${\mathrm{SmAgSb}}_2$, a layered magnetic semimetal in the tetragonal $RT{\mathrm{Sb}}_2$ family ($R=\mathrm{Y}$, Sc, rare earth; $T$ = transition metal), is known to exhibit extremely large magnetoresistance (XMR) below its antiferromagnetic (AFM) transition temperature. In this work, we present a comprehensive investigation combining magnetotransport measurements, density functional theory calculations accounting for electron correlation, and angle-resolved photoemission spectroscopy. Our results reveal a complex electronic structure characterized by a multiband Fermi surface and intricate magnetic ground states. We demonstrate that simple two-band models, previously employed in the literature, fail to consistently describe the observed transport phenomena. Notably, we report an XMR of approximately $25200\%$ at 2 K under a 14 T magnetic field, significantly exceeding earlier reports for this material family and rivaling the performance of prominent nonmagnetic XMR systems. This pronounced enhancement below $T_N$ suggests that the XMR originates from a combination of multiband electron-hole compensation and enhanced magnetic scattering in this correlated AFM semimetal.

We study the Kitaev model on regular hyperbolic trivalent tilings. Depending on the length $p$ of the elementary polygons, we examine two distinct tri-colorings of the tiling. Using a recent conjecture on the ground-state flux sector, we compute the phase diagram via exact diagonalizations and derive analytical expressions for the effective Hamiltonians in the isolated-dimer limit which are valid for all values of $p$. Our results interpolate between the Euclidean honeycomb lattice and the trivalent Bethe lattice ($p=\infty$) for which we derive the exact solution of the phase boundaries.

Low-index surfaces of hexagonal (lonsdaleite) silicon and germanium polytypes, 2H-Si and 2H-Ge, are investigated using density functional theory calculations for structural optimization and approximate quasiparticle methods for electronic structure analysis. We examine the relaxed geometries of four surface orientations: ($11\overline{2}0$) $a$ plane, ($1\overline{1}00$) $m$ plane, ($1\overline{1}02$) $r$ plane, and (0001) $c$ plane, encompassing nine distinct terminations. Our calculations reveal a clear energetic hierarchy with surface excess energies increasing in the order: $m$ plane $< a$ plane $< r$ plane $< c$ plane. Surface atomic relaxations are driven by the tendency to eliminate dangling bonds through either pairing or complete filling/emptying with electrons, effectively rendering the surfaces insulating. This behavior is evidenced by the formation of energy gaps between surface-bound states within the fundamental band gap region when projected onto the bulk band structure. We apply approximate quasiparticle methods such as the hybrid functional HSE06 and the shell-LDA-1/2 approach for an accurate description of the band structures. We calculate surface-dependent ionization potentials and electron affinities, and compare our findings with previous results for diamond-structure Si and Ge crystals. These results provide fundamental insights into the surface physics of hexagonal group-IV semiconductors and their potential applications in nanoelectronics.

We study multilayer topological insulators with random interlayer tunneling, known as off-diagonal disorder. Within the Burkov-Balents model a single Hermitian defect creates a bound state whose energy crosses the middle of the gap in the trivial phase but never in the topological phase; a non-Hermitian defect splits this level yet preserves the same crossing rule, so the effect serves as a local marker of topology. Importantly, the key distinction persists: The bound state crosses zero in the trivial phase but not in the topological phase. Two complementary diagrammatic approaches give matching densities of states for the normal, topological, Weyl, and quantum anomalous Hall regimes. Off diagonal disorder inserts bulk states into the gap and can close it: The Weyl phase remains robust under strong disorder, whereas the quantum anomalous Hall phase survives only for weak fluctuations, and the added bulk states shrink the Hall plateau, clarifying experimental deviations. Finally, we analyze edge modes. Uniform disorder shortens their localization length slightly, while Gaussian and Lorentzian disorder enlarge it and in the Gaussian case can even delocalize the edges. Although chirality is maintained, the enhanced overlap permits tunneling between opposite edges and pulls the longitudinal conductance away from its quantized value.

Uranium compounds have long been of significant interest in condensed matter physics due to their diverse and often exotic properties, including heavy-fermion behavior, non-Fermi-liquid characteristics, quantum criticality, and unconventional superconductivity. These phenomena arise from the complex interplay between crystal structure, hybridization of localized $5f$ electrons with conduction electrons, and electron-electron correlations. Here, we present a comprehensive study of the electronic structure of ${\mathrm{UFeGa}}_5$, a layered uranium intermetallic compound, using high-resolution angle-resolved photoemission spectroscopy (ARPES) and density functional theory (DFT) calculations. Three-dimensional electronic structure of ${\mathrm{UFeGa}}_5$ was systematically studied and fine structures of the $\mathrm{U}5f$ bands near the Fermi energy were clearly resolved. Our results reveal that ${\mathrm{UFeGa}}_5$ exhibits a predominantly itinerant nature of $5f$ electrons, with strong band dispersion and significant contributions to the Fermi surface. Theoretical calculations assuming itinerant $5f$ electrons are in excellent agreement with the experimental ARPES data, confirming the weak electron correlation effects in this compound. Temperature-dependent ARPES measurements further demonstrate that the $f$ electrons retain itinerant across the studied temperature range (7.5 to 100 K).

Holes are injected from electrodes or produced by irradiation in many applications of crystalline and amorphous ${\mathrm{Ga}}_2{\mathrm{O}}_3$. They are known to trap in polaron states in both phases. We investigate, using density functional theory, how hole trapping in ${\mathrm{Ga}}_2{\mathrm{O}}_3$ can lead to creation of Frenkel pairs (FPs) of oxygen vacancies in the $+2$ charge state, ${\mathrm{V}}_O^{2+}$, and interstitial oxygen atoms. The calculations reveal that hole bipolarons lead to the formation of O–O dimers, distorting adjacent Ga–O bonds and resulting in a significant reduction of the barriers for the nearest-neighbor FP formation with respect to pristine structures. In amorphous ${\mathrm{Ga}}_2{\mathrm{O}}_3$ the barriers are on average 2.05 eV, much lower than in the crystalline phase, where they are 3.47 to 4.80 eV. Furthermore, in the amorphous phase, the migration barriers for oxygen vacancies in the $+2$ charge state, ${\mathrm{V}}_O^{2+}$, are reduced compared to those in the crystalline phase, indicating that ${\mathrm{V}}_O^{2+}$ can drift away under the influence of electric fields, creating stable defects. These results show that hole trapping in ${\mathrm{Ga}}_2{\mathrm{O}}_3$ can facilitate the formation of FPs, particularly in amorphous structures. They can be useful in understanding the mechanisms of degradation in ${\mathrm{Ga}}_2{\mathrm{O}}_3$ based devices under negative bias and illumination stress.

We employ a multiple scattering expansion to systematically derive curvature corrections to the Casimir-Polder (CP) interaction between small anisotropic particles and general magnetodielectric surfaces. Our results, validated against exact solutions, reveal a complex, distance-dependent interplay between material properties and surface curvature in determining stable particle orientations. We demonstrate that even small surface curvature can induce or eliminate switches in the preferred orientation, a quantum effect that is diminished by thermal fluctuations. This work provides a crucial understanding of how to engineer nanoparticle orientation through tuneable parameters, offering significant implications for micro- and nanomechanical device design.

We investigate the dynamic shear viscosity of the undoped, ABC-stacked multilayer graphene, whose low-energy behavior is captured by a chiral-$N$ effective Hamiltonian with $N$ equal to the number of layers. Electron-electron interactions are analyzed using Feynman diagrams and the random phase approximation (RPA). Evaluating the three leading-order diagrams (self-energy, vertex, and “honey” diagrams), we find that the electron-electron interaction can remarkably enhance the shear viscosity at the low dynamic frequency, where states near charge neutrality dominate the response. In the absence of screening, the interaction-induced contribution diverges in the zero-frequency limit for large layer numbers; this infrared divergence is removed by RPA screening of the Coulomb potential. The resulting viscosity exhibits a nonmonotonic frequency dependence, increasing at low frequency and decreasing at high frequency. Furthermore, in the high frequency regime, where the response is governed by the noninteracting contribution, the viscosity scales linearly with the layer number $N$. Our results demonstrate that electron viscous effects in multilayer graphene can be tuned by frequency and layer number.

We investigate the dynamics of subsystem particle number fluctuations in a long-range system with power-law decaying hopping strength characterized by exponent $\mu$ and subjected to a local dephasing at every site. We introduce an efficient bond length representation for the four-point correlator, enabling the large-scale simulation of the dynamics of particle number fluctuations for both fermionic and bosonic systems and for translationally invariant initial states. Our results show that the particle number fluctuation dynamics exhibit one-parameter Family-Vicsek scaling, with superdiffusive scaling exponents for $\mu <1.5$ and diffusive scaling exponents for $\mu \ge 1.5$. Finally, exploiting the bond-length representation, we provide an exact analytical expression for the particle number fluctuations and their scaling exponents in the short-range limit ($\mu \to \infty )$.

Modeling spin-wave (magnon) dynamics in novel materials is important to advance spintronics and spin-based quantum technologies. The interactions between magnons and lattice vibrations (phonons) limit the length scale for magnon transport. However, quantifying these interactions remains challenging. Here, we show many-body calculations of magnon-phonon (mag-ph) coupling based on the ab initio Bethe-Salpeter equation. We derive expressions for mag-ph coupling matrices and compute them in two-dimensional ferromagnets, focusing on hydrogenated graphene and monolayer ${\mathrm{CrI}}_3$. Our analysis shows that electron-phonon $\left(e\text{−}\mathrm{ph}\right)$ and mag-ph interactions differ significantly, where modes with weak $e\text{−}\mathrm{ph}$ coupling can exhibit strong mag-ph coupling (and vice versa), and reveals which phonon modes couple more strongly with magnons. In both materials studied here, the inelastic magnon relaxation times decrease abruptly above the threshold for emission of strongly coupled phonons, revealing a low-energy window where magnons are long lived. Averaging over this window, we compute the temperature-dependent magnon mean free path, a key figure of merit for spintronics, entirely from first principles. The theory and computational tools shown in this Letter enable studies of magnon interactions, scattering, and dynamics in generic materials, advancing the design of magnetic systems and magnon- and spin-based devices.

We explore novel topological responses and axionlike phenomena in three-dimensional insulating systems with spacetime-dependent mass terms encoding domain walls. Via a dimensional-reduction approach, we derive an axion-electromagnetic coupling term involving three axion fields. This term yields a topological current in the bulk and, under specific conditions of the axions, real-space topological defects such as magneticlike monopoles and hopfions. Moreover, once one of the axions acquires a constant value, a nontrivial boundary theory realizes a $(2+1)$-dimensional analog of the Witten effect, which shows that pointlike vortices on the gapped boundary of the system acquire half-integer electric charge. Our findings reveal rich topological structures emerging from multiaxion theories, suggesting new avenues in the study of topological phases and defects.

We report a localization phenomenon that emerges in non-Hermitian and quasiperiodic coupled systems, which we dub “Anderson-skin (AS) dualism”. The emergence of AS dualism is due to the fact that non-Hermitian topological systems provide nontrivial topology for disordered systems, causing the originally localized Anderson modes to transform into skin modes, i.e., the localized states within the point gap regions have dual characteristics of localization under periodic boundary condition and skin effects under open boundary conditions. As an example, we analytically prove the one-dimensional AS dualism through the transfer matrix method. Moreover, by discussing many-body interacting systems, we confirm that AS dualism is universal.

Recent discoveries of zero-field fractional Chern insulators in moiré materials have attracted intensive research interest. However, most current theoretical and experimental attempts focus on Chern bands with Chern number $\left|C\right|=1$, in analogy to the Landau levels. Here, we propose candidate material systems for realizing fractional Chern insulators with higher Chern numbers. The material setup involves $\mathrm{\Gamma }$-valley twisted homobilayer transition metal dichalcogenides in proximity to a magnetic skyrmion lattice. The skyrmion exchange potential induces a flat band with a high Chern number $C=-2$. Using the momentum-space projected exact diagonalization method, we perform a comprehensive study at various filling factors, confirming the generalized Jain sequence. Our research provides theoretical guidance on realizing unconventional fractional Chern insulators beyond the Landau level picture.

We systematically investigated the correlation between defect formation energy and local stress states in amorphous ${\mathrm{SiO}}_2$ (a-${\mathrm{SiO}}_2$) using first-principles calculations within density functional theory. Although conventional approaches require the structural relaxation of oxygen vacancy at each site, we demonstrated that the formation tendency of oxygen vacancies can be quantitatively predicted from the local stress state in a nondefective system. To achieve this, we employed a real-space analysis based on Bader partitioning and introduced a unit-based averaging method for local structural units, enabling physically meaningful stress evaluations in ionically disordered systems. A strong statistical correlation was found between the formation energy and the unit-averaged stress in the Si–O–Si unit, suggesting that the local compressive environments significantly facilitated oxygen removal with large structural relaxation. These results establish a predictive framework for identifying defect-prone sites in disordered systems, including amorphous structures, without exhaustive defect structure generation, thereby offering an efficient route for defect analysis and material design.

Light-field-driven currents sensitive to pulse waveforms have established a promising foundation for the realization of petahertz (PHz) electronic devices. However, the influence of many-body interactions on photocurrent generation remains inadequately understood. Here, we theoretically investigate photocurrent generation in monolayer $\mathrm{Mo}{\mathrm{S}}_2$, highlighting the essential role of many-body effect on carrier dynamics and the optoelectronic response. We demonstrate that photocurrents depend critically on the electric-field waveform controlled by the carrier-envelope phase, and we reveal a distinct signature of multielectron interactions manifested as destructive interference of the maximum current with increasing field strength, due to specific intraband Coulomb scattering processes that can induce a primary band energy renormalization. Additionally, we propose an optical switch based on two orthogonally linearly polarized laser pulses with a controlled delay, capable of achieving current modulation at frequencies approaching 1 PHz. We present a strategy for constructing logic gates and emphasize the critical role of many-body interactions in the implementation of their functionality encoding. This optical switch also provides an all-electronic method to measure dephasing time on femtosecond timescales. Our findings deepen the understanding of many-body effects in petahertz electronics and facilitate the development of ultrafast optoelectronic devices based on two-dimensional materials.

We present a comprehensive transport study of interface superconductivity in ${\mathrm{La}}_2{\mathrm{CuO}}_4/{\mathrm{LaSrCuO}}_4$ [LCO/LSCO(1.0)] bilayers, where both constituent layers are insulating in bulk. Our experiments reveal that superconductivity is localized within the LCO layer, with holes exhibiting a decaying distribution that extends up to 5 unit cells, reaching optimal superconductivity at the third ${\mathrm{CuO}}_2$ plane. Furthermore, Hall effect measurements indicate a mobile electron layer in LSCO(1.0), suggesting a unique coexistence of electrons and holes at the interface. Superconductivity persists in bilayers with total thickness as thin as 1.5 unit cells. These results provide insights into charge-carrier dynamics at cuprate interfaces and demonstrate robust interfacial superconductivity down to the ultrathin limit.

The recent discovery of heavy-fermion superconductor ${\mathrm{UTe}}_2$ has broadened the possibility of realizing exotic time-reversal-symmetry breaking superconductivity. However, a comprehensive understanding of the topological phases in the superconducting states of ${\mathrm{UTe}}_2$ is still lacking. Here, we present an exhaustive classification of topological phases for all time-reversal-symmetry breaking pairing symmetries of ${\mathrm{UTe}}_2$. Using the K-theoretical classification approach, we uncover that 25 of 36 possible pairing states are classified as higher-order topological phases, with some demonstrating hybrid-order topology through an intricate interplay of hinge and corner states. Furthermore, under the weak-coupling condition of the pair potentials, the possible pairing symmetries are constrained to $B_{ju}+i{B}_{ku}, A_u+i{B}_{ju}$, and $B_{jg}+i{A}_u$ ($j,k=1,2,3$; $j\ne k$), where these symbols denote the irreducible representations of the point group $D_{2h}$. For these pairing states, the topological invariants are related to the Fermi surface topology via the Fermi-surface formula, enabling us to systematically diagnose higher-order topological phases. Using a tight-binding model, we demonstrate the higher-order topological phases of the mixed-parity $A_u+i{B}_{1g}$ and nonunitary-odd-parity $A_u+i{B}_{1u}$ superconductors, where the second-order and hybrid-order topological phases emerge as the number of Fermi surfaces enclosing the time-reversal invariant momentum evolves from two to four. The findings suggest that ${\mathrm{UTe}}_2$ serves as a compelling platform for exploring higher-order topological superconductors with diverse topological surface states.

Emission and absorption of energy are fundamental aspects of nonequilibrium dynamics. The heating induced by driving a many-body system is perhaps the most straightforward diagnostic of the process of equilibration, or the lack thereof. Gapless systems are particularly susceptible to drive-induced heating, and the capacity to control such heating is of experimental importance. Our study addresses this challenge in the framework of conformal field theory (CFT), for which we study families of structured drives up to the aperiodic Thue-Morse sequence. Concretely, we consider a class of spatially inhomogeneous Hamiltonians, where the operator evolution is governed by a nonlinear classical dynamical system $\mathcal{K}$. The existence of invariant regions and fixed points of $\mathcal{K}$ leads to different levels of ergodicity breaking. Upon bridging the gap between this dynamical system and the driven CFT, we classify various dynamical phases of matter, including the heating and nonheating phases, as well as a prethermal phase with a controllably slow heating rate. We further generalize the discussion to $\eta$-random multipolar driving, characterized by $\eta \mathrm{th}$-order multipolar correlation in time. A “triply tunable” parametric dependence of the prethermal lifetime arises as $K^{-2(\eta -\xi )}$, where $K$ quantifies the deviation from the preimages of the fixed points of $\mathcal{K}$, the multipolar order $\eta$, and the order of the preimages $\xi$. Upon sacrificing Hermiticity by considering SU(2) deformed CFTs, we find another nonheating phase with a nonzero measure, inaccessible via purely unitary CFTs. This is underpinned by an emergent compact subspace in the generic $\mathrm{SL}(2,\mathbb{C})$ group structure, which we also identify in the transfer matrix in non-Hermitian systems with binary disorder.

Optical probes have emerged as versatile tools for detecting exotic fractionalized phases in quantum materials. We calculate the low-energy Raman response arising from mobile, interacting Ising anyons in the chiral Kitaev spin liquid perturbed by symmetry allowed interactions—a phase relevant to $\alpha -{\mathrm{RuCl}}_3$ under a magnetic field. At zero temperature, the two-anyon continuum response shows a leading power-law scaling of the intensity near the onset of the signal: $I\left(\omega \right)\sim {(\omega -E_{2\sigma }^0)}^{\frac{1}{8}}$ for linear and parallel-circular polarization channels, where $E_{2\sigma }^0$ is the two-particle gap. Strong corrections due to short-range interactions arise at order $1/4$. For cross-circularly polarized channels, the scaling is given by $I\left(\omega \right)\sim {(\omega -E_{2\sigma }^0)}^{|l\pm 1/8|}$, where the value of $l=0,1,2$ is determined by the number of minima in the single anyon dispersion. The exponents are directly related to the topological spin of Ising anyons ${\theta }_{\sigma }=\pi /8$, describing their exchange statistics. Our theory generalizes to spectral probes of anyonic quasiparticles with multiple band minima in other quantum liquids. Interaction between anyons may also induce bound states, resulting in sharp peaks that show strong polarization dependence.