Twisted ${\mathrm{MoTe}}_2$ hosts intriguing correlated quantum phenomena including the fractional quantum anomalous Hall effect in twisted bilayer (t-BL) ${\mathrm{MoTe}}_2$ near 3.7°, which is sensitive to the twist angle and moiré superlattices. Here, we directly visualize the twist-angle-modulated electronic structure of t-BL and twisted double-bilayer (t-DBL) ${\mathrm{MoTe}}_2$ near this critical angle. We find that the moiré superlattice not only modifies the relative energy between the $\mathrm{\Gamma }$ and $K$ valleys in t-BL ${\mathrm{MoTe}}_2$, but also strongly reconstructs the $\mathrm{\Gamma }$ valley for both t-BL and t-DBL ${\mathrm{MoTe}}_2$. Specifically, the deep $p_z$-derived band at $\mathrm{\Gamma }$ exhibits a distinct splitting that systematically varies with increasing twist angle. Theoretical analysis suggests that this modulation arises from the twist-angle-dependent lattice relaxation, especially interfacial corrugations. Our work directly visualizes the moiré-modulated electronic structure and provides key spectroscopic information of lattice relaxation and interlayer interactions underlying the physics of twisted ${\mathrm{MoTe}}_2$.

Disorder-induced localization of electrons and electron-electron interaction are among the most fundamental problems in condensed matter physics. In two-dimensional electron systems, extensive studies have led to the emergence of a scaling picture, characterized by a set of universal critical exponents that govern the transitions between the integer quantum Hall plateaus. From the temperature dependence of the plateau-to-plateau transitions, experiments primarily report $\kappa \simeq 0.42$, implying a dynamic exponent $z=1$, consistent with a theoretical picture where electrons have a long-range ($1/r$) interaction. Theory also predicts that $z=2$ for short-range electron interaction, but an experimental verification has remained elusive. Here, we directly probe the influence of Coulomb interaction on these transitions using a bilayer electron system confined to a GaAs double quantum well device. The two layers are in close proximity, with an interlayer distance approximately equal to the magnetic length at the relevant magnetic fields. By tuning the electron density in the top layer, we access both insulating and metallic phases of the electrons in this layer as a function of magnetic field, allowing in situ control of the unscreened and screened interaction strengths in the bottom layer as it goes through its plateau-to-plateau transitions. In the unscreened case, we measure $\kappa \simeq 0.42$ consistent with the widely reported value. More importantly, when screening is introduced, $\kappa$ is reduced to $\simeq 0.22$, implying $z=2$. Our results provide direct experimental evidence for the role of electron-electron interaction in determining critical behavior in the quantum Hall regime, and demonstrate screening as a powerful tuning parameter for engineering quantum criticality.

Topological materials host exotic phenomena rooted in their distinctive band topology, where band splitting plays a central role in spin transport and nonlinear optical responses. Terahertz (THz) emission spectroscopy provides a time-resolved probe of carrier dynamics governed by band splitting. In ferromagnet-topological material heterostructures, THz emission is typically attributed to spin-to-charge conversion (SCC). However, emerging experimental observations indicate that the SCC mechanism alone cannot fully account for the dominant origin of THz emission in certain systems, the potential contribution of band splitting in topological materials remaining unexplored. Here, we demonstrate that ${\mathrm{PtTe}}_2/{\mathrm{Cr}}_5{\mathrm{Te}}_6$ heterostructures exhibit enhanced, field-free THz emission that is not driven by SCC, but by the circular photogalvanic effect (CPGE). Supported by the control experiments and first-principles calculations, we show that band engineering at the heterointerface is essential for CPGE-driven ultrafast photocurrents. Remarkably, the polarity of the emitted THz wave can be reversibly and deterministically switched by the laser helicity without altering the magnetic field. These findings highlight the photogalvanic effect as a powerful and versatile origin of THz generation in spintronic heterostructures. Our Letter paves a pathway toward all-optical, helicity-controlled ultrafast THz sources and spin-optoelectronic devices based on quantum materials.

Nonreciprocal interactions in active matter give rise to a multitude of fascinating phenomena among which are collective oscillatory states without intrinsic particle chirality and active turbulence. Here we show that, in a paradigmatic model for nonreciprocal flocking, the two-species Vicsek model, these two states coexist: chiral order for small flocks and extensive spatiotemporal chaos for large flocks, both separated by a finite-wavelength instability whose scale is set by the rotation radius of the chiral orbits. For system sizes larger than this length scale extensive spatiotemporal chaos unfolds, as manifested by an extensive number of positive Lyapunov exponents as well as of Floquet exponents, a finite correlation and chaotic length, and a broad energy spectrum. Our results suggest that complex, turbulent behavior is a generic possibility in systems where particles or fields interact asymmetrically and may have significant implications for understanding how nonreciprocal interactions could drive chaotic, fluidlike behavior in active matter.

We show that chiral order in two-dimensional nonreciprocal flocking mixtures is generically unstable. Combining large-scale agent-based simulations with a coarse-grained continuum description, we demonstrate that rotating chiral states emerging from antisymmetric couplings are destroyed by the proliferation of topological defects. The resulting dynamics is spatiotemporally chaotic and characterized by a finite correlation length that diverges as nonreciprocity vanishes. On length scales below this cutoff, density and orientational order fluctuations remain scale-free, but the associated scaling exhibits nonuniversal exponents. We attribute this atypical behavior to the coupling between density and order, which causes topological defects to act as persistent sources of nonlinear fluctuations.

Solar coronal mass ejections (CMEs) are routinely observed, but as of yet there exist few convincing detections of stellar CMEs. A reason for this could be that the stronger magnetic fields of these stars, compared to that of our Sun, would prevent CME to form and escape. Here we combined astrophysical simulations, measurements of scaled high-energy laser-driven plasma flows, and 3D magnetohydrodynamic modeling to test this hypothesis. Simulations show that, in a 100 G stellar dipole field, low-plasma $\beta$ CMEs become magnetically confined. In the laboratory, a laser-produced plasma stream scaled to stellar CME conditions propagates freely at low applied magnetic fields (approximately 30 G stellar equivalent), but becomes unstable and halts entirely when the field is increased to $3\times {10}^5\mathrm{G}$ (i.e., a 100 G equivalent). Analytical estimates and numerical simulations suggest that the sudden disruption of the flow is induced by a kink instability. Even though the laboratory environment does not fully reproduce the complex magnetic flux-rope topology of CMEs, these results provide the first laboratory-scale evidence that strong stellar magnetic fields can fully suppress CME propagation, offering a physical explanation for their lack in stellar observations and highlighting the role of magnetic confinement in stellar evolution and exoplanet space weather.

We present the thermopower of ${\mathrm{EuCd}}_2{\mathrm{P}}_2$, a material which exhibits a large resistivity peak with significant magnetic field dependence in the temperature range of 10–25 K. In the same region, we observe a highly unusual behavior of the thermopower with two sign changes and giant extrema. The overall variation of the thermopower exceeds $4000\mathrm{\mu }\mathrm{V}/\mathrm{K}$ and takes place in an extremely narrow temperature region of less than 5 K. The anomaly is suppressed completely in a small magnetic field of 0.5 T. We discuss this observation using a simple drift-diffusion picture and taking into account that the temperature gradient inducing the thermopower voltage is accompanied by a gradient of the electrical resistivity. Our simple estimation yields the correct magnitude, shape, and field dependence of the thermopower anomaly observed in ${\mathrm{EuCd}}_2{\mathrm{P}}_2$. These results open a new route to giant thermopower values via gradients of electronic properties.

A search for Higgs boson ($H$) production in association with two vector bosons ($V=W$, $Z$) via vector-boson scattering (VBS) is presented using proton-proton collision data collected at $\sqrt{s}=13\mathrm{TeV}$ by the CMS experiment, corresponding to an integrated luminosity of $138{\mathrm{fb}}^{-1}$. Events containing two forward jets consistent with VBS, a large-radius jet from the decay of a boosted $H$ to a pair of $b$ quarks, and zero, one, or two charged leptons coming from $V$ decays are selected. The process is excluded at 95% confidence level for observed (expected) values of the $VVHH$ coupling modifier ${\kappa }_{2V}$ outside the interval $0.40<{\kappa }_{2V}<1.60$ ($0.34<{\kappa }_{2V}<1.66$), assuming standard model values for all other couplings, thus establishing a novel probe of the $VVHH$ interaction. Constraints are also set on the individual ${\kappa }_{2W}$ and ${\kappa }_{2Z}$ coupling modifiers and on the allowed region in the ${\kappa }_{2W}\text{−}{\kappa }_{2Z}$ plane.

Diamond offers an exceptional platform for optoelectronics owing to its ultra-wide band gap, superior thermal and photonic properties. Yet its optical response is notoriously difficult to tune, as conventional doping suffers from deep impurity levels and poor activation efficiency. Here, we show that strain-gradient engineering provides a doping-free route to modulate broadband optical emission in microfabricated diamond. By taking advantage of size-induced large elasticity, we show that controlled elastic bending of diamond nanoribbons generates spatially varying strain fields that can be resolved at nanoscale using STEM-EELS, which reveals synchronous electronic bandgap shifts and phonon spectrum broadening. Spatially mapped cathodoluminescence exhibits continuous emission shifts, accompanied by intensity variations and spectral widening. Theoretical analyses show that nonuniform strain couples electronic band restructuring with phonon mode redistribution, expanding the pathways for phonon-assisted optical transitions. These findings transform diamond from a static wide-band-gap semiconductor into a mechanically reconfigurable broadband emitter, establishing strain-gradient engineering as a general paradigm for tunable photonics in wide-band-gap semiconductors.

The Eu valence in EuO under compression has been debated since the first observation of a pressure-induced isostructural volume collapse by Jayaraman five decades ago. Spectroscopic studies at the Eu $L_3$ edge suggested a valence change from divalent to trivalent due to promotion of charge from the half-filled $4f$ shell to empty $5d$ states, while density functional theory investigations have reported both support for and against such a valence change. The Eu $N_{4,5}$ edges ($4d\to 4f$ excitations) are highly sensitive to the $4f$ occupancy and thus to the Eu valence. Using x-ray Raman scattering, we measure the Eu $N_{4,5}$ edges of EuO up to 66 GPa and observe no significant change in spectral shape indicative of a modification of the $4f$ occupation. Our results therefore support a robust ${\mathrm{Eu}}^{2+}$ state across the isostructural transition at 35 GPa and the subsequent B1–B2 transition at 44 GPa.

Here, we address the fundamental question of whether an idealized system of $N$ atoms will show collective behavior and superradiance when it emits fermions instead of photons. We show that for single-fermion emission processes, the maximum emission is $\propto N$ and not $\propto N^2$, which proves the absence of superradiance and shows that the recent proposal to realize a superradiant neutrino laser is impossible. This can be understood as either destructive interference of fermionic transition amplitudes, or Pauli blockade by collective excitations with fermionic nature. We derive the exact solution of the fermionic Dicke problem and analyze the decay dynamics in various regimes. We extend the proof to arbitrary Hamiltonians and show that the jump rate operator for neutrino emission has a maximum eigenvalue of $N$ times the single-particle rate ${\mathrm{\Gamma }}_0$. States with low excitation can show collective behavior and emit at a rate of $N{\mathrm{\Gamma }}_0$.

This Letter lays out the principles of how Bose-Einstein condensates can modify radioactive decay. We highlight the challenges of many modes and short coherence times due to the $\approx \mathrm{MeV}$ energies of the emitted radiation. Recent proposals for gamma-ray and neutrino lasers claim that using a Bose-Einstein condensate as a source would solve these issues. We show that this is not the case, and the proposed experiments would have a gain of only ${10}^{-16}$ or smaller. We also analyze proposals for gamma-ray lasers based on stimulated annihilation of positronium Bose-Einstein condensates.

${\mathrm{Ta}}_2{\mathrm{NiSe}}_5$ continues to be investigated for its phase transition at $T_{\mathrm{c}}=326\mathrm{K}$, where it develops both an electronic gap and a distortion of its $\mathrm{Ta}/\mathrm{Ni}$ chains. One intriguing feature at $T_{\mathrm{c}}$ seen in thermal transport is the giant anisotropic scattering of phonons moving perpendicular to the chains, which is apparently associated with the softening of a transverse acoustic phonon, but whose microscopic origin and significance demand clarification. By tuning the normal-state band overlap or gap with S substitution, we uncover a close connection between this soft-phonon transport anomaly and underlying electronic instabilities: when ${\mathrm{Ta}}_2\mathrm{Ni}({\mathrm{S}}_x{\mathrm{Se}}_{1-x}{)}_5$ approaches a band insulator at high $x$, and signatures of the electronic transition are suppressed, the soft-phonon transport anomaly concomitantly vanishes. Our results establish the following picture for the ${\mathrm{Ta}}_2\mathrm{Ni}({\mathrm{S}}_x{\mathrm{Se}}_{1-x}{)}_5$ family: near the S end, a sole lattice instability gives rise to a weak structural transition with $T_{\mathrm{c}}$ approaching 130 K. Near the Se end, additional electronic instabilities boost $T_{\mathrm{c}}$ up to 326 K and amplify experimental signatures of the transition. The strong interaction between electrons, holes, and the lattice is manifested as a soft-phonon transport anomaly accompanied by electronic fluctuations, which include excitonic and hybridization-gap fluctuations.

Gauge theories form a large class of interacting conformal field theories in 3D, among which critical Chern-Simons-matter theories play a prominent role. Here, we study a simple instance: a gapless complex scalar coupled to a $\mathrm{U}(1{)}_2$ Chern-Simons gauge field. This theory is conjectured to be dual to three other Chern-Simons-matter theories and to describe the transition between a Kalmeyer-Laughlin chiral spin liquid (a $\nu =1/2$ bosonic Laughlin state) and a trivially gapped phase. Using the fuzzy-sphere regularization, we realize the corresponding quantum phase transition between a ${\nu }_f=2$ fermionic integer quantum Hall state and a ${\nu }_b=1/2$ bosonic fractional quantum Hall state. We show that the transition is continuous and governed by a conformal field theory with $SO(3)$ global symmetry. The operator spectrum contains only one relevant Lorentz scalar, the SO(3) singlet with scaling dimension ${\mathrm{\Delta }}_S=1.52(18)$, which tunes the transition. Our nonperturbative results identify the universality class naturally associated with the $\mathrm{U}(1{)}_2$ Chern-Simons-Higgs theory and show that the conjectured dualities remain self-consistent.

Near-field enhancement in nanocavities governs the efficiency of nonlinear optical processes and ultrafast light-matter interactions. However, maximizing the cavity quality factor does not necessarily maximize the response under femtosecond excitation. Here, we experimentally demonstrate that hybrid metal-dielectric metasurfaces provide a practical platform for optimizing this trade-off. By coupling a low-Q localized surface plasmon resonance of Au nanodisks to a high-Q dielectric mode of a ${\mathrm{TiO}}_2$ metasurface, we continuously tune the Q factors of the hybrid modes over a broad range while preserving the plasmonic hotspot geometry. Using four-photon photoemission electron microscopy under 100-fs excitation, we map the nonlinear near-field response and correlate it with spectrally extracted Q factors and ultrafast dynamics measured by time-resolved photoemission electron microscopy. The response varies nonmonotonically with Q and reaches a maximum at $\mathrm{Q}\approx 20$, where the photoemission yield is enhanced approximately 15-fold relative to the uncoupled metasurface. These results identify pulse-cavity Q-factor matching between the cavity and the driving pulse as a key design principle for pulsed-laser nanophotonics.

Why do nonaxisymmetric stellarators avoid ballooning crashes that afflict tokamaks? Three-dimensional geometry induces Anderson localization of ballooning modes, converting a global instability into a Ginzburg-Landau network of isolated wave packets. Global stability reduces to a percolation problem: Below a critical threshold, instability is arrested; above it, a crash occurs. This explains benign stellarator saturation, predicts vulnerability in quasisymmetric designs, and introduces the critical threshold as a nonlinear stability metric for reactor optimization, pending experimental validation.

We present a rigorous derivation of the orbital magnetization for interacting electrons within the self-consistent Hartree-Fock approximation. Our method also allows us to derive formulas for the orbital magnetic susceptibility. The results are expressed entirely in terms of the self-consistent wave functions and the Hartree-Fock energy spectrum at zero magnetic field. We find that the formula for the orbital magnetization is the same as in the noninteracting case, provided that the Hamiltonian and Bloch wave functions are replaced by their Hartree-Fock counterparts. By contrast, the orbital magnetic susceptibility contains an additional interaction-induced contribution that cannot be obtained by such a replacement. We test the formulas on an interacting Rashba model, finding an agreement with calculations performed at a small but nonzero external magnetic field.

In the absence of spin-orbit coupling, collinear magnets are classified as even-wave magnets, i.e., either ferromagnets, antiferromagnets, or altermagnets. It is based on the belief that collinear magnets always feature an inversion-symmetric band structure, which forbids odd-parity magnetism. Here, we show that collinear magnets, which break time-reversal symmetry in the nonmagnetic sector, e.g., through loop currents, can have an inversion-symmetry-broken band structure and lead to unconventional types of collinear magnets. Hence, collinear odd-parity magnets do exist, and we explain that a magnetic field-induced Edelstein effect is their unique signature. We propose minimal models based on the coexistence of antiferromagnet order with compensated loop current orders for all types of collinear magnets. Our Letter provides a new perspective on collinear magnets and the spin-space group classification.

To gain deeper insight into the role of hole kinetics in determining magnetism in highly frustrated doped Mott insulators, we consider the single-hole counter-Nagaoka problem on the kagome lattice, using magnetization as a tuning parameter. Near full polarization, a doped hole delocalizes upon binding reversed spins in a pattern of singlet bonds which we term resonating-valence-bond (RVB) polaron. These RVB polarons can have extremely small effective bandwidths, and hence exhibit self-trapping. By tuning the spin polarization, we track the evolution of these states toward the unpolarized sector, where we observe the emergence of $\sqrt{3}\times \sqrt{3}$ antiferromagnetic correlation reminiscent of the classical Potts and Heisenberg models on the kagome lattice. These results provide a framework to understand how RVB physics at short scales evolves into conventional magnetic correlations at long scales.

We investigate the angle of repose ${\theta }_r$ of dense suspensions of colloidal silica particles ($d=2-7\mathrm{\mu m}$) in water-filled microfluidic rotating drum experiments to probe the crossover between the thermal (colloidal) and athermal (granular) regimes. For the smallest particles, thermal agitation promotes slow creep flows, and piles always flatten completely regardless of their initial inclination angle, resulting in ${\theta }_r=0$. Above a critical particle size, piles of colloids stop flowing at a finite angle of repose, which increases with particle size but remains below the minimal value expected for athermal frictionless granular materials: $0<{\theta }_r<{\theta }_{\mathrm{ath}}\approx 5.8°$. We quantify the arrest dynamics as a function of the gravitational Péclet number ${\mathrm{Pe}}_g$, which characterizes the competition between particle weight and thermal agitation. Our measurements are consistent with a recent rheological model [A. Billon et al., Phys. Rev. Fluids 8, 034302 (2023)], in which the arrested state stems from a crossover between glass and jamming transitions as the granular pressure in the pile increases relative to the thermal pressure.