The combination of strong spin-orbit coupling and Coulomb interactions makes the $5d$ iridates a unique platform for realizing novel correlated electronic states. Here, utilizing infrared spectroscopy, we demonstrate that a robust Mott insulating state persists in the $1/3$-hole self-doped system ${\mathrm{La}}_3{\mathrm{Ir}}_3{\mathrm{O}}_{11}$, evidenced by the collapse of the Drude response and the emergence of sharp excitations across the Mott gap. Our theoretical calculations reveal that the insulating behavior arises from the cooperative interplay of structural distortions, spin-orbit coupling, and Coulomb interactions. Specifically, octahedral distortion and Ir-Ir dimerization split the $t_{2g}$ orbitals, driving the $J_{\mathrm{eff}}=1/2$ bands toward half filling while keeping the $J_{\mathrm{eff}}=3/2$ bands away from it. Consequently, electron correlations induce an orbital-selective Mott transition in the $J_{\mathrm{eff}}=1/2$ bands, whereas a band-insulating gap develops in the $J_{\mathrm{eff}}=3/2$ bands, thereby stabilizing the unconventional insulating state in ${\mathrm{La}}_3{\mathrm{Ir}}_3{\mathrm{O}}_{11}$. These findings provide new insights into the design and understanding of the insulating ground state of spin-orbit-coupled iridates.

We theoretically predict a spin-current analog of the quantized circular photogalvanic effect in Weyl semimetals. This phenomenon is forbidden in antiferromagnets by symmetry but uniquely allowed in altermagnets, highlighting a novel and intrinsic characteristic of altermagnetism. To systematically explore second-order spin current responses, we classify all symmetry-allowed responses based on spin point groups. Furthermore, we provide a comprehensive classification of altermagnetic Weyl semimetals by identifying spin space groups that host symmetry-enforced Weyl points. Utilizing this classification, we construct a symmetry-guided tight-binding model and confirm our predictions. Finally, we identify Weyl crossings in a material candidate via first-principle calculations. Our Letter unveils a distinctive optical response of altermagnets, paving the way for a new frontier in altermagnetism.

Néel vector, the order parameter of collinear antiferromagnets, serves as a state variable in associated antiferromagnetic (AFM) spintronic devices to encode information. A deterministic switching of Néel vector is crucial for the write-in operation, which, however, remains a challenging problem in AFM spintronics. Here we demonstrate, based on analytical derivation and macro-spin simulations, that Néel vector switching can be generally achieved via a current-induced spin torque, provided the spin accumulations responsible for this torque are non-identical between opposite sublattices. This condition occurs widely in AFM films, as symmetry equivalence between sublattice-dependent spin accumulations is usually absent, allowing unequal spin accumulations induced by Edelstein effect or a spin current. Unlike previously studied spin torques induced by uniform or staggered spin accumulations—where either the field-like or damping-like component dominates exclusively—the asymmetric spin torque features cooperative contributions from both components, leading to Néel vector dynamics that are fundamentally distinct from previous expectations. Crucially, the static states stabilized by the asymmetric spin torque enable versatile Néel vector switching strategies—field-free spin-transfer torque switching during current application, as well as field-free or field-assisted spin–orbit torque switching after the current pulse—demonstrating that established spin torque techniques from ferromagnetic spintronics can be directly adapted to AFM systems, a capability absent in previous theoretical frameworks. Our Letter establishes a general mechanism for current-induced Néel vector switching, which is in principle feasible for all collinear antiferromagnets, and thus paves the route to realize efficient writing in AFM spintronics.

Rhenium disulfide (${\mathrm{ReS}}_2$), a prototypical 2D semiconductor with an anisotropic ${1\mathrm{T}}^{\prime }$ structure due to the pronounced Peierls distortion, has demonstrated great potential for polarization-dependent optoelectronics and photonics. Here, we report an ultrafast phase transition occurring within 1 ps, accompanied by a one-dimensional Peierls-distortion relaxation in ${1\mathrm{T}}^{\prime }\text{−}{\mathrm{ReS}}_2$ revealed with combined 4D electron microscopy and time-dependent density functional theory calculations. Upon femtosecond laser pulse excitation, the Re-Re dimerization morphology rapidly transforms from a diamond cluster to zigzag chains and persists for several nanoseconds. This ultrafast Peierls-distortion relaxation is further verified by transient changes in optical anisotropy via polarization-dependent transient absorption spectroscopy. Time-dependent density functional theory calculations attribute this novel phase transition to strong correlation between Peierls distortion and impulsive photoexcited carrier doping, predicting a transient band-gap collapse. This Letter opens up an exciting avenue for ultrafast control of Peierls-distortion-induced anisotropy and the metal-insulator transition in ${1\mathrm{T}}^{\prime }\text{−}{\mathrm{ReS}}_2$.

We report Dirac–Landau polaritons observed by terahertz (THz) magnetoreflectivity spectroscopy, demonstrating strong coupling between cyclotron transitions of two-dimensional Dirac fermions in HgTe quantum wells and optical cavity modes. Under pulsed electrical injection we observe efficient nonlinear electroluminescence, with a strongly out-of-equilibrium polariton distribution dominated by emission from the upper polariton branches. Model analysis of the bias-dependent emission intensity and spectral narrowing indicates a polariton occupancy per mode approaching unity, with a possible contribution from stimulated polariton emission in the spectral region of the upper anticrossing. These results open prospects toward Dirac–Landau polariton condensates and low-threshold, tunable THz polariton lasers based on cyclotron emission.

We report the first direct experimental observation of the acoustic orbital Hall effect at metasurfaces using airborne vortex beams generated by a four-speaker source. Unlike traditional geometric or topological descriptions, we directly measure Hall-induced extrinsic orbital angular momentum (OAM) as a signature of twist-dependent Imbert-Fedorov shifts of the refracted beam. Through field decomposition, we reveal the coexistence of transverse energy flow and reconstructed axial angular-momentum symmetry, providing insight into extrinsic and intrinsic OAM in realistic systems beyond shift-based or topological arguments. In addition, we observe a geometric Hall effect in the tilted refracted beam. This Letter establishes a framework for measuring and interpreting acoustic Hall phenomena and advances emerging OAM-metasurface applications.

We uncover a chain of nonlinear modal interactions in softly clamped nanostring resonators. The process involves the sequential coupling of five mechanical modes, during frequency sweeps, yielding a broad nonlinear response with nearly constant amplitude. We demonstrate that soft clamping enables this cascaded energy transfer and amplifies the effective geometric nonlinearity of the driven mode by an order of magnitude. Analytical and finite element-based reduced-order models capture the key features of the coupling cascade and clarify its underlying mechanism. The phenomenon is generic in nonlinear vibrational systems and can be tailored through soft-clamping design strategies.

Various theoretical models predict the existence of extended $\gamma$-ray halos around normal galaxies that could be produced by interactions of cosmic rays with the circumgalactic medium or by annihilation or decay of hypothetical dark matter particles. Observations of M31, the closest massive galaxy, also corroborate this possibility. In this Letter, we describe our search for gamma-ray emission from the galaxies within 15 Mpc at energies higher than 2 GeV and try to assess its spatial extension. We use the latest catalog of local galaxies and apply a simple yet robust method of aperture photometry. By imposing the mass, energy, and spatial cuts, we selected a set of 16 late-type galaxies and found a statistically significant excess above the background level: a $p$ value of $3.7\times {10}^{-7}$ at $E>2\mathrm{GeV}$, reaching maximal significance of $p-\mathrm{val}=2.3\times {10}^{-8}$ for a subset of front-converted events with $E>2\mathrm{GeV}$, where the angular resolution is higher. More importantly, our analysis shows that this excess can be ascribed to an extended source with a radius $\sim 0.3°$ rather than a pointlike one. This, for $D=15\mathrm{Mpc}$, corresponds to a physical halo radius of $r_h=80\mathrm{kpc}$. In contrast, six early-type galaxies, which satisfied the same cuts, showed no excess. Our results are supported by the stacking likelihood analysis technique, which significantly ($5.6\sigma$) detected an extended excess. The difference between the late- and early-type galaxies and a rather irregular shape of the extended source that we found, indicate that this high-energy emission is more likely caused by the interactions of cosmic rays with the circumgalactic medium, in preference to dark matter annihilation and decay processes.

Gravity and gauge theory are concretely linked by the double copy. Although well-studied at the level of perturbative scattering in vacuum, far less is known about nonperturbative aspects or extensions of double copy beyond trivial backgrounds. We show here how Hawking radiation in a collapse metric, its associated thermal spectrum, and horizon dependence, emerges from the double copy of particle production in a background gauge field, where there is no global horizon or thermal spectrum. Our approach combines worldline and amplitude methods, and allows the unification of several classical and quantum double copy prescriptions for black hole spacetimes.

The Hawking radiation spectrum from a collapsing null shell can be derived via the double copy of a simpler gauge theory calculation. Analyzing the non-Abelian Yang-Mills root of this process, we demonstrate that the radiation spectrum is thermal in the color charge eigenvalue $\lambda$, not energy. Considering the $\mathrm{SU}(N_c)$ gauge theory in the large $N_c$ limit, we find the differential spectrum $\mathrm{d}N/\mathrm{d}\lambda$ is a product of the gravitationally familiar Planck-like factor and the color phase space density, modeled here as the Wigner semicircle from random matrix theory. This reveals that apparent energy thermality in gravity is the direct dual of charge thermality in its underlying non-abelian gauge theory.

The initial-state geometry in relativistic heavy-ion collisions provides a novel probe to nuclear cluster structure. For ${}^{20}\mathrm{Ne}$, a novel approach is proposed to distinguish between the cluster configurations ($5\alpha$ versus $\alpha +{}^{16}\mathrm{O}$) in order to gain insight into nuclear structure transitions governed by many-body quantum correlations. Through analytical calculations with the microscopic Brink model and event-by-event simulations using the hydrodynamic framework, we establish the normalized symmetric cumulant NSC(3, 2) and the Pearson coefficient ${\rho }_2(v_2^2,\delta [p_{\mathrm{T}}])$ as quantitative discriminators to reveal enhanced cluster degrees of freedom in the ground state of ${}^{20}\mathrm{Ne}$. The ultracentral $\mathrm{Ne}+\mathrm{Ne}$ collisions at the LHC can experimentally identify these two competing configurations via these flow correlation observables, opening a new paradigm for probing clustering in light nuclei.

We present a quantum logic scheme mitigating systematic effects in the measurement of magnetic properties of ions caused by temporal magnetic field fluctuations through comagnetometry. This is achieved through simultaneous interrogation of a spectroscopy ion and a cotrapped reference ion with a precisely known $g$ factor confined in a Paul trap. This allows measurement of the ground state $g$ factors of a single ${}^{48}{\mathrm{Ti}}^{+}$ ion with uncertainties at the ${10}^{-6}$ level in the weak $B$-field regime. The experimental scheme can be applied to many ions, including those that cannot be directly laser cooled. We compare the experimentally determined $g$ factors of ${}^{48}{\mathrm{Ti}}^{+}$ with new theoretical predictions using a combination of configuration interaction and second-order many-body perturbation theory. Theory and experiment agree within the expected level of accuracy.

Pauli crystals are unique geometric structures of noninteracting fermions, resembling crystals, that emerge solely from Fermi statistics and confinement. Unlike genuine quantum crystals that arise from interparticle interactions, Pauli crystals do not break translation symmetry but nonetheless exhibit nontrivial many-body correlations. In this Letter, we explore Pauli crystal formation in a cavity-fermion setup. We analytically show that when coupled to a cavity, degeneracy in Pauli crystals can trigger zero-threshold transitions to superradiance. This superradiance is accompanied by the emergence of a genuine quantum crystalline state, wherein the atomic density is periodically modulated. We substantiate our findings using state-of-the-art numerical simulations. The combined interplay between statistics, confinement geometry, and interactions mediated by light thus facilitates a novel pathway to quantum crystallization.

Using particle-in-cell simulations that label ions and electrons according to their initial inflow region, we find that during 2D collisionless magnetic reconnection, the bulk flow of the plasma from each inflow side crosses paths with plasma from the other inflow side and crosses the midplane before being redirected into an outflow jet. This feature, which we term “flow crossover,” implies mechanisms to generate bulk motion in a direction parallel to the magnetic field. We find that ions and electrons undergo different parallel driving mechanisms, leading to different flow crossover patterns. The parallel bulk flow for ions is generated more locally within the ion diffusion region, whereas the parallel bulk flow for electrons is mostly generated outside the electron diffusion region. Consequently, the reconnection outflows are more of a parallel flow than a perpendicular flow, especially for the electron outflow. The flow crossover and the parallel outflow patterns occur not only in symmetric reconnection but also in the more complex scenario of a guide-field asymmetric reconnection, suggesting that it is a general feature of collisionless magnetic reconnection. Because the plasma outflow on one side of the midplane mostly originates from the inflow plasma on the other side, we predict that near an asymmetric reconnection site in a collisionless space plasma, in situ observations across the outflow region could reveal locally reversed gradients in plasma properties. These results are potentially important for quantifying transport across the dayside magnetopause of Earth and other planets and the energy partition in reconnection, including electron and ion heating.

Atomic force microscopy is used to analyze the temperature dependence of nanoscale wear occurring during reciprocal line scanning of a ${\mathrm{SiO}}_2$ surface using diamond atomic force microscopy tips. Unexpectedly, our experiments show a wear rate that decreases with temperature. Thereby, the results cannot readily be reconciled with the common model of atomic scale wear, which assumes an abrasive process of thermally activated and shear-assisted atom-by-atom removal. Instead, shear-assisted tribochemical processes are taken into account. This is done based on a multibond model for single-asperity tribochemical wear as well as recent analysis of contact aging driven by bond formation for silica and diamond systems. We consider how thermally activated bond formation at different temperatures is met by temperature-dependent probabilities for bond rupture accompanied by wear. This allows us to rationalize the experimental results and link the temperature dependence of wear to the way an increasing number of interfacial bonds are ruptured at lower temperatures. Ultimately, our experiments thereby expand the emerging multibond model of single-asperity nanofriction and tribochemical wear to the temperature domain.

We report magnetic bistability in single Dy atoms on NaCl(100) thin films. Individual Dy atoms substituting Na at the surface of the NaCl layer are thermally stable up to at least 300 K, display $4f^9$ occupancy, out-of-plane easy magnetization axis, and long spin relaxation time $T_1$ of about 10 s at 2.5 K; therefore, they are the first single-atom magnet on a thermally stable adsorption site. Dy atoms adsorbed onto the Cl and bridge sites display $4f^{10}$ occupancy. Dy on top-Cl exhibit magnetic hysteresis and a $T_1$ of 550 s at 0.3 T and 2.5 K. The observed slow magnetic relaxation of Dy on both adsorption sites introduces NaCl as an effective platform for single-atom magnets.