Superconducting altermagnets have proven to be a promising ground for emergent phenomena, but their study has involved two-dimensional systems. In this work, we investigate three-dimensional $d$- and $g$-wave altermagnets with spin-singlet chiral $d$-wave superconductivity and show the formation of crossed surface flat bands due to the interplay between superconducting and altermagnetic symmetries. We find that these crossed flat bands are topologically protected, appear at zero energy in the surface along $z$ due to the superconducting nodal lines in the $xy$ plane, and their number of corners is determined by the crystal symmetry of altermagnets. We also show that the superconducting nodal lines give rise to Bogoliubov-Fermi surfaces, which then affect the appearance of zero-energy arcs in the surface along $x$. Moreover, we demonstrate that the crossed flat bands or surface arcs, and Bogoliubov-Fermi surfaces give rise to the coexistence of three distinct dependences of the charge conductance on the normal transparency, hence offering a solid way for their detection and paving the way for realizing higher-dimensional topological phases using altermagnets.

We report the experimental observation of magnetochiral anisotropy in the longitudinal and transverse ultrasound propagation in $\alpha$ quartz. To perform such measurement, we have built an ultrasound spectrometer with unprecedented experimental resolution of the order of $\mathrm{\Delta }v/v\sim {10}^{-8}$. We present a simple macroscopic Becquerel-like analytical model that accounts for the magnitude of the observed effect and its frequency dependence.

Bound states in the continuum (BICs), spatially localized states embedded in radiating continuum, have been extensively investigated in single-particle systems, also enabling high-performance applications in classical wave systems. Recently, exploring many-body BICs in correlated systems has emerged as a pivotal frontier with increasing research interest. However, the majority of previous studies focus largely on on-site interactions with tailored conditions, incurring significant implementation challenges. Whether off-site interactions, e.g., many-body hoppings, can generate many-body BICs and how to characterize them in experiments remains an open question. Here, we first predict and realize a boundary-localized two-body BIC, the bound pair state in the continuum (BPIC), arising from uniform two-body hoppings. Analytically, we demonstrate not just the formation of bound pairs, but the spectral coexistence of the boundary-localized BPIC and the scattering continuum. Experimentally, developing a phononic crystal platform as a classical-wave simulator, we map the correlated particle dynamics onto acoustic wave propagation and observe the acoustic BPIC. Our findings build a new bridge between the BIC research and many-body physics, and may promote the development of high-$Q$ acoustic devices in applications.

There is currently no rigorous definition of gravitational wave strain at second order in cosmological perturbation theory. The usual association of gravitational waves with transverse and traceless fluctuations of the metric on spatial hypersurfaces becomes ambiguous at second order, as it inherently depends on the spacetime slicing. While this poses no practical issues in linearized gravity, it presents a fundamental problem for secondary gravitational waves, especially notorious for gravitational waves induced by primordial fluctuations. We compute, for the first time, the observable gravitational wave strain at second order as measured by geodesic observers that emit and receive electromagnetic signals, thereby settling the debate on gauge ambiguities. Working in a gauge invariant fashion, we find that the measured gravitational wave strain coincides with the transverse-traceless components in the Newton gauge.

The interaction between free electrons and optical modes underlies a variety of quantum and nanoscale light-matter phenomena, yet the associated momentum exchange with the sample largely remained overlooked. Here, we experimentally demonstrate the momentum transfer from free electrons to planar samples during optical mode excitation using momentum-resolved electron energy-loss spectroscopy. The momentum transfer to the sample modifies the apparent dispersion relation which is significant when the planar sample is tilted. Under specific conditions, the sample receives momentum opposite to the electron beam direction.

Classical liquid–liquid phase separation predicts that droplets grow continuously via Brownian coalescence or Ostwald ripening, yet many nanoscale biomolecular condensates remain stable for hours or days without active regulation. Such condensates often arise through complex coacervation between oppositely charged macromolecules, making this interaction motif broadly relevant in biology and soft matter. Here we combine experiments, theory, and simulations to identify a merging-limited coarsening (MLC) regime in which merging of condensates decreases sharply below a critical droplet size. Chain-length asymmetry between oppositely charged polymers drives entropic interfacial charge separation even at globally neutral stoichiometry, imparting net droplet charges and generating long-range electrostatic repulsion. These size-dependent barriers lead to exponential rather than classical power-law growth and trap droplets in long-lived metastable states. Our framework unifies suppressed MLC and classical Brownian coalescence within a single predictive model and provides a general mechanism for condensate stability in both synthetic systems and living cells.

Decorating the superconducting Pb tip of a scanning tunneling microscope with a Mn atom cluster gives rise to Yu-Shiba-Rusinov resonances that serve as spin-sensitive probes of the tunneling current in junctions of single heptahelicene molecules adsorbed on Pb(111). The signal strength of these states in spectroscopy of the differential conductance depends on the handedness of the probed molecule, the direction of current flow, and the intramolecular site. These findings support the presence of the chirality-induced spin selectivity effect and the role of a single enantiomer as a spin polarizer.

${\text{FeF}}_2$ is a prototypical rutile antiferromagnet recently proposed as an altermagnet, with a magnetic symmetry that permits spin-split electronic bands and chiral magnons. Using very-high-resolution inelastic neutron scattering on a single crystal of ${\mathrm{FeF}}_2$, we show that the dominant source of magnon splitting is in fact the long-range dipolar interaction rather than altermagnetic exchange terms. At momenta where the dipolar splitting vanishes, we observe additional broadening due to altermagnetic chiral splitting and estimate this splitting to be $\sim 35\mathrm{\mu }\mathrm{eV}$. Polarized measurements further reveal that, where dipolar splitting is present, the chiral magnon modes become mixed and the resulting modes are predominantly linearly polarized, with at most a small chiral component. These findings highlight the significant effect of dipolar interactions on magnon chirality, particularly when altermagnetic interactions are weak.

Active semiflexible filament collectives, ranging from motor-driven cytoskeletal filaments to slender organisms such as cyanobacteria and worm aggregates, abound in nature. Yet how activity and flexibility jointly govern their organization, especially isotropic-nematic (I-N) transition, remains poorly understood. Performing large-scale Brownian dynamics simulations of 3D active semiflexible polymers with varying flexibility degrees, we show that tangential active forces systematically shift the I-N transition to higher densities, with the shift controlled by the flexibility degree and activity strength. Strikingly, activity alters the nature of the transition: discontinuous at low strengths, continuous at moderate strengths, and ultimately suppressed at high activity levels. The delayed I-N transition originates from enhanced collective bending fluctuations, resulting in chain shrinkage and enlargement of effective confinement tube. At moderate activity levels, these fluctuations can trigger large-scale excitations that stochastically drive temporal transitions between nematic and isotropic states, indicating an activity-induced instability of the nematic field. We summarize this behavior in nonequilibrium state diagrams of density and activity for different flexibility degrees.

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.