In this Letter, we show that the one-loop QCD $\beta$ function can be obtained from an index theorem on twistor space. This is achieved by recalling that the $\theta$ angle of self-dual gauge theory flows according the one-loop $\beta$ function. Rewriting self-dual gauge theory as a holomorphic theory on twistor space this flow can be computed as the anomaly to scale invariance. The one-loop Weyl anomaly coefficient $a\text{−}c$ can be recovered similarly.

We introduce a framework for computing time-dependent quantum transition rates (QTRs) that describe the pace of evolution of a quantum state from a given subspace to a target subspace. QTRs are expressed in terms of flux-flux correlators and are shown to obey two complementary quantum speed limits. Our framework readily accommodates the generalization of Hamiltonian dynamics to arbitrary open quantum evolution, including quantum measurements. We illustrate how QTRs can be controlled by counterdiabatic driving.

We present counterexamples to the lore that symmetries that cannot be gauged or made on site are necessarily anomalous. Specifically, we construct unitary, internal symmetries of two-dimensional lattice models that cannot be consistently coupled to background or dynamical gauge fields or disentangled to a tensor product of on-site operators. These symmetries are nevertheless anomaly-free in the sense that they admit symmetric, gapped Hamiltonians with unique, invertible ground states. We show that symmetries of this kind are characterized by an index $[\omega ]\in H^2(G,{\mathbb{Q}}_{+})$, where ${\mathbb{Q}}_{+}$ is the multiplicative group of positive rational numbers labeling one-dimensional quantum cellular automata.

We present the first direct measurement of the $Z=6$ shell gap in the neutron-rich ${}^{20}\mathrm{O}$ nucleus. The one-proton removal transfer reaction ${}^2\mathrm{H}({}^{20}\mathrm{O},{}^3\mathrm{He}){}^{19}\mathrm{N}$ has been studied using the ACTAR TPC setup at GANIL. The use of ACTAR TPC enabled the measurement of low-cross section proton-removal reactions while preserving resolution. Eight $p$-hole states with $\ell =1$ were identified in ${}^{19}\mathrm{N}$ accounting for total strengths of 86% and 72% of the $0p_{3/2}$ and $0p_{1/2}$ single-particle orbitals, respectively. The energies and spectroscopic factors of the measured states allowed to determine the proton spin-orbit splitting $\pi 0p_{3/2}-\pi 0p_{1/2}$ in ${}^{20}\mathrm{O}$. The $Z=6$ shell gap has been established to be 5.30(14) MeV. These findings indicate a reduction of the $Z=6$ shell gap while adding neutrons to the $sd$-valence orbitals, consistent with the effects of the tensor force predicted by state-of-the-art shell model interaction SFO-tls while at variance with the emergence of a large $Z=6$ gap observed in other studies.

We investigate the Reynolds-number dependence of the maximal Lyapunov exponent in fully developed turbulence, which quantifies the rate of chaotic divergence of nearby velocity fields. Using decorrelators constructed from infinitesimally perturbed flows, we find that the Lyapunov exponent scales with Reynolds number as $\lambda \sim {\mathrm{Re}}^{\alpha }$, with an exponent $\alpha =0.59\pm 0.04$ exceeding the classical mean-field prediction. By explicitly separating the nonlinear strain and viscous contributions to decorrelator growth, we show that this departure is associated by intermittent fluctuations of the strain-rate tensor, which dominate the short-time growth of the infinitesimal perturbations over viscous damping. Direct numerical simulations of the Navier-Stokes equations and complementary tests using a reduced shell model yield consistent scaling behavior, indicating robustness within the frameworks considered. Our results show that the dynamical origin of chaotic divergence in turbulence is closely linked to intermittent strain-rate fluctuations.

Among the family of intercalated transition-metal dichalcogenides (TMDs), ${\mathrm{Fe}}_x{\mathrm{NbS}}_2$ is found to possess unique current-induced resistive switching behaviors, tunable antiferromagnetic states, and a commensurate charge order, all of which are tied to a critical Fe doping of $x_c=1/3$. However, the electronic origin of such extreme stoichiometry sensitivities remains unclear. Combining angle-resolved photoemission spectroscopy (ARPES) with density functional theory (DFT) calculations, we identify and characterize a dramatic eV-scale electronic restructuring that occurs across the $x_c$. Moment-carrying Fe $3d_{z^2}$ electrons manifest as narrow bands within 200 meV of the Fermi level, distinct from other transition metal intercalated TMD magnets. These states strongly hybridize with itinerant electrons in the TMD layer and rapidly lose coherence above $x_c$ due to correlation-driven effects. This sudden quasiparticle decoherence collapses the Fe-Nb hybridization, which explicitly suppresses the out-of-plane effective Fe-Fe exchange interaction, driving the transformation of the magnetic ground state from an antiferromagnetic stripe phase to a zigzag phase. These observations resemble the exceptional electronic and magnetic sensitivity of strongly correlated systems, and demonstrate that quantifying orbital-specific hybridization via ARPES offers an alternative pathway to evaluate effective magnetic exchange in metallic magnets, complementing inelastic neutron and resonant x-ray scattering probes.

We investigate the impact of two-level systems (TLSs) on superconductivity, treating them as soft modes localized in real space. We show that these defects can either enhance or suppress the superconducting critical temperature, depending on their surface density and average frequency. Using thin-film aluminium as a case study, we quantitatively describe how TLSs modify both the critical temperature and the zero-temperature superconducting gap. Our results thus highlight new opportunities for tailoring material properties through TLS engineering.

We investigate from first principles the temperature-dependent electron-phonon ($e$-ph) renormalization of the fundamental band gaps of diamond, silicon, and gallium phosphide, with many-electron self-energy effects included, using the $GW$ and $GW$ perturbation theory methods for the band energy and $e$-ph coupling, respectively. Our results show that the $e$-ph renormalization of band gaps is enhanced by $\sim 50\%$ at the $GW$ level compared to results obtained with density functional theory (DFT) and density functional perturbation theory for all three materials. Moreover, the temperature dependence of the band gaps predicted by $GW$ and $GW$ perturbation theory shows excellent agreement with experimental measurements, with significant improvements from results at the DFT level. Our analysis reveals nonuniform $GW$ self-energy corrections, both in the $e$-ph coupling from different phonon modes and in the phonon-induced contributions (the Fan-Migdal and Debye-Waller terms) to the electron self-energy. Our findings emphasize the crucial role of many-electron effects in the temperature-dependent $e$-ph renormalization of band gaps and highlight the necessity of including $GW$ self-energy effects going beyond standard DFT approaches for accurate descriptions of $e$-ph phenomena.

We report observations of an energetic-particle mode (EPM) in a linear plasma device that corresponds to an axial bounce resonance of fast ions sourced from neutral-beam injection (NBI). In our experiment, novel dynamic shaping of a magnetic mirror field reduces the distance between the turning points of fast ions while introducing a minimum in the expected bounce frequency; this method decouples the plasma length from the fast-ion motion. We observe an axisymmetric magnetic mode with frequency evolution and axial extent that matches the predicted bounce motion. This experiment is repeated for two different NBI configurations with distinct bounce motions, thus confirming the mode’s origin as an axial bounce resonance. We then show that the EPM persists during a transition from a magnetic mirror to a field-reversed configuration (FRC), making this the first observation of an axial bounce resonance in an FRC. Additionally, we use the spatial structure of the EPM to diagnose the change in magnetic topology from mirror to FRC. Finally, a 2D simulation of the FRC formation accurately models the experimental observations and confirms that the mode arises from the clustering of resonant fast ions. These results have insightful implications for the control and design of linear fusion devices with substantial populations of fast ions.

We present an ab initio formalism based on the Bethe-Salpeter equation (BSE) to describe exciton-polaritons, capturing photonic and matter components on the same footing and obtaining polariton dispersions at the same cost as standard, static BSE calculations. We show in MgO that, near the light cone, the Bohr radii of excitons dramatically shrink by 50% while retaining primarily ($>75\%$) excitonic character. Our calculations agree well with experiments in CdS and can capture drastic changes in the exciton wave function in structurally complex materials, including crystalline pentacene.

We experimentally demonstrate boundary-induced helical bulk states (BI-HBSs) for rf acoustic transport in LiNbO3 thin-film phononic crystals ($\sim 175-200\mathrm{MHz}$). A boundary-symmetry selection rule at an accidental $\mathrm{\Gamma }$-point fourfold degeneracy creates interior bulk channels that couple to wide-aperture interdigital transducers without edge-aperture mismatch. Near-field vibrometry and two-port rf $S$ parameters confirm low-loss propagation with strongly suppressed backscattering through wavelength-scale defects. The helical band also provides slow-wave, low-dispersion delay and phase control on chip.

Heat waste is a bottleneck in the development of green information technologies and much effort has been devoted to suppress the heating effect in both electronic and spintronic devices. Here, we take an alternative approach and show that controllable heating at the nanoscale can actually benefit information processing. In particular, we study a hybrid nanostructure consisting of a metallic square frame and an antiferromagnetic (AFM) thin film and show that the plasmonic heating can reversibly switch two perpendicularly oriented AFM domains without the assistance of magnetic fields and electric currents. The required switching energy is at the order 1 nJ, 3 to 6 orders of magnitude lower than the current-driven AFM switching. The physical mechanism arises from the thermal-induced strain fields inside the frame, which couple to and manipulate the magnetic orientation via magnetoelastic effect. The strain field direction can be well controlled by selectively exciting the longitudinal and transverse plasmon modes by varying the polarization of the waves, which readily allows for a reversible switching of the AFM vector. Our findings provide tremendous opportunities for optically manipulating the magnetism with ultralow energy consumption and may further promote the interdisciplinary study of photonics, acoustics, and spintronics.

Photoexcitation has been utilized to control quantum matter and to uncover metastable phases far from equilibrium. Among demonstrations to date, the most common is the photoinduced transition from correlated insulators to metallic states; however, the reverse process without initial orders has not been observed. Here, we show ultrafast metal-to-insulator transition in gate-doped ${\mathrm{WS}}_2/{\mathrm{WSe}}_2$ and ${\mathrm{WSe}}_2/{\mathrm{WSe}}_2$ moiré devices using photothermionic hole injection from graphite gates. The resulting correlated insulators are metastable, with lifetimes exceeding microseconds. These findings establish an effective mechanism for the ultrafast control of correlated electronic phases in van der Waals (vdW) heterostructures.

Raman optical activity (ROA), the dependence of Raman intensity on the circular polarization of incident and scattered light, has traditionally been observed in chiral molecules and magnetic materials, where inversion or time-reversal symmetry is broken. Here we demonstrate that ROA can also arise in a centrosymmetric and nonmagnetic ferroaxial crystal. Using circularly polarized Raman spectroscopy on single-crystalline ${\mathrm{NiTiO}}_3$, we observed a pronounced ROA signal in the cross-circular polarization configurations, which correlates with the ferroaxial domain structure. Our symmetry analysis, first-principles calculations of phonons, and tight-binding model calculations reveal that the natural ROA originates from the ferroaxial order and persists even within the electric dipole approximation. These results establish ROA as a powerful probe of ferroaxial order in centrosymmetric systems.

We study diffusion on multiplex networks with directed interlayer couplings. We demonstrate both numerically and analytically that even with undirected layers, interlayer directionality alone reproduces superdiffusion and the prime regime. We further reveal a new phenomenon, the directionality-induced jamming, whereby directed interlayer links hinder diffusion, fragmenting the system into dynamically disconnected components and preventing convergence to the steady state of the diffusion process. Via an optimization process, we show that this new regime is attainable in both toy models and real-world topologies. These findings underscore the crucial role of interlayer link directionality in shaping the emergent behavior of multiplex systems, with potential implications for the design and control of such systems.

Atomically thin transition metal dichalcogenide heterobilayers represent promising platforms for next-generation optoelectronic devices, wherein interlayer excitons serve as carriers for energy and information transport. At the atomic scale, quantum many-body interactions give rise to rich correlation states that challenge classical transport models. However, direct insights into how these correlation states govern exciton dynamics have been limited by the constraints of conventional electrical measurements. Here, we directly image ultrafast exciton diffusion in ${\mathrm{WS}}_2/{\mathrm{WSe}}_2$ moiré superlattices and uncover a tunable cascade transport mechanism governed by the interplay between Hubbard interactions and correlated electron states. By independently tuning exciton and carrier populations via optical injection and electrostatic doping, we demonstrate that strong on-site Hubbard interactions can significantly enhance exciton mobility. In contrast, correlated electron phases—such as generalized Wigner crystals—dramatically suppress transport through enhanced exciton-electron scattering. These findings provide a quantum-based strategy for controlling exciton transport, offering a versatile framework for designing reconfigurable excitonic circuits and multifunctional quantum optoelectronic devices.

The theory of the intrinsic nonlinear Hall effect, a key probe of quantum geometry, is plagued by conflicting expressions for the conductivity that is independent of the dissipation strength (rate, ${\mathrm{\Gamma }}^0$). We clarify the origin of this ambiguity by demonstrating that the “intrinsic” response is not universal, but is inextricably linked to how the dissipation mechanism shapes the nonequilibrium steady state (NESS) density matrix. We establish a benchmark by solving the exact NESS density matrix for a generic Bloch system coupled to a featureless fermionic bath. Our exact ${\mathrm{\Gamma }}^0$ conductivity decomposes into two parts: (i) a geometric contribution, ${\sigma }^{\mathrm{geo}}$, which establishes the definitive structure of the quantum metric contribution (including the intraband $\sim {\partial }_{k}g$ term), clarifying inconsistencies in the literature, and (ii) a novel, purely kinetic contribution, ${\sigma }^{\mathrm{kin}}\propto v^3{f}_0^{(4)}$, arising from mechanism-specific modifications to the occupation functions, which is absent in approaches that postulate, rather than derive, the relaxation dynamics. The discrepancies in both ${\sigma }^{\mathrm{geo}}$ and ${\sigma }^{\mathrm{kin}}$ between these distinct physical mechanisms prove that the ${\mathrm{\Gamma }}^0$ nonlinear conductivity is not a unique property of the Bloch Hamiltonian, but is contingent on the physical system-bath coupling.

We derive an inequality relating the finite-frequency linear response and fluctuations of an observable in a physical system in steady state. The relation holds for arbitrary observables and perturbations in general Markovian dynamics, including overdamped and underdamped Langevin systems and jump processes, both in and out of equilibrium. As a consequence, we obtain a universal upper bound on the broadband signal-to-noise ratio of noisy dynamics, which only depends on the damping constant and temperature. We further show that the inequality reduces to an equality for appropriately chosen observables or perturbations in linear systems, both overdamped and underdamped and both in and out of equilibrium.

Fractionally charged elementary excitations, the quasielectron and quasihole, are hallmarks of the fractional Chern insulator. We observe that spontaneous spin polarization in twisted ${\mathrm{MoTe}}_2$ leads to multiple species of low-energy quasiparticles distinguished by their spin quantum numbers. Through large-scale exact diagonalization calculations, we investigate the nature of these excitations and develop a method to extract their energetic properties. Focusing on $\theta =3.7°$ and filling factor $\nu =-2/3$ relevant to recent experiments, we show that spin-preserving (spinless) charge excitations have smaller gap than spin-flipping (spinful) excitations with and without band mixing. This result is in qualitative agreement with the measured magnetic field dependence of the transport gaps. Beyond spinless and spinful quasiparticle gaps, we extract the full quasielectron and quasihole “band structure” and find significant dispersion with emergent magnetic translation symmetry—a fundamental departure from the immobile excitations of the quantum Hall fluid. Our work establishes a framework for computing the properties of elementary excitations in fractional Chern insulators.