The chromium spinels ${\mathrm{MgCr}}_2{\mathrm{O}}_4$ and ${\mathrm{ZnCr}}_2{\mathrm{O}}_4$ are prime examples of the highly frustrated pyrochlore lattice antiferromagnet. Experiment has carefully established that both materials, upon cooling, distort to lower symmetry and order magnetically. We study the nature of this process by a combination of density-functional-theory–based energy mapping and classical Monte Carlo simulations. We first computationally establish precise Heisenberg Hamiltonian parameters for the high temperature cubic and the low temperature tetragonal and orthorhombic structures of both spinels. We then investigate the respective ordering temperatures of high symmetry and low symmetry structures. We carefully compare our results with experimental facts and find that our simulations are remarkably consistent with a type of spin-Peierls mechanism, adapted to three dimensions, where the structural distortion is mediated by a magnetic energy gain due to a lower degree of frustration.

We determine the asymptotic relaxation rate of a Brownian particle in a harmonic potential perturbed by quenched Gaussian disorder, a simplified model for rugged energy landscapes in complex systems. Depending on the properties of the disorder, we show that the mean and variance of the asymptotic relaxation rate are nonmonotonous functions of the parameters for a broad class of disorders. In particular, the rate of relaxation may either increase or decrease exponentially compared to the unperturbed case. This implies that disorder may, depending on its properties, both significantly speed up and slow down relaxation. In the limit of weak disorder, we derive the probability distribution of the asymptotic relaxation rate and show that it is Gaussian, with analytic expressions for the mean and variance that feature universal limits. Our findings indicate that controlled disorder may serve to tune the relaxation speed in complex systems.

We report the first experimental demonstration of the odd-cycle game. We entangle two atoms separated by $\sim 2\mathrm{m}$, and the players use them to win the odd-cycle game with a probability $\sim 26\sigma$ above that allowed by the best classical strategy. The experiment implements the optimal quantum strategy, is free of loopholes, and achieves 97.8(3)% of the theoretical limit to the quantum winning probability. We perform the associated Bell test and measure a nonlocal content of 0.54(2)—the largest value for physically separate devices, free of the detection loophole, ever observed.

Supernova theory has struggled to explain the lightest known neutron star candidate with an accurate mass determination, the $1.174M_{\odot }$ companion in the eccentric compact binary system $\mathrm{J}0453+1559$. To improve the theoretical lower limit for neutron star birth masses, we perform 3D supernova simulations for five stellar models close to the minimum mass for iron core collapse. We obtain a record-low neutron star mass of $1.192M_{\odot }$ and a substantial kick of $\sim 100\mathrm{km}{\mathrm{s}}^{-1}$. Given residual uncertainties in stellar evolution, a neutron star origin for the $1.174M_{\odot }$ object remains plausible.

We define a general strategy for finding new heavy-fermionic materials without rare-earth elements: doping a Hund metal with pronounced orbital-selective correlations towards half-filling. We argue that in general band structures, a possible orbital-selective Mott transition is frustrated by interorbital hopping into heavy-fermion behavior—where $d$ orbitals provide both the heavy and the light electrons—which is enhanced when approaching half-filling. This phase ultimately disappears due to magnetic correlations, as in a standard Doniach diagram. Experimentally we have hole doped ${\mathrm{CsFe}}_2{\mathrm{As}}_2$, a Hund metal with 0.5 electrons/Fe away from half-filling, and obtained a heavy fermionic state with the highest Sommerfeld coefficient for Fe pnictides to date ($270\mathrm{mJ}/\mathrm{mol}{\mathrm{K}}^2$), before signatures of an antiferromagnetic phase set in.

${\mathrm{MoTe}}_2$ monolayers and bilayers are unique within the family of van der Waals materials since they pave the way toward atomically thin infrared light-matter quantum interfaces, potentially reaching the important telecommunication windows. Here, we report emergent exciton polaritons based on ${\mathrm{MoTe}}_2$ monolayers and bilayers in a low-temperature open microcavity in a joint experiment-theory study. Our experiments clearly evidence both the enhanced oscillator strength and enhanced luminescence of ${\mathrm{MoTe}}_2$ bilayers, signified by a 38% increase of the Rabi splitting and a strongly enhanced relaxation of polaritons to low-energy states. The latter is distinct from polaritons in ${\mathrm{MoTe}}_2$ monolayers, which feature a bottlenecklike relaxation inhibition. Both the polaritonic spin valley locking in monolayers and the spin-layer locking in bilayers are revealed via the Zeeman effect, which we map and control via the light-matter composition of our polaritonic resonances.

Single-spin asymmetries observed in polarized deep-inelastic scattering are important probes of hadron structure. The Sivers asymmetry has been the focus of much attention in QCD phenomenology and is yet to be understood at the quark level. In this Letter, we present a lattice QCD calculation of the spatial distribution of a color-Lorentz force acting on the struck quark in a proton. We determine a spin-independent confining force, as well as spin-dependent force distributions with local forces on the order of $3\mathrm{GeV}/\mathrm{fm}$. These distributions offer a complementary picture of the Sivers asymmetry in transversely polarized deep-inelastic scattering.

Under the widely accepted but unproven assumption that the one-dimensional $S=1$ antiferromagnetic Heisenberg model has a unique gapped ground state, we prove that the model belongs to a nontrivial symmetry-protected topological phase. In other words, we rigorously rule out the possibility that the model has a unique gapped ground state that is topologically trivial. To be precise, we assume that the models on open finite chains with a boundary magnetic field have unique ground states with a uniform gap and prove that the ground state of the infinite chain has a nontrivial topological index. This further implies the presence of a gapless edge excitation in the model on the half-infinite chain and the existence of a topological phase transition in the model that interpolates between the Heisenberg chain and the trivial model.

Dark matter particles with a mass around 1 eV can decay into near-infrared photons. Utilizing available public blank sky observations from the NIRSpec IFU on the James Webb Space Telescope (JWST), we search for a narrow emission line due to decaying dark matter and derive leading constraints in the mass range 0.8–3 eV on the decay rate to photons, and more specifically, on the axion-photon coupling for the case of axionlike particles. We exclude $\tau <3.5\times {10}^{26}\mathrm{s}$ at $m_{\mathrm{DM}}\simeq 0.8\mathrm{eV}$ and, in the case of axions, $g_{a\gamma \gamma }>1.3\times {10}^{-11}{\mathrm{GeV}}^{-1}$ for $m_a\simeq 2.2\mathrm{eV}$. Our results do not rely on dedicated observations, rather we use blank sky observations intended for sky subtraction, and thus our reach may be automatically strengthened as JWST continues to observe.

The recently launched James Webb Space Telescope can resolve eV-scale emission lines arising from dark matter decay. We forecast the end-of-mission sensitivity to the decay of axions, a leading dark matter candidate, in the Milky Way using the blank-sky observations expected during standard operations. Searching for unassociated emission lines will constrain axions in the mass range 0.18 to 2.6 eV with axion-photon couplings $g_{a\gamma \gamma }\gtrsim 5.5\times {10}^{-12}{\mathrm{GeV}}^{-1}$. In particular, these results will constrain nucleophobic QCD axions to masses $\lesssim 0.2\mathrm{eV}$.

Can complex classical systems be designed to exhibit superpositions of tensor products of basis states, thereby mimicking quantum states? We exhibit a one-to-one map between the product basis of quantum states comprising an arbitrary number of qubits and the eigenstates of a construction comprising classical oscillator networks. Specifically, we prove the existence of this map based on Cartesian products of graphs, where the graphs depict the layout of oscillator networks. We show how quantumlike gates can act on the classical networks to allow quantumlike operations in the state space.

We report a combined electrical transport and optical study of the superconductivity in atomically thin ${\mathrm{NbSe}}_2$. When subjected to an out-of-plane magnetic field, an anomalous metallic state emerges, characterized by a finite longitudinal resistance and a vanishing Hall resistance, suggesting the presence of particle-hole symmetry. We establish a superconducting Higgs mode in atomically thin samples, which reveals enduring superconducting fluctuations that withstand unexpectedly high reduced magnetic fields. These findings provide evidence of robust locally paired electrons in the anomalous metallic state, affirming its bosonic nature.

An important route of engineering topological states and excitations is to combine superconductors (SC) with the quantum Hall (QH) effect, and over the past decade, significant progress has been made in this direction. While typical measurements of these states focus on electronic properties, little attention has been paid to the accompanying thermal responses. Here, we examine the thermal properties of the interface between type-II superconducting electrodes and graphene in the QH regime. We use the thermal noise measurement to probe the local electron temperature of the superconductor next to the biased interface. Surprisingly, the measured temperature rise indicates that the superconductor provides a significant thermal conductivity, which is linear in temperature. This suggests electronic heat transport and may be unexpected, because the number of the quasiparticles in the superconductor should be exponentially suppressed. Instead, we attribute the measured electronic heat conductivity to the overlap of the normal states in the vortex cores.

Defect physics is at the heart of microelectronics. By keeping track of the reference energy in total energy calculations, we explicitly show that the “potential alignment” correction vanishes, and the classic Makov-Payne correction yields accurate results. From linear response theory, we further formulate an accurate expression for the quadrupole correction. Application to numerous defects including anisotropic material yields accurate formation energies in small supercells, and the historically slow convergence of the $2+$ diamond vacancy is shown to be a result of slow varying gap levels of the defect leading to a size-dependent dielectric constant.

The highly excited electron-hole plasma (EHP) phase is a natural platform for studying amplified spontaneous emission (ASE), yet research into the many-body physics of EHP and ASE in two-dimensional (2D) semiconductors remains limited. Here, we report the first observation of ASE from EHP in 2D semiconductors, evidenced by an unusually sharp enhancement of emissions in suspended bilayer ${\mathrm{WS}}_2$ at a threshold power, confirming the transient differential transmission measurements under continuous wave excitations. We modeled the optical dielectric response of varying densities of excited carriers and accurately reproduced the observed emission features across different electron-hole phases from bilayer ${\mathrm{WS}}_2$ over a simple Fabry-Pérot cavity. This, together with spatially resolved emissions, confirmed that ASE stems from the degenerate EHP. Our analysis highlights the crucial role of many-body interactions in achieving ASE in 2D EHP. This Letter provides a new insight into the rich physics in EHP and expands the potential for developing advanced 2D semiconductor based optoelectronic devices.

The presence of disorder can severely impede wave transport, resulting in the famous Anderson localization. Previous theoretical studies found that Anderson transition can exist in one-dimensional (1D) non-Hermitian disordered rings with chiral hopping, defying the scaling theory of localization for Hermitian systems. In these systems, localized (extended) modes are associated with real (complex) energies. Here, we report that Anderson localized modes with complex energies can also exist in such systems. The emergence of the complex-energy localized modes (CELMs) directly ties to the properties of the corresponding pristine non-Hermitian system. Specifically, the density of states of the complex spectrum under the periodic boundary condition and the non-Bloch parity-time transition of the open-boundary chain both play critical roles in the emergence of the CELMs. The coexistence of extended modes, real-energy localized modes (RELMs), and CELMs should be a generic phenomenon for 1D non-Hermitian disordered systems under class AI. Our work shows that the interplay between Anderson mechanism and non-Hermitian physics enriches the properties of disordered media and opens new possibilities for controlling wave transport.

We show that driving optical phonons above a threshold fluence induces spatiotemporal orders, where material properties oscillate at an incommensurate wave vector $q_0$ in space and at half the drive frequency in time. The order is robust against temperature on timescales much larger than the lifetime of the excited modes and can be accompanied by a static $2q_0$ modulation. We make predictions for time-resolved diffraction and provide estimates for candidate materials. Our results show the possibility of using THz waves in solids to realize tunable incommensurate orders on the nanoscale.

Multiterminal Josephson circuits have been proposed as a promising platform to host synthetic topological phases of matter, Floquet states, and multiplet supercurrents that are mediated by pairs of Cooper pairs. Here, we explore a Josephson circuit in which three superconducting electrodes are connected through Josephson junctions to a common superconducting island. We demonstrate the dynamic generation of the multiplet supercurrents, which are found to be robust to elevated temperatures and are confirmed by exhibiting the expected Shapiro step quantization under a microwave drive. We also find an unexpected novel supercurrent, which couples a pair of contacts that are both voltage-biased with respect to the common superconducting island. We show that this supercurrent also results from synchronization of the phase dynamics of the device, opening pathways to study the interplay of nonlinear, quantum, and topological physics.

We demonstrate the existence of topological phase transitions in interacting, symmetry-protected quantum matter at finite temperatures. Using a combined numerical and analytical approach, we study a one-dimensional Su-Schrieffer-Heeger model with added Hubbard interactions, where no thermodynamic phase transition occurs at finite temperatures. The transition is signalled by a quantized, nonlocal bulk topological order parameter. It is driven by defects, which are enabled by the combination of interaction and thermal activation, with no counterpart in the noninteracting limit. The defects localize topological zero modes, which, when sufficiently abundant, cause the order parameter to vanish. This phenomenon, interpreted via bulk-boundary correspondence, reflects the loss of a topological edge mode at a well-defined critical temperature in the thermodynamic limit. Unlike zero-temperature topological transitions, these finite-temperature transitions lack thermodynamic signatures but remain observable in controlled quantum systems, such as ultracold fermionic atoms in optical lattices.

Condensation of exciton polaritons has been recently observed in gap-confined states of one-dimensional photonic crystal waveguides. Here we focus on the theoretical emergence of a second emission threshold in this platform, in addition to the one associated with condensation at zero momentum, due to the nonlinear polariton scattering from the condensate into finite momentum eigenmodes. The physics of this spatially modulated condensate is related to a spontaneous breaking of both phase and translational symmetries simultaneously, bearing similarities with the highly sought supersolid phase in Helium and ultracold atomic gases but with a novel mechanism typical of the driven-dissipative scenario. We then propose clear-cut and unequivocal experimental signatures that would allow to identify such non-equilibrium supersolidity of polariton condensates.