The crystallographic structure of iron under extreme conditions is a key benchmark for state-of-the-art experimental and computational methods. Moreover, it plays a crucial role in our understanding of planetary cores, as it strongly influences the interpretation of observational data and, consequently, our knowledge of their internal structure and dynamics. However, even the crystal structure of pure solid iron under Earth's core conditions remains uncertain, with the commonly expected hexagonal close-packed phase being energetically competitive with several cubic structures. In this study, iron was compressed in a diamond anvil cell to pressures exceeding 200 GPa and dynamically probed near its melting point using MHz-frequency x-ray pulses from the European X-ray Free-Electron Laser. In the pressure range between 120 and 160 GPa, the high temporal resolution of the structural snapshots at elevated temperatures revealed the face-centered cubic phase, extending its observed stability to higher pressures than previously reported. Brief appearances of intermediate or disordered phases, including body-centered cubic (bcc) and stacking-faulted structures, were also observed. Above 230 GPa, new diffraction reflections emerged at high temperatures and are interpreted as evidence for the nucleation of a previously unreported phase, which subsequently evolved into a powderlike diffraction pattern characteristic of the bcc structure. The unprecedented time resolution of the structural data acquired during rapid heating and cooling cycles provides insights into the kinetics and mechanisms of phase transformations in iron at these extreme pressures.

Quantum-electrodynamical density-functional theory (QEDFT) provides a first-principles framework for describing materials coupled to quantized electromagnetic fields. While QEDFT has successfully captured cavity-induced modifications of electronic structures in atoms and molecules, a fully self-consistent and accurate framework to simulate and predict the structural, phonon-related, polarization, and optical response of periodic solids in optical cavities has remained elusive. Here, we introduce a unified QEDFT approach that combines collective light-matter coupling parameter in the electronic ground state, density-functional perturbation theory for phonons, and real-time time-dependent QEDFT for optical excitations. This framework enables ab initio calculations of cavity-modified electronic and phononic dispersions, Born effective charges, dielectric tensors, and both resonant and nonresonant optical absorption spectra. Using wurtzite gallium nitride (GaN) in an optical cavity as a case study, we demonstrate that the quantized vacuum field reshapes electronic, phononic, and polarization properties, producing experimentally accessible signatures in the dielectric function and absorption spectra. These results establish QEDFT as a general first-principles platform for predicting and exploring cavity-modified quantum materials.

We introduce a mechanism that produces a Hall-like transverse response in time-reversal-invariant materials, driven entirely by geometric effects. Specifically, we demonstrate that a tilted potential interface causes electron wave packets to undergo a refractionlike deflection upon transmission through the barrier, leading to a finite transverse current and a corresponding Hall-like conductance. Our analytical framework captures the essential features of this refraction-driven charge transport, and the resulting transverse conductance profile is corroborated by numerical simulations across different lattice models and device geometries. We further visualize our predicted effect through real-time wave packet dynamics, which reveals its purely geometric origin and the robustness of the transverse response. These findings establish a fundamentally distinct class of Hall-like transport phenomena in mesoscopic systems that preserve time-reversal symmetry.

One-dimensional (1D) moiré superlattices provide a route to engineering reduced-dimensional electronic states in van der Waals materials, yet their electronic structure and microscopic origin remain largely unexplored. Here, we investigate the structural relaxation and electronic properties of a 1D moiré superlattice formed in twisted bilayer $1{\mathrm{T}}^{\prime }\text{−}{\mathrm{WTe}}_2$ using density functional theory calculations, complemented by high-angle annular dark-field scanning transmission electron microscopy. We show that lattice relaxation strongly reconstructs the moiré stripes, leading to stacking-dependent stripe widths that are in excellent agreement with experimental observations. The relaxed structure hosts quasi-one-dimensional electronic bands near the Fermi level, characterized by strong dispersion along the stripe direction and nearly flat dispersion in the perpendicular direction. By comparing the full bilayer with isolated relaxed layers, we establish that these 1D electronic states are governed predominantly by an intralayer moiré potential induced by in-plane lattice relaxation, rather than by interlayer hybridization. We extract this position-dependent moiré potential directly from DFT calculations and construct an effective tight-binding model that reproduces both the band dispersion and the real-space localization of the electronic wave functions. Our results identify lattice relaxation as the key mechanism underlying 1D electronic states in 1D moiré superlattices. The framework developed here provides a unified theoretical basis for realizing and exploring one-dimensional moiré physics in a broad class of anisotropic two-dimensional materials.

Electron-phonon coupling has been a central topic in condensed matter physics for decades, and first-principles methods have demonstrated remarkable success in quantitatively capturing its role in a wide variety of physical phenomena and materials. Conventional calculations of electron-phonon coupling typically assume that phonons have infinite lifetimes, but phonons can exhibit finite lifetimes due to anharmonic phonon-phonon interactions. In this work, we derive an expression for the electron-phonon coupling scattering rates including the effects of anharmonic three-phonon interactions, which lead to phonon dephasing and finite phonon lifetimes. We also describe a first-principles implementation of this anharmonic electron-phonon coupling which can be seamlessly integrated within existing workflows for the evaluation of electron-phonon and phonon-phonon coupling interactions. Finally, we present calculations of electron-phonon scattering rates including phonon dephasing in a range of materials, and discuss the different microscopic mechanisms by which anharmonic phonons influence electron-phonon coupling. This study establishes the importance of finite phonon lifetimes in the evaluation of electron-phonon coupling, and provides a platform to explore these effects in a wide range of materials and phenomena.

We revisit the electronic structure and band topology of monolayer ${1\mathrm{H}-\mathrm{NbSe}}_2$ and its related compounds ${1\mathrm{H}-\mathrm{MoS}}_2$, ${\mathrm{NbS}}_2$, ${\mathrm{TaS}}_2$, ${\mathrm{TaSe}}_2$, and ${\mathrm{WS}}_2$. We construct a six-band, a three-band, and—simplest of all—a single-band model for this material family, by directly Wannierizing the ab initio bands. All hosts obstructed atomic isolated bands away from the atomic positions near the Fermi energy. We find that in the three-band model, the obstructed atomic Wannier function can be well approximated by an optimally compact Wannier function with more than 90% accuracy for all the compounds, rising to a remarkable 94% accuracy in ${\mathrm{NbSe}}_2$. Interestingly, the simplest single-band model has next-nearest-neighbor hopping larger than the nearest-neighbor hopping (by nearly an order of magnitude for ${\mathrm{MoS}}_2$, ${\mathrm{NbSe}}_2$, ${\mathrm{TaSe}}_2$, and ${\mathrm{WS}}_2$), which comes from the cancellation between the atomic on-site terms and the atomic nearest-neighbor hopping after projecting to the obstructed atomic Wannier functions in the underlying three-band model. Furthermore, for ${\mathrm{NbSe}}_2$, we employ a novel approximation scheme to obtain an effective Hamiltonian that captures the three bands originating mainly from the Nb atom. We also use conventional perturbation theory to derive the ab initio obstructed Wannier function with 95% accuracy. Our results pave the way for future study of the effect of quantum geometry on the correlated phases in this family of materials.

The electron-phonon interaction underpins many material properties, for example, the conductivity of metals and the optoelectronic response of semiconductors. First-principles calculations of the electron-phonon interaction are a powerful tool to quantitatively describe many of these properties in increasingly complex materials. However, one key assumption of all calculations is that phonons have infinite lifetimes, an approximation that may break down when anharmonic phonon-phonon interactions are strong. In this work, we present a theory for the interaction of electrons with finite-lifetime phonons experiencing dephasing. Using a first-principles implementation of the theory, we find that anharmonic dephasing dramatically enhances electron-phonon scattering rates in metallic ${\mathrm{MgB}}_2$. Microscopically, phonon-phonon interactions create new scattering channels that increase the phase space available for electron-phonon scattering. As a result, anharmonic dephasing strongly suppresses conductivity in ${\mathrm{MgB}}_2$, bringing the calculated values substantially closer to experiment within the Boltzmann transport equation framework. This example establishes the importance of finite phonon lifetimes in the evaluation of electron-phonon scattering, and the microscopic mechanism suggests that anharmonic dephasing could play an important role in the conductivity of many metals. More broadly, our theory and first-principles implementation of anharmonic dephasing in the electron-phonon interaction provides a solid foundation to explore this regime in other materials.

$\alpha \text{−}{\mathrm{UTe}}_3$, a van der Waals (vdW) actinide compound with a monoclinic ${\mathrm{ZrSe}}_3$-type structure, is a narrow-gap semiconductor with $5f$ moments. ${}^{125}\mathrm{Te}$ NMR reveals strongly anisotropic, layer-confined spin fluctuations below $\sim 20\mathrm{K}$, with the $a$-axis component enhanced, and a signal wipeout at the antiferromagnetic (AFM) transition $T_{\mathrm{N}}=5\mathrm{K}$. Single-crystal neutron diffraction finds $\mathit{q}\approx (0.17,0.5,0)$ and a longitudinal sinusoidal modulation of $a$-axis moments (amplitude $\approx 0.8{\mu }_{\mathrm{B}}$) with AFM stacking along $b$. A crystal electric field singlet-singlet induced-moment framework accounts for the easy-axis anisotropy, the small heat-capacity anomaly at $T_{\mathrm{N}}$, the reduced ordered moment, and the exchange-driven selection of $\mathit{q}$ in this localized $5f$ vdW magnet, establishing a constrained exchange geometry stabilizing this in-plane incommensurate state.

Low-energy magnetic excitations are investigated in ${\mathrm{SeCuO}}_3$ using temperature-, field-, and angle-dependent Raman scattering. We observe the coexistence of a sharp magnon mode and a broad spinon continuum, reflecting the interplay between long-range magnetic order and low-dimensional quantum fluctuations. Upon cooling, spectral weight is progressively transferred from the continuum to the magnon mode. In addition, both excitations exhibit an identical angular dependence governed by the same Raman scattering symmetry, indicating a common coupling to the underlying exchange geometry. Under an applied magnetic field, deviations from fourfold symmetry in the crossed polarization channel reveal the emergence of anisotropic spin correlations. These results suggest that coherent magnons develop from fractionalized spinon excitations in a low-dimensional quantum magnet.

Antiferromagnets with broken time-reversal symmetry (TRS) have launched a new direction in spintronics research, combining the advantageous dynamical properties of conventional antiferromagnets with the controllability typically associated with ferromagnets. However, antiferromagnetic domains are notoriously challenging to image in real space. X-ray magnetic circular dichroism (XMCD) offers a route to overcome this difficulty: XMCD contrast may be finite in TRS-breaking antiferromagnets with an appropriate magnetic space group. Here, we exploit this to image the cluster octupole domains in a focused ion beam-fabricated device of the noncollinear antiferromagnet ${\mathrm{Mn}}_3\mathrm{Sn}$. Using scanning transmission x-ray microscopy, we spatially resolve the weak preedge XMCD contrast (of 0.2%), achieving a contrast resolution better than 0.02%. We observe hysteretic switching of the ferroic cluster octupole order through both the XMCD contrast and the corresponding anomalous Hall effect within the same device. These results confirm the bulk nature of this contrast and establish XMCD-based microscopy as a powerful real-space imaging method for TRS-breaking antiferromagnets, including altermagnets, enabling future studies of their dynamics, switching, and symmetry-tunable phenomena.

Altermagnetism, characterized by its ferromagnetism-like spin-splitting band structure and antiferromagnetism-like magnetic order, has garnered considerable attention recently. Although hole doping may promote magnetism in the debated altermagnet (AM) candidate ${\mathrm{RuO}}_2$, the evolution of its electronic and magnetic properties under hole doping remains poorly understood. Based on first-principles calculations, we employ quantum oscillations to study hole-doped ${\mathrm{RuO}}_2$. We find that hole doping can enhance spin splitting and reconstruct the Fermi surface in ${\mathrm{RuO}}_2$, which is revealed by the angle-dependent quantum oscillation frequency. By tracking a pair of closed Fermi-surface pockets, we identify a meaningful correlation between the magnetic moment of Ru and a quantum-oscillation-based signature of spin splitting. This correlation follows a quasilinear trend over a broad doping range, which can be captured by a minimal two-dimensional $d$-wave AM model. In addition, the hole-doped ${\mathrm{RuO}}_2$ exhibits a transition from a nonmagnetic to an AM state via an intermediate state. The quasilinear correlation through quantum oscillation and the distinct quantum oscillation frequency of the stable AM state can serve as useful signatures for identifying the AM state in ${\mathrm{RuO}}_2$. Our results provide a comprehensive framework for understanding hole-doped ${\mathrm{RuO}}_2$, offering insights into AM transitions and their identification.

We report bright electroluminescence from ambipolar gate-defined lateral $p\text{–}n$ junctions and field effect transistors in dopant-free GaAs/AlGaAs single heterojunctions. A combination of transition energies, lifetimes, and spatial emission profiles as a function of gate voltage, forward bias, temperature, and RF excitation points to free excitons with a predominantly two-dimensional (2D) character, despite the lack of a bottom barrier providing physical confinement. Comparisons with time-resolved photoluminescence further support our findings. We develop an analytical model to explain our results based on the partial screening of electric fields within our devices. Collectively, our results show electrically generated and controllable 2D free excitons, bridging 2D exciton physics and ambipolar gate-defined two-dimensional electron gas/two-dimensional hole gas platforms.

The nature of the superconducting state in two-dimensional transition-metal dichalcogenides remains under active debate. A widely used description invokes so-called Ising superconductivity. In this work, we investigate theoretically this pairing state by employing single magnetic impurities as local probes of the superconducting condensate. We analyze the formation of Yu-Shiba-Rusinov bound states in the presence of Ising spin-orbit coupling and an in-plane magnetic field to study how their spectral properties encode the underlying pairing structure. We identify distinct features in the bound-state spectrum and tunneling response that differentiate this system from conventional superconductors. Our results demonstrate that magnetic impurities provide a sensitive probe of the structure of the superconducting state and yield experimentally accessible signatures of unconventional aspects of Ising superconductivity.

Revealing the mechanisms of phonon scattering is crucial for understanding material properties such as transport characteristics and optical responses. It can be discussed by measuring the temperature dependence of the phonon energy and lifetime. To gain insight into these mechanisms in the Weyl semimetal $T_d\text{−}{\mathrm{WTe}}_2$, we investigated coherent phonons using time-resolved pump-probe spectroscopy in a wide temperature range from 4.6 to 300 K. The temperature dependence of the frequency and decay rate of the two high-frequency optical modes was described by the conventional anharmonic phonon-phonon scattering model. In contrast, the low-frequency mode at 2.4 THz exhibited anomalous behavior, which can be interpreted as the contribution of phonon-electron scattering.

Higher-order topological phases enrich topological classifications by enabling boundary states in multiple dimensions. Despite progress in phononic realizations of type-I higher-order semimetals, type-II phases remain experimentally elusive due to complicated interlayer couplings. Here, we propose a simple and universal mechanism to induce higher-order topological phase transitions from type-I to type-II semimetals via tunable interlayer coupling in a tight-binding model. Guided by this framework, we realize a type-II higher-order Weyl acoustic scatterer structure with $C_2$ symmetry that simultaneously supports two-dimensional Fermi arc surface states and one-dimensional hinge states. The acoustic architecture faithfully reproduces the tight-binding band dispersion, enabling direct experimental observation. Notably, the hinge-state selectivity is modulated not only by bulk topology but also by boundary potentials engineered through unit-cell rotation. This rotation enables selective activation of hinge states, allowing precise control over their spatial distribution. Our work provides a versatile platform for exploring higher-order topological semimetals and opens opportunities for programmable acoustic waveguides and energy manipulation.

We develop a highly efficient framework for computing the thermal entropy in the doped Fermi-Hubbard model within the grand-canonical ensemble. The framework comprises four calculation schemes that express the entropy as path integrals in the parameter space of temperature, interaction strength, and chemical potential. The integrands involve only fundamental observables, including the total energy, fermion density, and double occupancy, which are readily accessible in a wide range of theoretical and numerical methods. We further derive useful Maxwell relations connecting the entropy to other quantities and present practical formulas for directly evaluating the grand potential. As an application, we compute the entropy of the doped Hubbard model in two and three dimensions, using the numerically unbiased auxiliary-field quantum Monte Carlo method. The test results show excellent agreement across the different schemes and quantitatively verify the Maxwell relations, confirming the reliability of the framework. In two dimensions, we further benchmark our entropy results in physically relevant parameter regimes against diagrammatic Monte Carlo calculations and observe excellent quantitative consistency between the two approaches. By providing an efficient and broadly applicable route for entropy evaluation, our work facilitates the thermodynamic characterization of complex correlated states in the doped Hubbard model.

Superconducting two-dimensional materials, and in particular few‐layer graphene, offer an exciting platform for low‐power electronics, yet the origin of their unconventional superconductivity remains an open question. Prevailing theories, primarily rooted in the Bardeen-Cooper-Schrieffer (BCS) framework that assumes electron-phonon interactions are the main mechanism of superconductivity, struggle to account quantitatively for the observed phenomena. Recent studies point to a plasmonic pairing mechanism in graphene systems; however, disentangling the relative contributions of phonon- and plasmon-mediated pairing remains challenging due to the lack of a satisfactory first-principles framework capable of accurately capturing dynamical screening effects in the electronic channel. Here, we present a theoretical framework that extends the quasiparticle self-consistent GW method to the superconducting phase by coupling it with the Eliashberg treatment of both phonon- and plasmon-mediated interactions. Our approach, termed superconducting quasiparticle GW (s-qpGW), is on par with the state-of-the-art Eliashberg theory of superconductivity when applied to bulk metals, and correctly predicts the absence of superconductivity in doped monolayer graphene. To differentiate s-qpGW from conventional Eliashberg approaches, we study a simple model system, graphene with an artificially enhanced density of states, and demonstrate that s-qpGW captures dynamical Coulomb screening effects in ways that standard BCS theory cannot.

We cure the lack of exchange-correlation (XC) spin torque in semilocal XC functionals by treating XC effects in the framework of spin-current-density-functional theory (SCDFT), and present the first projector-augmented-wave (PAW) implementation of this novel family of XC functionals: an U(1)$\times \mathrm{SU}\left(2\right)$ gauge-invariant SCDFT functional featuring a $2\times 2$ XC potential. While the framework can be applied to other XC functionals, the presented flavor of the SCDFT functional is based on Becke-Roussel exchange and Colle-Salvetti correlation. In addition to the $2\times 2$ spin density and kinetic-energy density, the XC functional depends on the $2\times 2$ spin-current density. The implementation requires the computation of the spin-current density within the PAW method and the variation of the XC energy with respect to it. The application to a ${\mathrm{Cr}}_3$ molecule and bulk MnO reveals (i) XC spin torque of the same order as obtained by methods including exact exchange, (ii) a counterintuitive contribution to the energy even in collinear ferromagnetic systems without spin-orbit coupling due to the semilocality of the magnetization, and (iii) a similar computational cost per electronic step as calculations that depend on, inter alia, the kinetic-energy density, but convergence within fewer electronic steps.

In the context of hybrid superconductor-semiconductor systems, Josephson junctions based on two-dimensional materials, such as graphene, offer promising opportunities because of their scalability and gate-tunable electronic properties. In this work, we investigate the inductive coupling between a quantum LC resonator and a superconducting loop embedding a short, ballistic, planar Josephson junction, with the graphene-based case as a representative example. Within a mean-field formalism, we analyze how the properties of the global system depend on the light-matter interaction coupling, the Fermi level of the two-dimensional material, and temperature. Our findings reveal that the current-phase relation can show features indicative of spontaneous time-reversal symmetry breaking. Furthermore, we determine the low-energy spectrum of collective hybridized light-matter excitations.

Bernal-stacked bilayer graphene (BLG) hosts correlated electronic phases tied to low-energy Lifshitz transitions at saddle points in its valence band. To access this regime, ultralow charge disorder and control over a vertical electric field are simultaneously required. Here, we employ a twist-decoupled monolayer (MLG) to bias a proximal BLG in the absence of an external displacement field ($D$). We thereby reveal threefold degenerate quantum Hall states at $D=0$, with multiple transitions driven by doping, magnetic and electric field. Spontaneous broken symmetry in the vicinity of the valence band edge is signaled by the emergence of quantum oscillations with anomalous frequencies and large quasiparticle mass. These results indicate that electronic interactions in BLG are preserved in presence of an atomically close MLG, while showcasing the potential of CVD-grown graphene multilayers for the exploration of correlated phases of matter.