Friedel-like oscillations in the static linear density response that increase when the system approaches a regime of instability. Indeed, at low enough densities the collective modes cross the zero energy axis, indicating an instability of the paramagnetic 2D HEG toward the formation of a charge-density-wave phase with excitonic origin. These findings provide valuable insights for the experimental detection of excitonic collective modes in tunable 2D electron systems and contribute to the fundamental understanding of many-body effects in low-density electron gases.

Plastic deformation is widely regarded as an intrinsically dissipative phenomenon whose theoretical description relies heavily on phenomenological constitutive assumptions. We argue instead that defect-mediated plasticity possesses a universal, nondissipative backbone: the kinematics and mobility constraints of defects are fixed by symmetry and conservation laws prior to dissipation. Starting from the spontaneous breaking of spacetime symmetries in a crystalline phase, we construct an effective field theory in which elasticity reorganizes into a coupled higher-rank tensor-vector gauge structure emerging directly from stress and defect conservation laws rather than being postulated microscopically. Dislocations, disclinations, and singular frame-geometric configurations appear as gauge sources whose coupled continuity equations and mobility constraints follow from generalized Gauss laws. The construction provides a symmetry-based organization of the kinematic sectors relevant to defect-mediated plasticity and a starting point for a subsequent dissipative theory of defect motion and stress relaxation.

We report a detailed anisotropic study on the magnetic and transport properties of a ${\mathrm{CeRu}}_2{\mathrm{Ge}}_2$ single crystal. A clear ferromagnetic transition is observed at $T_{\mathrm{C}}=7.5\mathrm{K}$ in the magnetic susceptibility, electrical resistivity, and heat capacity measurements. The magnetoresistance (MR) is positive at low temperature within the magnetically ordered state. We confirmed the presence of a magnon excitation gap in the resistivity, MR, and low temperature heat capacity data. The pronounced anisotropy observed in the magnetic susceptibility and magnetization along the [100] and [001] directions is quantitatively explained within the crystal electric field (CEF) framework using the point-charge model. The analysis reveals a CEF level scheme comprising three doublets, with a ground state and two excited states at 491 and 671 K, that was further confirmed from the Schottky effect in the magnetic part of the heat capacity data. Unlike most Kondo lattice ferromagnets of Ce compounds, where the magnetic easy axis deviates from the expected CEF ground state, ${\mathrm{CeRu}}_2{\mathrm{Ge}}_2$ exhibits magnetization, which is fully consistent with the CEF derived ground state wave function, with the easy axis of magnetization aligned along the [001] direction.

A promising application of machine learning is the creation of low-cost surrogate models to mitigate computational bottlenecks in quantum many-body simulations. Here, we explore whether a neural network (NN) can be trained in the low-data regime, with one to two orders of magnitude fewer training examples than previous works, as an efficient substitute for the impurity solver in dynamical mean-field theory simulations of correlated electron models. We show that the NN solver achieves accuracy comparable to popular continuous-time quantum Monte Carlo (CT-QMC) impurity solvers when interpolating between samples within the training set. While the NN's performance decreases notably when extrapolating to lower temperatures outside the training distribution, its output still provides an excellent initial guess for input to more accurate CT-QMC impurity solvers, thus accelerating the time to solution up to a factor of five. We discuss our results in the context of rapid phase-space exploration.

While numerous models exist which explain certain aspects of irradiation-induced nanopatterning on semiconductors, a comprehensive theoretical explanation has remained elusive. However, it is increasingly apparent that such a model will require understanding the dual influence of the collision cascade initiated by ion implantation: first, as a source of material transport by sputtering and atomic displacements occurring over short timescales, and, second, as a source of defects permitting viscous flow within the thin, amorphous layer that results from sustained irradiation over longer timescales. To better understand the latter, we develop several asymptotic approximations for coupling the local ion flux experienced by the amorphous layer to the layer's evolving free interface. From these and the physical hypothesis of irradiation-induced anisotropic plastic flow, or “ion hammering,” we derive a generalized Kuramoto-Sivashinsky–type equation for the evolving free surface. With physically plausible parameters, the present model achieves good quantitative and qualitative agreement with several aspects of experimental observations of nanopattern formation during irradiation of silicon by argon, krypton, and xenon, and with projectile energies from 500 to 2000 eV. Disagreements between model and experiment are discussed, as are implications for future directions.

We introduce the Zitterbewegung areal rate operator to study the relation between the orientation of trembling motion and band topology. Constructed from the oscillatory interband displacement and velocity, this operator distinguishes clockwise from anticlockwise motion. For a generic gapped two-band Hamiltonian in two dimensions, we show that the Zitterbewegung areal rate is proportional to the Berry curvature. The derivation uses only spectral projectors and is therefore gauge invariant. We also demonstrate that the Zitterbewegung areal rate operator is time independent and a constant of motion at each momentum, although the displacement and velocity from which it is constructed oscillate in time. Its sign distinguishes anticlockwise from clockwise Zitterbewegung and coincides with the sign of the Berry curvature. For wave packets narrowly localized around the isolated massive Dirac points, the Zitterbewegung chirality equals the sign of the local Chern contribution. The Chern number can therefore be reconstructed from the orientations of the Zitterbewegung motion around the individual Dirac points.

Electron–hole plasma in two-dimensional solid-state systems has previously been studied mainly in two limiting cases: the degenerate regime in semimetals with parabolic bands, and the nondegenerate symmetric Dirac regime in graphenelike materials. Here we investigate a third, qualitatively different case realized in a gapless HgTe quantum well: a multicomponent plasma with a hybrid spectrum, in which massless Dirac carriers coexist with thermally activated heavy holes from lateral valence-band valleys. Near the charge-neutrality point we observe a pronounced increase of the resistance with temperature, following an approximately $T^2$ law, in sharp contrast to the nearly temperature-independent resistivity expected for a symmetric two-component Dirac plasma. We show that this behavior originates in the charge-neutrality condition, which, once the heavy holes are populated, pins the chemical potential above the Dirac point: the Dirac electrons remain moderately degenerate, while the heavy holes stay nondegenerate and obey Boltzmann statistics. Because the light degenerate electrons scatter almost elastically off the heavy Boltzmann holes, the interparticle transport admits a relaxation-time description and can be treated nonperturbatively. Using carrier densities from self-consistent band structure calculations, we find that the data are well reproduced by a short-range interaction between Dirac electrons and heavy holes in the weakly disordered limit for which the electronic conductivity scales as $T^{-2}$ and the excess resistivity is proportional to the heavy-hole density, whereas an unscreened Coulomb interaction would leave the conductivity temperature independent. The extracted interaction amplitude is of the Coulomb scale expected at the low charge-neutrality density. Our results establish near-critical HgTe quantum wells as a versatile platform for studying interaction-driven transport in multicomponent systems combining degenerate massless and nondegenerate massive carriers in which the linear Dirac spectrum decouples the current from the total momentum.

Recent numerical and theoretical studies on the two-dimensional $J\text{−}{Q}_3$ model suggest that the deconfined quantum critical point is actually a $\mathrm{SO}\left(5\right)$-symmetry-enhanced first-order phase transition that is spontaneously broken to $\mathrm{O}\left(4\right)$. However, the precise nature of the transition remains under active discussion. Despite extensive studies based on static quantities and entanglement properties, its low-energy excitation spectrum has received comparatively less attention. Here we investigate the dynamical spectra of spin and bond operators at the deconfined critical point of the $J\text{−}{Q}_3$ model using large-scale quantum Monte Carlo simulations and contrast them with the well-established $\mathrm{O}\left(3\right)$ Wilson-Fisher criticality in the $J_1\text{−}{J}_2$ columnar dimerized Heisenberg model. Although both models exhibit two gapless magnon modes in the Néel phase, their critical behaviors diverge strikingly. At the $J_1\text{−}{J}_2$ critical point, the Higgs mode becomes gapless, yielding three gapless modes that reflect the complete restoration of the $\mathrm{O}\left(3\right)$ symmetry. In the $J\text{−}{Q}_3$ model, we instead observe transverse excitations associated with the Néel and VBS order-parameter fluctuations becoming gapless at the transition, a behavior consistent with the emergence of $\mathrm{SO}\left(5\right)$ symmetry. While transverse modes become gapless at the transition, the behavior of the longitudinal (Higgs) mode remains unresolved.