Experimental validation of equation-of-state (EOS) models for high-energy-density applications typically involves measuring the shock Hugoniot, which helps constrain the high-pressure, high-density EOS. However, EOS measurements at below ambient density in the expanded regime are less common. Recent experimental advances allow the isentrope to be inferred from measurements of the density profile of an adiabatically expanding proton-heated plasma, offering the potential to assess various theoretical EOS models over a wide range of below-ambient density conditions. On the theoretical side, determining the expanded-regime EOS poses a considerable challenge for ab initio methods like density functional theory–based molecular dynamics (MD) due to the big simulation cells and large number of orbitals required to simulate these low-density, high-temperature conditions. We thus take a more computationally friendly approach by leveraging the power of MD driven by machine-learned interatomic potentials (ML-IAPs) trained on ab initio simulations. We directly simulate the adiabatic expansion of heated diamond at conditions relevant to experiments using large cells with up to 1.3 million atoms. These simulations, using several different variants of carbon ML-IAPs, are used to extract release isentropes and to study possible microscopic chemistry and phase transitions at play. These insights gained from our MD simulations can serve to guide the design and interpret observations of experiments.

The phenomenon of frustration greatly enriches the accessible physics of quantum magnets. With this in mind, we study the magnetism of ${\mathrm{NdCl}}_3$ using a combination of bulk property measurements and neutron scattering techniques. The low-temperature heat capacity reveals two magnetic transitions at $T_{N1}$ = 270 mK and $T_{N2}$ = 180 mK. However, much of the magnetic entropy is released above $T_{N1}$, manifesting as a broad peak centered at $T^{*}\approx$ 450 mK. A similar broad peak is observed in the magnetic susceptibility, which possesses a clear anisotropy; these data can be well fit using a one-dimensional XXZ model, yielding an antiferromagnetic nearest-neighbor exchange $J_{\mathrm{NN}}$ = –0.962(2) K and exchange anisotropy close to the Ising limit. Single-crystal elastic neutron scattering reveals highly anisotropic magnetic diffuse scattering above $T_{N1}$, confirming that quasi-one-dimensional, short-range, antiferromagnetic order is the origin of the broad peak in the heat capacity and magnetic susceptibility. Magnetic Bragg peaks characterized by a $\vec{k}$ = (0 0 $\frac{1}{2}$) propagation vector emerge below $T_{N1}$. Interestingly, the magnetic diffuse scattering persists for $T_{N2}<T<T_{N1}$, indicating a regime of coexisting short- and long-range order. The magnetic Bragg peaks exhibit an additional increase in intensity below $T_{N2}$ with no change in $\vec{k}$. Concomitantly, the diffuse scattering disappears, indicating the attainment of full long-range order. While the precise nature of the ordered magnetic ground state remains unresolved, the observed magnetic scattering indicates predominant $c$-axis moments with a small $ab$-plane component. We propose that the quasi-one-dimensional behavior and the coexistence of short- and long-range order are driven by frustration of exchange interactions with significant anisotropy.

Fabry-Pérot (FP) oscillation arises from interference between coherent paths induced by multiple reflections. In mesoscopic electronic systems, FP oscillation is commonly observed in various one-dimensional (1D) devices. However, in higher-dimensional systems, the presence of numerous transverse channels typically leads to dephasing, which suppresses the overall oscillation. To date, FP oscillation in two-dimensional electronic systems has been reported only in graphene-based devices and, more recently, in the $\mathit{pn}$ junctions of an inverted InAs/GaSb double quantum well. In the latter, electron-hole hybridized band structure plays a crucial role, generating many parallel 1D channels that satisfy nearly identical conditions for constructive interference. In this paper, we propose that this mechanism can be generalized to three-dimensional (3D) systems, such as the nodal line semimetals. We find that due to the spin texture in nodal line semimetals, the electron-to-hole scattering process, and consequently the FP oscillation, are significantly suppressed. However, by introducing ferromagnetic leads, the electron-to-hole scattering can be enhanced, thereby preserving the FP interference. Our results provide a promising way for the implementation of FP oscillation in 3D electric systems.

Topological insulator nanowires provide a versatile platform for studying the interplay between disorder, quantum interference, and symmetry-protected transport. We investigate quantum transport in disordered topological insulator nanowires threaded by an axial magnetic flux. From the length dependence of the conductance, we extract the localization length and characterize the flux-driven delocalization transition near half-integer flux quanta. We determine a localization-length exponent $\nu \simeq 2$, robust against variations of chemical potential and disorder strength, and relate this scaling to the asymptotic dominance of the protected helical channel. This value differs from the localization-length exponent of the integer quantum Hall transition, indicating that the transition is not described by integer quantum Hall critical scaling. Near integer flux quanta, we uncover an unexpected crossover from weak localization at low chemical potential to weak antilocalization at higher chemical potential, followed by a splitting and eventual suppression of the interference peak as the system enters the strongly localized regime.

We investigate nonstabilizerness, also known as “magic”, to understand criticality and exceptional points in non-Hermitian quantum many-body systems. Our focus is on parity-time ($\mathcal{PT}$)-symmetric spin chains, specifically the non-Hermitian transverse-field Ising and XX models. We calculate stabilizer Rényi entropies in their ground states using non-Hermitian matrix product state methods. Our findings show that magic exhibits unique and model-specific signs of phase transitions. In the Ising chain, it peaks near the regular Hermitian-like critical line but disappears across exceptional points. In contrast, in the XX chain, it reaches its maximum at the exceptional line where $\mathcal{PT}$ symmetry is broken. Finite-size scaling reveals that these effects become more pronounced with larger systems, highlighting nonstabilizerness as a sensitive marker for both quantum criticality and non-Hermitian spectral degeneracies. We also investigate magic in momentum space for the XX model analytically and find that it reaches a minimum around exceptional points. Our results indicate that magic takes extremal values at the exceptional points and serves as a valuable tool for examining complexity, criticality, and symmetry breaking in non-Hermitian quantum matter.

We investigate the metal-insulator transition driven by the onsite repulsive interaction $U$ in an altermagnetic Hubbard model defined on a Lieb lattice. Using the slave-rotor approach at half-filling, we find that the system exhibits a cascade of interaction-driven phase transitions. As $U$ increases, the system evolves from a normal metal to an altermagnetic metal, then to an altermagnetic insulator, and eventually to an altermagnetic Mott insulator characterized by the complete suppression of the quasiparticle weight. These phases are supported by the calculation of the electronic spectral function, which features spin-split bands in both the metallic and insulating regimes. However, the spin splitting becomes substantially suppressed in the Mott-insulating phase. Our results suggest that the observation of spin splitting in the spectral function of $d$-wave altermagnets with a Lieb-lattice-like structure may be limited to the weak-to-moderate correlation regime.

We present a revised atomistic picture of the order-disorder transition in the archetypal orbital-ordered perovskite material, ${\mathrm{LaMnO}}_3$. Our study uses machine-learning-driven molecular-dynamics simulations which describe the temperature evolution of pair distribution functions in close agreement with experiments. We find the orbital-disordered phase in ${\mathrm{LaMnO}}_3$ to comprise a mixture of differing structural distortions with and without inversion symmetry, implying a mixture of different orbital arrangements. These distortions are highly dynamic with an estimated lifetime of $\sim 40$ fs at 1000 K, and their fluctuations converge with the timescales of conventional thermal motion in the high-$T$ phase—indicating that the electronic instability responsible for static Jahn-Teller distortions at low temperature instead drives phonon anharmonicity at high temperatures. Beyond ${\mathrm{LaMnO}}_3$, our work opens an avenue for studying a wider range of correlated materials.

The electrical conductivity of high-pressure silicates profoundly influences the interior dynamics of rocky planets. Employing the Kubo-Greenwood formalism, we perform ab initio calculations of electronic conductivity in Fe-bearing post-perovskite under super-Earth mantle conditions, up to 4000 K and 500 GPa. Electronic structures are obtained via many-body perturbation theory, incorporating dynamical screening and correlations among localized Fe-$3d$ orbitals. In contrast to (Fe,Mg)O, for which metallization has been reported at comparable conditions, our results indicate that post-perovskite with Earth-like Fe contents is unlikely to metallize in super-Earth mantles via band-gap closure, yielding negligible low-frequency conductivity. Thus band conduction is negligible under the conditions examined. Small-polaron hopping is a plausible explanation for the larger measured total conductivity, but testing this hypothesis requires explicit calculations beyond the present band-conduction treatment.

Donor impurities in wide direct band gap semiconductors provide a promising platform for spin-photon quantum technologies by combining a donor spin qubit with optically addressable transitions. In ZnO, the shallow donor with the largest reported binding energy has long been associated with the $I_{10}$ bound exciton line, but its microscopic origin has remained unresolved. Here we demonstrate the controlled formation and identification of this donor as a Sn-Li complex through a combination of ion implantation, annealing, optical spectroscopy, and first-principles calculations. Resonant two-laser coherent population trapping measurements reveal an electron–${}^{119}\mathrm{Sn}$ hyperfine interaction of $392\pm 15\mathrm{MHz}$, establishing a coupled electron-spin-1/2, nuclear-spin-1/2 system with one of the largest hyperfine couplings reported for shallow donors in semiconductors. Density functional theory calculations show that a nearest-neighbor ${\mathrm{Sn}}_{\mathrm{Zn}}-{\mathrm{Li}}_{\mathrm{Zn}}$ complex has favorable formation energetics, donor character with the electron localized on Sn, and an extrapolated hyperfine interaction consistent with experiment. The large donor binding energy and excited-state structure indicate enhanced thermal robustness of the optical transition relative to conventional group-III donors, while the strong hyperfine interaction enables fast electron-nuclear spin control and prospects for direct nuclear-spin-photon interfaces. We further observe efficient optically induced nuclear spin polarization, highlighting a path toward nuclear spin initialization. More broadly, our results reveal how a donor-acceptor complex can access previously unexplored regimes of shallow donor physics, extending the design space of donor quantum defects beyond isolated substitutional dopants.

The order from quantum disorder (OFQD) effect was first discovered in frustrated quantum spin systems. Recently, OFQD was also found in Rashba spin-orbit-coupled (SOC) systems even on a square lattice. Here we study the role of OFQD in the experimentally realized weakly interacting bosonic quantum anomalous Hall system of spinor bosons in an optical lattice. We perform microscopic nonperturbative OFQD calculations and construct an effective action based on symmetry considerations. These two complementary approaches establish an OFQD-induced quantum critical regime at finite Zeeman field. In particular, we show that the competition between the OFQD-generated effective potential and the Zeeman field drives a continuous quantum phase transition from the canted-antiferromagnetic superfluid phase to the $Z$-ferromagnetic superfluid phase with dynamical exponent $z=2$. We further determine the associated finite-temperature quantum critical scaling and discuss experimentally relevant signatures in existing cold-atom platforms. Our results establish OFQD as a mechanism for an interaction-driven quantum phase transition in the bosonic quantum anomalous Hall system.

$\beta \text{−}{\mathrm{FeSi}}_2$ exhibits exceptional oxidation resistance, commonly attributed to the formation of a dense, protective ${\text{SiO}}_2$ surface layer; however, the atomistic pathway governing the emergence of this layer and the subsequent suppression of oxidation remains elusive. In this work, we develop an active-learning MACE interatomic potential for the reactive Fe-Si-O system and incorporate a Fermi-like potential wall to enable one-sided reactive molecular-dynamics simulations of $\beta \text{−}{\mathrm{FeSi}}_2$ surface oxidation. By analyzing 100 statistically independent trajectories, we find that self-limiting oxidation on both Si-terminated and Fe-terminated surfaces is consistently associated with the development of an extended connected Si-O network within the oxidized interfacial region. The Si-terminated surface passivates through direct oxidation of exposed Si atoms, whereas the Fe-terminated surface first undergoes Fe oxidation before oxygen reaches the subsurface Si-rich region and forms an extended connected Si-O network. Statistical analysis shows that Fe-O-Fe connectivity is either negligible or incomplete and does not constitute the primary passivating framework. Species-resolved density profiles ${\rho }_{\alpha }(z,t)$ reveal that oxidation proceeds through coupled oxygen incorporation, substrate-atom migration, and interfacial reconstruction, rather than simple inward oxygen diffusion into a static substrate. These results support a connectivity-based microscopic picture in which the development of an extended Si-O network is consistently associated with self-limiting oxidation of $\beta \text{−}{\mathrm{FeSi}}_2$ surfaces, and they provide a transferable computational protocol for exploring oxidation mechanisms in transition-metal silicides and related reactive materials.

Cavity quantum electrodynamics offers a route to control quantum phases by using vacuum fluctuations of confined electromagnetic fields. In particular, planar cavities based on polar van der Waals materials can generate strongly confined modes and are promising for controlling two-dimensional correlated materials. Recently, moiré materials have become central platforms for studying two-dimensional heavy-fermion systems and their quantum phase transitions. Kondo lattices provide a prototypical model for studying quantum phase boundaries, driven by competition between Kondo screening and the ordering of local magnetic moments. We show that a cavity-induced interaction can shift the quantum phase transitions between a heavy-fermion phase and an antiferromagnetic phase in a two-dimensional Kondo lattice through a momentum-dependent self-energy of the conduction bands. For the longitudinal projected field motivated by h-BN hyperbolic phonon polaritons, the self-energy favors Kondo hybridization and expands the heavy-fermion region. Transverse and circular in-plane model structures give distinct effects, with the transverse case relatively favoring the magnetically ordered phase and the circular case lying between the longitudinal and transverse cases. These results indicate that electromagnetic vacuum fluctuations can effectively modify the control parameters of strongly correlated two-dimensional Kondo materials.

Noncoplanar magnetic order in low-carrier-density semiconductors provides a platform on which spin-charge coupling can reshape the electronic structure and induce nontrivial topological phases. Motivated by the recent discovery of the four-sublattice triple-$q$ order in the magnetic semiconductor GdGaI, we study an effective theory that couples a Ga $4p$ hole pocket at the $\mathrm{\Gamma }$ point to three Gd $5d$ electron pockets at the $M$ points through four exchange channels. For the antiferromagnetic umbrella state with zero net magnetization, the model hosts trivial ($C=0$) and $C=\pm 4$ Chern insulator phases separated by metallic regions; by deriving an analytical low-energy theory at the $\mathrm{\Gamma }$ point, we show that the topological phase boundary is described by two degenerate double-Weyl semimetals, naturally explaining the $\mathrm{\Delta }C=4$ jump in the Chern number. In addition, a nodal-line-like state pinned near the Fermi level emerges in the absence of the $p\text{−}d$ exchange coupling, which separates the $C=\pm 4$ phases for $\theta =arccos\left(\frac{1}{3}\right)$ into two. Tuning the canting angle by an external magnetic field drives an insulator-to-metal transition out of the Chern insulator phase while leaving the trivial insulator largely intact, and stabilizes an additional $C=\pm 2$ Chern insulator phase when the uniform-magnetization exchange couplings become appreciable. These results identify GdGaI and its sister compounds as highly tunable platforms for realizing topological phases and field-induced metal-insulator transitions in clean magnetic semiconductors.

We study the phase diagram of interacting spinless fermions on the honeycomb bilayer at charge neutrality using large-scale quantum Monte Carlo simulations. In the noninteracting limit, the low-energy spectrum features quadratically dispersing bands that touch at the corners of the hexagonal Brillouin zone. Weak to intermediate interactions induce a splitting of each of the quadratic band touching points into four Dirac points, located along high-symmetry directions of the reciprocal lattice. Strong interactions lead to the formation of a layer-polarized charge density wave, which spontaneously breaks the ${\mathbb{Z}}_2$ layer inversion symmetry and opens an insulating gap in the spectrum. We show that the semimetal-to-insulator quantum phase transition as a function of interaction is continuous and characterized by emergent relativistic symmetry. Our results for the values of the correlation-length exponent $\nu$, the order-parameter anomalous dimension ${\eta }_{\varphi }$, and the fermion anomalous dimension ${\eta }_{\psi }$ agree with those of the theoretically predicted (2+1)-dimension Gross-Neveu-Ising universality class with eight two-component Dirac fermions within less than 5% deviation. We also determine the crossover scale as a function of interaction strength between the nonrelativistic semimetal state at high temperatures, characterized by dynamical critical exponent $z=2$, and the Dirac semimetal state at intermediates temperatures, characterized by $z=1$. Further reducing the temperature below the crossover scale at a fixed value of the interaction strength above the quantum critical point results in a classical ordering transition in the two-dimensional Ising universality class.

Square-lattice J-Q models provide a sign-problem-free setting for probing the quantum phase transition between Néel antiferromagnets and columnar valence-bond solids. We analyze this transition through the scaling of Lee-Yang zeros, computed within stochastic series expansion quantum Monte Carlo by reweighting configurations sampled near criticality in the presence of complex source fields. Benchmark studies of the dimerized Heisenberg model and the checkerboard J-Q model validate the method, yielding stable $\mathrm{O}\left(3\right)$ critical scaling in the former and clear spacetime-volume scaling in the latter, as expected for a first-order transition. Applying the same analysis to the J-Q models, we find a pronounced and systematic drift of the leading-zero scaling with increasing system size, consistent with an extended pseudocritical regime. The Lee-Yang scaling implies an effective scaling dimension ${\mathrm{\Delta }}_{\varphi }$ of the $\mathrm{SO}\left(5\right)$ order-parameter field that decreases with size and is consistent with vanishing in the thermodynamic limit. Such behavior lies below the scalar unitarity bound of any unitary relativistic conformal field theory in $2+1$ dimensions and enforces inverse spacetime-volume scaling of the zeros, the hallmark of a first-order transition. These results support a weakly first-order interpretation of the Néel–VBS transition and establish the finite-size Lee-Yang zeros as a sensitive, symmetry-resolved diagnostic of pseudocriticality and transition order in the J-Q family.

We show that a radially symmetric, nonresonantly pumped spinor exciton-polariton condensate can acquire chirality without a rotating drive, chiral geometry, or pump orbital angular momentum. Spin relaxation in a two-reservoir system shifts the reservoir-induced blueshift relative to the gain profile, creating an effective non-Hermitian chiral potential. A reduced angular-mode theory reveals tunable exceptional points and nonreciprocal coupling between counterrotating modes. Full driven-dissipative Gross-Pitaevskii simulations show that this hidden chirality enables all-optical formation of spin-selective half-vortices.

The Einstein relation linking charge carrier mobility and diffusion coefficient is a fundamental principle of charge transport. However, in disordered organic semiconductors, energetic disorder and carrier filling in localized states lead to a concentration-dependent diffusivity–mobility ratio described by the generalized Einstein relation (GER). Carrier-carrier interactions may further modify carrier occupation and transport behavior in these systems. However, their role in determining GER remains largely unexplored, especially in multicomponent systems. Here, using three-dimensional kinetic Monte Carlo simulations, we investigate the impact of Coulomb correlation on the GER in pure materials, binary systems, and ternary systems. We show that Coulomb correlation systematically modifies the GER, with the magnitude of the modification regulated by the relative permittivity, host-guest energy offset, guest concentration, temperature, and energetic disorder. The underlying mechanism is an interplay between energy-selective filling and Coulomb-induced carrier redistribution. In hostguest systems, the pronounced peak structures arising from multistep filling are progressively modified by Coulomb correlation. These results provide a comprehensive understanding of how Coulomb correlation governs the GER in disordered organic semiconductors and offer valuable insights for parametrizing diffusivity and mobility in drift-diffusion simulations of organic electronic devices.

Computational studies of the thermodynamic properties of materials at the mesoscopic and macroscopic scales—involving lengths and times of at least $\mu \mathrm{m}$ and $\mu \mathrm{s}$, respectively—rely on a coarse-graining approximation such that only a few relevant collective variables are treated explicitly. Those variables typically take the form of fields defined everywhere in space (e.g., a polarization field in dielectric or ferroelectric media) or macroscopic quantities when spatial inhomogeneities can be treated implicitly (e.g., the volume average of the electric polarization). The free energy is usually expressed as a Landau-type potential whose temperature-dependent minima track stable states, characteristic equilibrium fluctuations being implicitly accounted for. Further, the response of the system to external perturbations, and its relaxation toward thermal equilibrium, are described in terms of simple equations of motion governed by effective inertial and viscous-damping constants. There is considerable literature on the problem of deriving Landau-type free energy potentials, from either experiment or predictive atomistic simulations, including recent efforts to develop systematic machine-learning approaches that we denote “third principles.” Much less attention has received the calculation of the effective constants defining the time-dependent Landau equations and the corresponding nonequilibrium macroscopic or mesoscopic dynamics. Here we tackle that problem, describing a protocol that allows us to compute the temperature-dependent inertial and damping coefficients associated to the electric polarization in representative soft-mode ferroelectric ${\mathrm{PbTiO}}_3$. Our scheme follows usual approaches to analyze experimental vibrational spectra. It relies on standard equilibrium molecular-dynamics simulations and is therefore readily applicable with modern machine-learned interatomic potentials. Our results also allow us to comment on common assumptions in the literature of effective dynamic treatments and phase-field simulations of ferroelectrics and related materials.