Papers

Identifying materials platforms in which dilute carriers experience strong Coulomb interactions is a central challenge in the search for interaction-driven quantum phases. In such systems, weak carrier screening can promote a variety of collective instabilities beyond the conventional Fermi liquid paradigm, including superconductivity, Wigner crystallization, and odd-parity electronic order. Experimental realizations of such dilute, strongly interacting electronic systems remain rare in crystalline materials. Here we report a spontaneous odd-parity phase transition in the phosphide semiconductor family $\textit{Ln}$Cd$_3$P$_3$ ($\textit{Ln}$ = La, Ce, Pr, Nd). Using optical second harmonic generation, we observe the onset of bulk inversion and rotational symmetry breaking accompanied by the emergence of an in-plane polar axis. Second harmonic microscopy reveals three domain variants related by 120$^\circ$ rotations, while ultrafast transient reflectivity measurements uncover a pronounced electronic reconstruction across the transition. Remarkably, the ordered phase appears only in lightly self-hole-doped compounds and is absent in insulating SmCd$_3$P$_3$, indicating an essential role for itinerant carriers despite their extremely low concentration. Guided by density functional theory, we develop a four-band model of the valence states and show that modest interactions can stabilize odd-parity electronic order. The resulting phase combines a spontaneous Fermi surface distortion with a momentum-dependent bilayer polarization that breaks inversion symmetry. Our results establish a route to interaction-driven parity breaking in dilute-carrier semiconductors and identify honeycomb bilayer systems as a promising platform for odd-parity electronic phases.

Exchange bias at ferromagnet-antiferromagnet interfaces underpins magnetic memory, spintronic devices, and nanoscale electromagnetic technologies, yet its behaviour in complex nanoscale heterostructures remains poorly understood. Here we uncover how exchange bias emerges in functional multiphase metal-oxide nanoparticles by combining gas-phase synthesis, advanced magnetic characterisation, and first-principles-informed spin-dynamics simulations. Using Ni-Cr/NiO nanoparticles as a model system, we show that exchange bias is governed not simply by the presence of ferromagnetic and antiferromagnetic phases, but critically by their nanoscale spatial distribution and interfacial topology. At 10 K, significant negative exchange bias (0.8 kOe) and coercivity enhancement (1.4 kOe) was exhibited; both decreased due to either Cr-segregation (at low Cr content) or to Cr accumulation inside the core (at high Cr content). The resulting competition between magnetic phases produces a temperature-driven inversion from negative to positive exchange bias and a crossover from exchange-dominated to dipolar interactions. By linking density-functional-theory calculations directly to spin-dynamics simulations of nanoparticle ensembles, we establish a predictive framework for designing exchange-coupled nanomagnets capable of operating beyond the superparamagnetic limit.

Biomolecular condensates formed by phase separation often exhibit viscoelastic behavior, yet their shape recovery and fusion dynamics are frequently interpreted using purely viscous models. Here, we develop a unified theoretical and computational framework to quantify how viscoelasticity governs these two processes. We combine analytical theory for small-deformation shape recovery with axisymmetric finite-element simulations based on the Oldroyd-B constitutive model to systematically investigate both shape recovery and droplet fusion under comparable conditions. Our results show that, although both processes are driven by capillary forces, they are fundamentally distinct in their underlying physics. Shape recovery is governed by global viscocapillary relaxation of a single connected interface and follows single- or multi-exponential decay depending on the relative magnitude of the viscocapillary timescale and the stress relaxation time. In contrast, droplet fusion is intrinsically a multistage process involving localized curvature-driven neck formation, rapid bridge expansion, and a transition to global relaxation. We demonstrate that viscoelasticity introduces an additional intrinsic timescale that governs the competition between capillary driving and stress relaxation, characterized by the Deborah number. This leads to enhanced intermediate-stage fusion dynamics and modified relaxation behavior compared to Newtonian droplets. Furthermore, we show that the presence of an exterior fluid introduces additional hydrodynamic dissipation, significantly slowing the fusion process. Finally, we compare the computationally predicted droplet fusion in the Newtonian and viscoelastic cases with a stretched-exponential empirical formula. Deviations observed in viscoelastic regimes highlight the limitations of purely viscous descriptions and the need for models incorporating stress relaxation.

Chromium oxide (Cr$_2$O$_3$) is widely considered a $p$-type transparent conducting oxide despite ongoing debate regarding its intrinsic transport character. Here, we resolve this question by computing phonon-limited electron and hole mobilities using the ab initio Boltzmann transport equation. We find that electron mobility systematically exceeds hole mobility over a wide temperature range, demonstrating that Cr$_2$O$_3$ is intrinsically $n$-type. Analysis of scattering mechanisms reveals that scattering with phonons affects electrons and holes similarly, and that the mobility asymmetry originates from the electronic structure, namely the larger effective mass and multi-valley character of the valence band. The intrinsic $n$-type character, combined with moderate hole mobility, enables bipolar transport and revises the role of Cr$_2$O$_3$ in transparent electronics. Additionally, our results on mobility complement previous studies on defect formation indicating that the commonly observed $p$-type behavior is extrinsic. These insights provide a complete chemical-transport paradigm for Cr$_2$O$_3$, re-evaluating its role in functional transparent electronic and magneto-optoelectronic applications

We present a comprehensive study of quadrature squeezing in a quantum well laser based on a fully quantum Langevin approach. We compute the frequency-resolved squeezing map of the laser field and identify optimal squeezing curves, revealing, for the first time to our knowledge, both frequency-dependent squeezing and complex or hidden squeezing in a semiconductor laser. We further analyse the role of the linewidth enhancement factor (alpha-factor) in the emergence of these features. Our results establish semiconductor lasers as a platform for the generation of non-classical light and open new perspectives for their application in quantum communication and sensing.

We study the effect of superconducting fluctuations on the spin susceptibility and NMR relaxation rate in noncentrosymmetric two-dimensional materials above the superconducting transition temperature, considering arbitrary strength of impurity scattering. Employing a microscopic model with linear Rashba spin-orbit coupling, we show that superconducting fluctuations give rise to a direct contribution to the spin susceptibility through fluctuation-induced Cooper pairs. This fluctuation-driven magnetoelectric effect is possible even for purely $s$-wave singlet pairing, a mechanism that is forbidden in centrosymmetric systems. It competes with the reduction of the susceptibility below the Pauli value arising from the combined effects of the suppression of the density of states and quantum-interference localization processes. In contrast, superconducting fluctuations enhance the NMR relaxation rate above its normal-state Korringa value, with spin-orbit coupling providing an additional amplification of this effect.

The quest for new superconductors is of both fundamental and technological importance. Recently, an artificial intelligence method correctly predicted PtPb$_3$Bi to be a superconductor. In this work, we find superconductivity in the newly synthesized $M$Pb$_{4-x}$Bi$_x$ ($M$ = Au, Pd, and Rh), of which PtPb$_3$Bi is a member. When $M$ = Ni, whose radius is considerably smaller, the structure instead collapses into the different, Pb-substituted NiBi$_3$ type. Interestingly, the stoichiometric parameter $x$ shifts across the three compounds to keep the total valence electron count close to 20 per formula unit. The superconducting transitions occur at 4.9, 4.2, and 3.4 K, for $M$ = Au, Pd, and Rh, respectively. Using electrical resistivity, magnetization, and specific heat measurements, we establish the bulk nature of the superconducting state and determine the critical fields, characteristic length scales, and anisotropy ratios. All three compounds are moderately anisotropic type-II superconductors, with modest upper critical field anisotropies of $H_{c2}^{\parallel c}/H_{c2}^{\perp c} \approx 1.2$ to $1.5$. These results establish $M$Pb$_{4-x}$Bi$_x$ as a family of anisotropic superconductors and a platform for studying how site disorder and Pb-Bi mixing govern superconductivity in heavy-element intermetallics.

In this work, we discuss how to determine and implement feasible optimal observables for a metrology protocol that saturates the quantum Fisher information (QFI) bound. In particular, we focus our study on a simple protocol, namely the method of moments (MoM). We first demonstrate that the symmetric logarithmic derivative (SLD) operator, a Hermitian observable, once implemented in the MoM, saturates the QFI bound. However, the SLD is generally too complex and typically non-local, rendering its direct experimental realization unfeasible. To overcome this limitation, we explore its structure in a specific sensing model - a Floquet time crystal (FTC) acting as an ac field sensor - and show that the SLD can be approximated by substantially simpler observables, such as the bare spin magnetization or a parity observable, for different relevant initial state preparations. We further corroborate our theoretical predictions in a nuclear magnetic resonance system operating as an FTC sensor, employing experimentally motivated parameters to simulate its performance in a state-of-the-art implementation. In general, our results establish a practical route toward near-optimal metrology in FTC sensors, where the inaccessible SLD operator can be replaced by simpler observables while retaining quantum-enhanced sensitivity.

We investigate the mineral bobkingite, \ce{Cu5(OH)8Cl2(H2O)2}, as a potential realization of the sawtooth chain. Using ab initio methods, we estimate the magnetic exchange couplings and find that bobkingite hosts quasi-one-dimensional sawtooth chains, with residual three-dimensional interactions strongly suppressed by the crystal geometry. Examining the full exchange network, we find that the classical model exhibits an extensive manifold of nearly degenerate states with emergent two-dimensional character, which spin-wave theory shows to persist to leading order in quantum fluctuations as Ising degrees of freedom. Unlike other sawtooth candidates, bobkingite has negligible vertical interchain coupling, preserving a one-dimensional degeneracy even in the presence of ordering, suggesting that any long-range order is weak. Thermal fluctuations may thus stabilize a finite-temperature classical spin liquid regime, with a cascade of transitions upon cooling into successively lower-dimensional degenerate states, making bobkingite a compelling platform for exploring sawtooth chain physics.

We show that the phonon Hall viscosity at zero magnetic field is a natural probe of altermagnetism. First, we demonstrate that the finite elements of the Hall viscosity tensor unambiguously distinguish altermagnets from ferromagnets and conventional antiferromagnets. We then microscopically compute the Hall viscosity in models for d-wave and g-wave altermagnets, and find a strong sensitivity to electronic spectrum features such as gapped Dirac points and Lifshitz transitions. This sensitivity reflects a strain-space Berry curvature monopole, which contrast to the multipolar character of the standard momentum-space Berry curvature in altermagnets. Since the Hall viscosity can be probed experimentally through magneto-acoustic measurements, it provides a compelling method to probe the broken symmetries and topology of insulating altermagnets.

Odd diffusion is a hallmark of chiral active matter, generating currents transverse to density gradients. Existing theories rely on a linear antisymmetric transport coefficient that exists only in two dimensions, raising the question of whether odd diffusion can occur in isotropic three-dimensional systems. Here we show that such transport is possible through a nonlinear constitutive law. Symmetry considerations reveal that the three-dimensional Levi-Civita tensor permits a leading order isotropic odd current at second order in the density gradient expansion and only in multicomponent systems. The resulting transport generates boundary-driven rotational currents, finite vorticity, and enstrophy despite the absence of external torques or preferred directions. We show how such a constitutive law derives from a microscopic model of particles interacting through nonreciprocal three-body forces using the Dean–Kawasaki coarse-graining procedure. These results establish a minimal framework for odd transport in isotropic three dimensions.

What does it mean for a mixed-state topological phase to be chiral? Mathematically, chirality can be sharply characterized through the symmetry algebra of the mixed state. Physically, however, the question is far more subtle. In pure states, chirality in topological phase is tied to a web of familiar diagnostics, involving bulk-boundary correspondence, a gapless entanglement spectrum, a nontrivial modular commutator, and a quantized thermal Hall response. We show that none of these diagnostics remain reliable in mixed states. Instead, for decohered topological phases with a known error-free parent state, we propose two relative-entropy-based measures that can diagnose chirality, with one of them further extracting the chiral central charge. As a concrete example, we use these measures to analyze the $em^2$-decohered $\mathbb{Z}_3$ toric code, identifying the chirality transition to be in the random-bond Potts class for the particle-hole symmetric channel, and the polarized random bond Potts class for asymmetric channels. Our results emphasize how mixed-state topology demands intrinsically new diagnostics beyond direct analogues of pure-state probes.

Quantum annealers are supposed to follow adiabatically the ground state of a system as its Hamiltonian slowly interpolates between a trivial phase and a non-trivial one; the non-trivial ground state being the solution to an optimization problem. Overwhelmingly, their performances are measured in terms of how well or fast the optimization problem is solved. While pragmatic, this approach is inherently brittle as it strongly depends on the problem considered and the classical algorithm used as the reference benchmark. Here, we propose a quantity that not only measures the end result but also the quality of the actual quantum annealing process itself. Our metric is the quantum annealing counterpart of the fidelity-per gate of gate-based quantum computers. It takes the form of an accuracy $\epsilon$ for the equation of state of the annealer. We calculate benchmark values of $\epsilon$ using two variants of the simulated quantum annealing technique for Rydberg atoms systems. Our first approach uses variational quantum Monte-Carlo with an ansatz inspired by thermal annealing. It suggests that within $\epsilon \sim 10^{-2}-10^{-3}$, a quantum annealer is indistinguishable from its thermal classical counterpart. Critically, we could reach this precision up to $100,000,000$ atoms on a single CPU. Our second approach (based on Green function quantum Monte-Carlo) reaches accuracies around $\epsilon \sim 10^{-4}$ and we have run it up to $100,000$ atoms. These results outperform current Rydberg atom quantum annealing experimental platforms in both precision and size by orders of magnitude and put severe constraints for future hardware.

We introduce a framework of constructing topological subsystem codes based on the class of anticommuting quantum spin liquids described in [Phys. Rev. B 113, 064402 (2026)]. A canonical model from this class can be considered as a spatial modification of the toric code that voids its stabilizer code property. Rather, these models contain an extensive set of anticommuting local conserved operators that lead to an extensive ground state degeneracy. This degeneracy forms the basis of the subsystem degrees of freedom in the associated quantum error correcting code. The code inherits the many-body topological order of the quantum spin liquid, making it a topological subsystem code. We present two concrete and detailed examples for constructing these codes on a square lattice and a kagome lattice geometry, requiring weight-4 and weight-3 local check operator measurements respectively. In contrast to other subsystem codes, a unique property of these codes is the presence of an extensive number of local gauge qubits that are left undisturbed by the check operators apart from the logical qubits. Our construction provides a template for generating this new category of topological subsystem codes on different lattice or graph geometries, suitable for implementation on various quantum hardware platforms.

We investigate the odd-even staggering in the harmonically-trapped unitary Fermi gas at large particle-number charge $Q$. Using both a large-$N$ BdG description and a complementary large-charge EFT method, we show that for odd particle number the extra fermion forms an edge-localized quasiparticle near the Thomas-Fermi surface rather than a bulk excitation. In the edge limit, the microscopic BdG problem reduces to a universal coupled Airy system whose lowest positive eigenvalue fixes the leading odd-even splitting energy, $\chi\,\xi^{1/6}(24Q)^{1/9}\,\hbar\omega + \cdots$ where $\xi$ is the Bertsch parameter, and $\chi$ is a universal edge coefficient. The associated EFT describes a fermionic mode confined to the boundary and coupled to the superfluid Goldstone field, reproducing the same $Q$ scaling while introducing a dependence on two low-energy constants. Finally, we numerically compute the spectrum and confirm the predicted scaling and localization properties.

We consider a one-dimensional model for a $p$-wave magnet within the bosonization framework. The model consists of itinerant electrons described by an extended Hubbard model coupled to a chain of localized moments through the Kondo exchange. The classical ground state of the local-moment system captures the salient features of an odd-parity magnet. By bosonizing the coupled system, a description in terms of coupled Luttinger liquids follows, giving rise to a rich weak-coupling phase diagram. It is shown that the spin chain develops quasi long-range order consistent with the combined time-reversal and translation symmetry defining the $p$-wave magnet. We highlight the peculiar role played by this order in establishing a commensurability condition on the electronic filling under which additional interactions appear in the bosonic field theory. It is demonstrated that these interactions endow the electron spectral function with a pronounced $p$-wave character. Away from commensurate filling, these interactions are rendered irrelevant and the ensuing $p$-wave character is lost.

We rewrite a lattice model of the four-dimensional Chern insulator as a family of translationally-invariant infinite chains over the three-dimensional Brillouin zone and compute its higher three-form Berry curvature using infinite matrix product states (iMPS). We calculate the topological phase diagram of the associated Dixmier–Douady–Kapustin–Spodyneiko (DDKS) number as a function of the model's mass term, and show that it is exactly congruent to the phase diagram in terms of the second Chern number, the analytic expression of which is known for this particular model. This agreement demonstrates that higher Berry curvature can be used to compute second Chern numbers in a manifestly quantized manner. Motivated by the connection between the second Chern form and the Chern–Simons axion coupling, we study magnetoelectric coupling in three dimensions and its relation to higher Berry phases.

We give a thermodynamic-limit account of Dicke models with one cavity mode coupled collectively to interacting matter. Integrating out the cavity yields an exact self-consistent functional of the magnetisation $m$, $\tilde e(m) = \lambda m^2/2 + e_{\rm mat}(\lambda m)$: a classical penalty on the bare-matter energy $e_{\rm mat}$ in the self-consistent field $h = \lambda m$, with $\lambda = g^2/(2\omega_c)$ the collective coupling. Supplying only that scalar field, the photon creates no phase the matter does not already possess. States holding a minimum form one connected curve, $\lambda(m) = \mu_{\rm mat}^{-1}(m)/m$, so superradiant first-order transitions are folds of one equation of state not crossings of disjoint sheets, and a fold can straighten into a continuous line. The remaining rules are local, each with a spectral counterpart: onset by the leading singularity of $e_{\rm mat}$ (a softening polariton), order by one bare response – the Landau quartic, or a divergent susceptibility forcing a Larkin-Pikin (LP) fold. For the Dicke-Ising model the Landau coefficients are exact, giving in closed form the second-order boundary and both zero-quartic fields, one tricritical; a $1/d$ expansion maps all four phases, with the AS-PS transition first order for $d\le d_{uc}=3=4-z$ (LP) and tricritical points in the $(d,\epsilon)$ plane above. At the degenerate quadruple point the matter is a Rydberg-blockade chain, solved by strict-blockade iDMRG: the antiferromagnetic superradiant (AS) phase persists as a finite 1D wedge, first order into the corner. Other magnets: the triangular antiferromagnet keeps a continuous superradiant-superradiant line (3D-XY, no fold forced); the compass chain a BKT-functional onset; the Heisenberg and XX chains, via a conserved operator, a spectrally silent first-order onset; and the Dicke-Heisenberg diagram an exact tricritical point at the saturation corner.

In this work, we develop two many-body quantum electrodynamic methods to calculate the ground-state energies of strongly coupled light-matter molecular systems. Specifically, we extend the second-order many-body Green's function theory (GF2) for electronic systems to incorporate electron-boson couplings. We employ two ansätze to treat the bosonic part of the system, namely the coherent-state (CS) and Lang-Firsov (LF) transformed vacuum state. These are combined with the GF2 method to construct two new approaches, which we refer to as CS-GF2 and LF-GF2. We benchmark CS- and LF-GF2 by studying various molecular systems inside an optical cavity. We investigate $\mathrm{H}_2$ and $\mathrm{LiH}$ potential energy surfaces, keto-enol tautomerization energy barrier, van der Waals interactions between two $\mathrm{H_2}$ molecules and the torsional potential energy surface of the ethylene molecule, $\mathrm{C_2H_4}$. Both methods provide similar energy profiles, with relatively small differences between CS-GF2 and LF-GF2. Comparisons with the reference calculations also reveal remaining limitations at stretched bond lengths and near the twisted ethylene configuration. We additionally benchmark CS-GF2 against exact diagonalization for a two-site Hubbard-Holstein model and observe that it closely reproduces the coupling-induced energy change in the weakly interacting regime while improving upon CS-MP2 in the strongly interacting regime. Overall, the results demonstrate that CS-GF2 and LF-GF2 provide self-consistent descriptions of correlated molecular electron-boson systems, offering a many-body Green's function alternative for studying ground-state cavity-modified systems.

We study the photogalvanic effect in Weyl semimetals under a magnetic field, focusing on the shift current. Using the Kubo formalism for an ideal, clean Weyl node at zero temperature, we derive a general analytic expression valid for arbitrary light frequency, Fermi energy, and magnetic field strength. We identify a series of resonances that can be probed experimentally. To complement the microscopic analysis, we employ the semiclassical Boltzmann approach, which allows us to incorporate finite scattering phenomenologically. Unlike most previous studies using this method, we do not treat the magnetic field perturbatively; instead, we solve the Boltzmann equation for a Weyl node exactly within the limits of validity of the semiclassical theory. Our solution reproduces the low-frequency resonances and elucidates the role of finite scattering.

We propose altermagnetic semiconductors as a platform for field-free, all-electrically controlled spin qubits in gate-defined quantum dots. The momentum-dependent spin splitting of an altermagnet produces a Zeeman-like qubit splitting whose magnitude and sign are set by the dot ellipticity, enabling local frequency tunability without external magnetic fields or micromagnets. Because the splitting is tied to a fixed altermagnetic quantization axis, electric-field noise is longitudinally suppressed at leading order, while quantization-axis fluctuations couple transversely and therefore cause relaxation rather than pure dephasing. The compensated magnetic order also avoids stray fields, making the platform naturally compatible with superconducting resonators and dispersive circuit-QED readout through the qubit's spin-dependent electric dipole. Starting from an effective quantum-dot model, supported by a microscopic lattice model, we derive the single- and two-dot Hamiltonian models. We show that electric-dipole spin resonance enables single-qubit control, while tunable exchange and electrically addressable qubit frequencies realize fSim two-qubit gates. The same double-dot architecture also supports singlet-triplet qubits with electrical control of both exchange and splitting gradients, removing the need for micromagnets or nuclear-polarization gradients. These results establish altermagnetic quantum dots as a route to field-free spin qubits with intrinsic electrical tunability and enhanced dephasing protection.

Electronic excitations in solids are commonly described within a hierarchy in which the excitonic Hamiltonian is defined first and the lattice acts later through renormalization, relaxation, and dephasing. This picture assumes that the optically accessible excitonic manifold is already present at the moment of photoexcitation. Here we show that this assumption fails in a soft polar semiconductor. Using femtosecond coherent multidimensional spectroscopy on lead-halide perovskite nanocrystals, we observe quantum back-action between an electronic excitation and a collective lattice-polarization field that expands the excitonic Hilbert space in real time. The optical pulse first prepares an excitonic polarization, X1. A second configuration, X2, emerges only after the polaron field develops, while coherent X1-X2 coupling appears at later times. State formation and coherence formation are therefore resolved as distinct stages of quasiparticle formation. In contrast, CdSe quantum dots exhibit the conventional limit in which excitonic states and couplings are present at time zero and are only weakly perturbed by phonons. The observed diagonal and anti-diagonal splittings increase with nanocrystal size and correlate with radiative oscillator strength, opposite to expectations from simple quantum confinement. A dynamical polaron-field model describes the lattice polarization as an order parameter that expands the optically accessible manifold and generates time-dependent coherent coupling. These results show that strong system-bath coupling can actively create excitonic states and the coherent manifold in which they evolve.

Deterministic quantum light sources emitting at telecom wavelengths with vanishing fine-structure splitting (FSS) are essential components for scalable quantum communication. While self-assembled Stranski-Krastanov (SK) quantum dots (QDs) are high-quality emitters, their random positioning and shape-induced anisotropy typically limit their use in entangled-photon applications. In this work, we demonstrate site-controlled SK growth where InAs/InP QDs nucleate at the symmetric apexes of truncated InP nanopyramids. Confining adatom diffusion to a small, symmetric nucleation area suppresses anisotropic growth, promoting the nucleation of highly symmetric QDs with FSS reduced to values below our statistically validated resolution limit of $9.2~\mu$eV. At the same time, lithographically defined nucleation sites enable deterministic control of the QD position, overcoming the limitations of conventional SK growth. The high structural quality of single symmetric QDs is evidenced by the single-photon character of the emission ($g^{(2)}(0)=0.07^{+0.27}_{-0.07}$) spanning the S, C, and L telecom bands, with no evidence of lithography-induced defects affecting emission dynamics. These results demonstrate that tailoring QD symmetry through nanopyramid growth engineering provides a route toward site-controlled emitters suitable for entangled photon generation and integrated quantum photonics devices.

Midway through an ordinary pretraining run, a small language model learns the pronoun-gender rule: cued with a girl's name ("Sue cried because"), it resolves the next pronoun to she, generalizing to held-out probes (0.94 by step 925). By step 3,500 the same model scores near zero on the same probes, although the rule's evidence is still in the training data. We call this within-run reversal natural ungrokking: the corpus decides, with no trace in the loss curve, which learned rules a model keeps. Which rules survive is predictable from one corpus statistic: how often the training stream shows the rule winning. Across un-intervened runs (two corpora, three budgets, three seeds), support frequency decides a rule's fate; the data-to-parameter ratio only modulates how deeply a doomed rule falls. The same emerge-then-collapse dynamics appear in public Pythia checkpoints, collapse depth ordered by model scale as predicted. The forgetting is a displacement: a competing surface pattern out-competes the rule, and the log-probability margin between them crosses zero within 100 training steps of the behavioral collapse. Control over this fate is asymmetric: the same edit that destroys a rule on demand cannot restore it. Flipping support to counter-evidence in place kills the rule with monotone dose-response in two unrelated rules; but injecting support back, even to 450 times the level that naturally sustains it, buys no recovery. Every confirmatory threshold and prediction was pre-registered before the data it governed was read.

The altermagnetic nature of rutile RuO2 remains under active debate: bulk measurements indicate a nearly nonmagnetic ground state, whereas thin-film studies have reported symmetry-dependent transport signatures consistent with altermagnetism. Here, we provide experimental evidence that altermagnetic spin splitting in RuO2 is a strain-stabilized emergent state rather than an intrinsic bulk property. Angular-resolved spin-torque measurements reveal a symmetry-selected spin Hall response characteristic of altermagnetic spin splitting, which is strongest in the strained regime but progressively suppressed as the lattice relaxes toward the bulk limit. Complementary magnetic measurements further reveal enhanced coercivity and exchange-bias behavior exclusively in strained films, indicating the emergence of a strain-stabilized magnetic state. First-principles calculations reproduce the strain-dependent evolution of the Neel order and spin-split electronic structure, supporting the experimental observations. Together, these results establish altermagnetic spin splitting in RuO2 as a strain-stabilized emergent state and provide a unified explanation for the long-standing discrepancy between bulk and thin-film observations.

As advanced nuclear reactors demand novel irradiation-tolerant materials, this study investigates the radiation damage and mechanical degradation of the promising WTaCrV refractory high-entropy alloy (RHEA). To isolate complex nanoscale chemical effects, we propose an atomistic modeling strategy comparing Average-Atom (AA), random solid-solution (RSS), and local chemical order (LCO) configurations using newly developed interatomic potentials. Collision cascades simulations reveal that the number of Frenkel pairs follow NRSS > NLCO > NAA at the same radiation dose. While the RSS effect accelerates defect generation due to rugged energy landscapes, LCO enhances lattice cohesion to mitigate radiation damage. Despite more primary defects in the RSS and LCO configurations compared with the AA configurations, the RSS and LCO effects can suppress radiation-induced mechanical degradation. Irradiation severely degrade the homogenized AA model but exert a limited impact on the strength and flow stress of the RSS and LCO models. This exceptional resistance is driven by inherent lattice distortion resulting from interactions among different alloy elements, which outweighs point defect induced lattice disruptions. Moreover, the complex interactions between deformation twins and point defects cause confined plastic flow, elevating flow stress in the RSS and LCO models. The findings provide atomistic guidance for performance assessment of next-generation structural materials for extreme nuclear environments.

Uniform spin-orbit coupling in an open single-band Hubbard chain is an exactly removable \(SU(2)\) gauge field at the Hamiltonian level, but not at the level of laboratory-frame spin correlations. We study this separation using density matrix renormalization group calculations for the repulsive one-dimensional Rashba-Hubbard chain. For open boundary conditions, a site-dependent spin rotation maps the model with hopping \(t\) and Rashba spin-orbit strength \(\lambda\) onto the ordinary Hubbard chain with renormalized hopping \(t_\lambda=\sqrt{t^2+\lambda^2}\). Consequently, charge and energy diagnostics are affected only through the bandwidth renormalization, which is quadratic in weak \(\lambda/t\). Spin correlations, however, respond already at linear order because the same transformation rotates the local spin basis by the wave vector \(k_{\rm so}=2\arctan(\lambda/t)\). We use DMRG to verify this observable consequence across the filling diagram of finite open chains. The filling structure follows the gauge-equivalent Hubbard model, whereas the spin structure factor shows the predicted spin-orbit sidebands. A dominant Hubbard-chain magnetic wave vector \(k_0\) is transformed into components at \(k_0\pm k_{\rm so}\), folded into the open-chain Brillouin zone. At half filling, where \(k_0=\pi\), the two sidebands fold onto a single, in-plane, spin spiral wave with \(k=\pi-k_{\rm so}<\pi\). Away from half filling, the incommensurate Hubbard spin response splits into two distinct spin-orbit-shifted components, producing a real-space beating pattern. Our results provide a filling-resolved tensor-network benchmark for the exactly removable limit of one-dimensional spin-orbit coupling, and establish a controlled reference point for ladders, multiorbital chains, rings, proximitized wires, and higher-dimensional Hubbard systems where spin-orbit coupling can no longer be gauged away.

The coherent, periodic energy transfer between light- and matter excitations characterizes the strong coupling regime of cavity exciton-polaritons, resulting, in the simplest case, in a Rabi-doublet in the spectral domain. We demonstrate a peculiar regime of strong light-matter coupling, which arises when photonic cavity modes couple to an ultra-thin excitonic mirror. We embed a 12 nm J-aggregated thin film in an open microcavity and tune the coupling strength from weak to the onset of ultrastrong coupling. At resonance, the excitonic mirror selectively changes dielectric to metallic field boundary conditions adding a 2{\pi} phase, which links optical cavity modes of different order. Our work gives an exciting perspective to ultra-fast cavity switches and photonic devices based on excitonic optical elements.

In altermagnets that exhibit anomalous Hall effect, the small remanent magnetization exists but has been treated as too small to be relevant to the Hall response. In this work, we point out that this dismissal is incomplete because the generalized Středa relation ties the intrinsic anomalous Hall conductivity ($\sigma_{xy}$) to the orbital magnetization ($M_z$, the topological component from the modern orbital magnetization) by $\sigma_{xy}=-e\frac{\partial M_z}{\partial \mu}$. We reveal a microscopic mechanism to generate net orbital moment from the interplay of local crystal field and spin-orbit coupling for MnTe-type altermagnets, in which the magnetic anisotropy generates weak net magnetization without invoking exchange between neighboring spins (e.g., Dzyaloshinskii-Moriya interaction). Our work indicates that residual orbital and spin magnetization is an intrinsic thermodynamic property that governs anomalous transport in unconventional antiferromagnets, including altermagnets and noncollinear antiferromagnets.

Hydrogen transport through layered two-dimensional (2D) materials is central to technologies such as hydrogen storage, fuel cells, and isotope separation. Among these materials, MoS2 exhibits tunable interlayer diffusion properties, whose accurate theoretical description requires accounting for nuclear quantum effects (NQEs), including zero-point motion and tunneling. Here, we present a machine-learning-enhanced atomistic study of hydrogen and deuterium diffusion in layered MoS2 based on interatomic potentials trained on r2SCAN+rVV10 density-functional-theory data. Combining well-tempered metadynamics with path-integral molecular dynamics, we investigate diffusion across multiple MoS2 polytypes and twisted bilayer structures while explicitly incorporating NQEs. Our simulations show that NQEs substantially lower free-energy barriers for hydrogen diffusion at 300 K, significantly increasing the hydrogen self-diffusion coefficient compared to classical nuclei simulations. We further identify a pronounced kinetic isotope effect, with a 35 meV difference between hydrogen and deuterium quantum free-energy barriers. In twisted bilayer MoS2, hydrogen transport exhibits strong spatial variations governed by the local stacking environments within the moiré superlattices. These results highlight the critical role of NQEs in hydrogen transport through layered materials and provide atomistic insight intoisotope-selective diffusion in structurally complex 2D systems.