The absence of a well-defined Fermi surface in flat-band systems challenges the conventional understanding of instabilities toward Landau order based on nesting. We investigate the existence of an intrinsic nesting structure encoded in the band geometry [i.e., the wave functions of the flat band(s)], which leads to a maximal susceptibility at the mean-field level and, thus, determines the instability toward ordered phases. More generally, we show that, for a given band structure and observable, we can define two vector fields: one which corresponds to the Bloch vector of the projection operator onto the manifold of flat bands and another which is “dressed” by the observable. The overlap between the two vector fields, possibly shifted by a momentum vector $\mathit{Q}$, fully determines the mean-field susceptibility of the corresponding order parameter. When the overlap is maximized, so is the susceptibility, and this geometrically corresponds to “perfect nesting” of the band structure. In that case, we show that the correlation length of this order parameter, even for $\mathit{Q}\ne \mathbf{0}$, is entirely characterized by a generalized quantum metric in an intuitive manner and is, therefore, lower bounded in topologically nontrivial bands. As an example, we demonstrate hidden nesting for staggered antiferromagnetic spin order in an exactly flat-band model, which is notably different from the general intuition that flat bands are closely associated with ferromagnetism. We check the actual emergence of this long-range order using the determinantal quantum Monte Carlo algorithm. Additionally, we demonstrate that a Fulde-Ferrell-Larkin-Ovchinnikov-like state (pairing with nonzero center of mass momentum) can arise in flat bands upon breaking time-reversal symmetry, even if Zeeman splitting is absent.

We present a first joint extraction of the Collins-Soper kernel (CSK) combining experimental and lattice QCD data in the context of an analysis of transverse-momentum-dependent distributions (TMDs). Based on a neural-network parametrization, we perform a Bayesian reweighting of an existing fit of TMDs using lattice data, as well as a joint TMD fit to lattice and experimental data. We consistently find that the inclusion of lattice information shifts the central value of the CSK by approximately 10% and reduces its uncertainty by 40%–50%, highlighting the potential of lattice inputs to improve TMD extractions.

Parton distribution functions (PDFs) are central to precision QCD phenomenology. Their Mellin moments can be computed on the lattice, but direct determinations using local operators, besides $⟨x⟩$, face severe challenges from reduced hypercubic symmetry, limiting results to the lowest moments. A recently proposed method resolves these issues using gradient flow. We demonstrate the efficacy of this method by computing ratios of flavor nonsinglet pion PDF moments up to $⟨x^5⟩$ on four lattice spacings at $m_{\pi }\simeq 411\mathrm{MeV}$. The moments and reconstructed PDF agree quantitatively with recent phenomenological extractions.

The scaling exponent $g$ of the quasiparticle propagator for incompressible fractional quantum Hall states in the Laughlin sequence is expected to be robust against perturbations that do not close the gap. Utilizing a novel AlGaAs/GaAs heterostructure designed to produce sharp edge confinement, we probe the robustness of the chiral Luttinger liquid at the boundary of the $\nu =1/3$ state by measuring the tunneling conductance between counterpropagating edge modes. We demonstrate that for transmission $t\ge 0.7$ the tunneling conductance is well-described by the first two terms of a perturbative series expansion corresponding to $g=1/3$. We demonstrate that the measured scaling exponent is robustly pinned to $g=1/3$ across the plateau, only deviating as the bulk state becomes compressible. We examine the impact of weak disorder on the scaling exponent, finding it insensitive. These measurements establish the topological robustness of anyon tunneling at $\nu =1/3$ and substantiate the chiral Luttinger liquid description of the edge mode.

Nuclear-spin conversion in molecular hydrogen is governed by strict symmetry rules that typically require magnetic fields or catalytic surfaces to break. Here we demonstrate that the intrinsic tensor composition of a nonmagnetic molecular crystal field can impose and relax these rules without external fields. High-resolution infrared spectra of ${\mathrm{H}}_2$ in crystalline ${\mathrm{CO}}_2$ reveal large rank-2 (quadrupolar) crystal-field splittings of the $m$ sublevels, while nuclear-spin conversion occurs only through $\mathrm{\Delta }m=0$ channels. Replacing ${\mathrm{CO}}_2$ with polar ${\mathrm{N}}_2\mathrm{O}$ introduces rank-1 (dipole) components that partially open $\mathrm{\Delta }m\ne 0$ pathways, while incorporation of paramagnetic ${\mathrm{NO}}_2$ fully lifts the restriction. These results establish a direct correspondence between crystal-field tensor rank and nuclear-spin dynamics, introducing a general symmetry-based framework for designing and controlling spin-isomer populations and quantum-state connectivity in molecular solids.

We demonstrate that superconductivity driven by strong quantum-critical fluctuations can emerge near relativistic Mott transitions in twisted two-dimensional materials. In twisted double-bilayer ${\mathrm{WSe}}_2$, all time-reversal-even, gap-opening collective modes promote pairing, whereas time-reversal-odd modes do not. In twisted bilayer graphene, all transitions into intervalley-coherent insulators give rise to superconductivity. Hence, the two separate superconducting domes of insulating or semimetallic undoped systems are expected to merge near the Gross-Neveu transition angle. A crucial ingredient of the theory is that critical fluctuations render the electronic states strongly incoherent, allowing attractive pairing channels to overcome the bare Dirac semimetal behavior. The richer the Dirac structure, the more readily pairs can form. Finally, we demonstrate a direct relation between boson-mediated pairing and the formation of charge-carrying skyrmions in the proximate insulating state.

The advent of wurtzite ferroelectrics is enabling new ferroelectric devices for computer memory that have the potential to bypass the von Neumann bottleneck due to their robust polarization and silicon compatibility. However, the atomistic switching mechanism of wurtzites is still undetermined due to the limitations of density functional theory simulation size and experimental temporal and spatial resolution. Thus, physics-informed materials engineering to reduce coercive field and breakdown in these devices has been limited. Here, the atomistic mechanism of domain wall migration and domain growth in aluminum nitride-based wurtzites is uncovered using molecular dynamics and Monte Carlo simulations. We reveal the anomalous switching mechanism of fast 1D single columns of atoms propagating from a slow-moving 2D fractallike domain wall. We find that the critical nucleus is a single aluminum ion that breaks its bond with one nitrogen and bonds to another nitrogen; this creates a cascade that flips atoms directly only in the same column, due to the extreme locality (sharpness) of the domain walls in wurtzites. We further show how the fractallike shape of the domain wall in the 2D plane breaks assumptions in the Kolmogorov, Avrami, and Ishibashi (KAI) model and leads to the anomalously fast switching in wurtzite structured ferroelectrics.

Understanding mechanisms of rare but important events in complex molecular systems, such as protein folding or ligand (un)binding, requires accurately mapping transition paths from an initial to a final state. The committor is the ideal reaction coordinate for this purpose, but calculating it for high-dimensional, nonlinear systems has long been considered intractable. Here, we introduce an iterative path-sampling strategy for computing the committor function for systems with high free-energy barriers. We start with an initial guess to define isocommittor interfaces for transition interface sampling. The resulting path ensemble is then reweighted and used to train a neural network, yielding a more accurate committor model. This process is repeated until convergence, effectively solving the long-standing circular problem in enhanced sampling where a good reaction coordinate is needed to generate efficient sampling, and vice versa. The final, converged committor model can be interrogated to extract mechanistic insights. We demonstrate the power of the method on a benchmark 2D potential and a host-guest (un)binding process in an explicit solvent.

Supernova remnants (SNRs) have been considered as the primary contributors to cosmic rays (CRs) in our Galaxy. However, the maximum energy of particles that can be accelerated by shocks of SNRs is uncertain, and SNRs’ contribution to CRs around PeV energies is unclear. In this Letter, we present observations of high-energy $\gamma$-ray emission from the SNR IC 443 using the Large High Altitude Air Shower Observatory (LHAASO). The morphological analysis reveals a pointlike source whose location and spectrum are consistent with those of the Fermi-LAT-detected compact source with ${\pi }^0$-decay signature, and a more extended source that is associated with a newly discovered Fermi source. The spectrum of the point source can be described by a power-law function with an index of $\sim 3.0$, extending beyond $\sim 30\mathrm{TeV}$ without apparent cutoff. Assuming a hadronic origin of the $\gamma$-ray emission, the 95% lower limit of accelerated protons reaches about 300 TeV. The extended source might be associated with IC 443, SNR $\mathrm{G}189.6+3.3$, or the putative pulsar wind nebula CXOU $\mathrm{J}061705.3+222127$, and can be explained by either a hadronic or a leptonic model with particles reaching hundreds of TeV. These LHAASO results provide compelling evidence that sub-PeV CRs can be accelerated efficiently by shocks of SNRs.

The spontaneous emergence of chirality in crystalline solids has profound implications for electronic, optical, and topological properties, making the control of chiral phases a central challenge in materials design. Here, we investigate the structural and electronic properties of a new family of layered compounds, ${\mathrm{NbOX}}_2$, and explore the connection between their achiral $Immm$ phase and chiral $C2$ phase. Through first-principles calculations, we identify an intermediate achiral $C2/m$ phase that bridges the high- and low-symmetry phases within a three-dimensional order parameter space. By analyzing the Born-Oppenheimer energy surfaces, we find that the shallow energy minima of the $C2/m$ phase suggest it may be stabilized either by external factors such as pressure, as demonstrated here, or by ionic quantum or thermal fluctuations and the resulting lattice anharmonicity. Additionally, we show how an external electric field, by breaking the necessary symmetries, biases the system toward a preferred chirality by lifting the energy degeneracy between the two enantiomers. This, combined with the small energy barrier between the enantiomers in the $C2$ phase, enables handedness control and allows us to propose a mechanism for selective handedness stabilization by leveraging electric fields and pressure or temperature-dependent anharmonic effects. Our findings establish a framework for understanding chirality emergence in layered materials and offer a pathway for designing systems with tunable enantiomeric populations.

Recent observations of quantum anomalous Hall effects in moiré systems have revealed the emergence of interaction-driven ferromagnetism with significant orbital contributions. To capture this physics, we extend the modern theory of orbital magnetization to Hartree–Fock states and show that the standard expression remains valid with Hartree–Fock orbitals and Hamiltonians. Then, we benchmark our theory against the extended Kane-Mele-Hubbard model in a weak field, which yields excellent agreement with direct numerical calculations. Applying our theory to twisted ${\mathrm{MoTe}}_2$ bilayers, we find orbital magnetization of order one Bohr magneton per moiré cell with a nonmonotonic twist-angle dependence. Our work establishes a general theory of orbital magnetization in interacting moiré systems and provides quantitative guidance for interpreting recent experiments.

A hot and dense state of nuclear matter, known as the quark-gluon plasma, is created in collisions of ultrarelativistic heavy nuclei. Highly energetic quarks and gluons, collectively referred to as partons, lose energy as they travel through this matter, leading to suppressed production of particles with large transverse momenta ($p_{\mathrm{T}}$). Conversely, high-$p_{\mathrm{T}}$ particle suppression has not been seen in proton-lead collisions, raising questions regarding the minimum system size required to observe parton energy loss. Oxygen-oxygen (OO) collisions examine a region of effective system size that lies between these two extreme cases. The CMS detector at the CERN LHC has been used to quantify charged-particle production in inclusive OO collisions for the first time via measurements of the nuclear modification factor ($R_{\mathrm{AA}}$). The $R_{\mathrm{AA}}$ is derived by comparing particle production to expectations based on proton-proton ($pp$) data and has a value of unity in the absence of nuclear effects. The data for OO and $pp$ collisions at a nucleon-nucleon center-of-mass energy $\sqrt{s_{\mathrm{NN}}}=5.36\mathrm{TeV}$ correspond to integrated luminosities of $6.1{\mathrm{nb}}^{-1}$ and $1.02{\mathrm{pb}}^{-1}$, respectively. The $R_{\mathrm{AA}}$ is below unity with a minimum of $0.69\pm 0.04$ around $p_{\mathrm{T}}=6\mathrm{GeV}$. The data exhibit better agreement with theoretical models incorporating parton energy loss as compared to baseline models without energy loss.

Nonuniform strain in graphene acts as a valley-dependent gauge field, generating pseudomagnetic fields (PMFs) that mimic real magnetic fields while preserving global time-reversal symmetry. While such fields have been visualized locally, their quantitative detection via macroscopic transport has remained elusive. Here, we show that graphene exhibits distinct beating patterns in Shubnikov-de Haas oscillations arising from valley-resolved Landau quantization under different effective magnetic fields. Systematic analysis of the beating nodes reveals universal quadratic and linear scaling of the carrier density and Landau level filling factor with magnetic field, enabling the extraction of PMFs of order millitesla. Our results establish quantum oscillation spectroscopy as a robust transport probe of strain-induced gauge fields in Dirac materials and open avenues for mechanically tunable valleytronic and straintronic devices.

In antiferromagnetic spintronics, accessing the spin degrees of freedom is essential for generating spin currents and manipulating magnetic order, which generally requires lifting spin degeneracy. This is typically achieved through relativistic spin-orbit coupling or nonrelativistic spin splitting in altermagnets. Here, we propose an alternative approach: a dynamical spin splitting induced by an optical field in antiferromagnets. By coupling the driven system to a thermal bath, we demonstrate the emergence of steady-state pure spin currents as well as linear-response longitudinal and transverse spin currents. Crucially, thermal bath engineering enables a nonrelativistic Edelstein effect—the generation of a net spin accumulation—without relying on spin-orbit coupling. Our results provide a broadly applicable and experimentally tunable route to control spins in antiferromagnets, offering new opportunities for spin generation and manipulation in antiferromagnetic spintronics.

Time-resolved measurement of Auger-Meitner decay [Drescher et al., Nature (London) 419, 803 (2002)] marked a milestone in the development of attosecond science. To date, the time constants for the Auger-Meitner decay processes obtained from the time-domain experiments were found to be consistent with the values deduced from conventional energy-domain measurements. One of the main factors limiting the temporal resolution of these studies is the unlocked carrier-envelope-phase (CEP) of the laser pulses used to probe the electronic dynamics triggered by inner-shell photoabsorption. In this Letter, we report time-resolved inner-shell electron spectroscopy of xenon and krypton using attosecond soft x-ray (atto-SXR) pulses centered at 130 eV in combination with CEP-stabilized few-cycle Yb laser pulses. We observed that the $N_{4,5}\mathrm{OO}$ Auger electrons from xenon exhibit a clear streaking pattern, but with an unexpected time shift of $\sim 1.32\mathrm{fs}$ relative to the $4d$ photoelectrons. Furthermore, the energy-integrated yield of streaked Auger electrons from xenon exhibits a pronounced minimum at a pump-probe time delay of 4 fs. Neither of these observations can be explained by current streaking theories and both are inconsistent with lifetimes inferred from energy-domain measurements. The $M_{4,5}\mathrm{NN}$ Auger electrons from krypton partly overlap in energy with the $3d$ inner-shell photoelectrons and do not show these anomalous features. This Letter offers new insights into the inner-shell electron dynamics of heavy atoms in the giant dipole resonance region, laying the groundwork for attosecond soft x-ray spectroscopy of molecular systems containing iodine or bromine atoms.

Optical clocks based on atoms and ions probe relativistic effects with unprecedented sensitivity. They resolve time dilation due to atom motion or different positions in the gravitational potential through frequency shifts. However, all measurements of time dilation so far can be explained effectively as the result of dynamics with respect to a classical proper time parameter. Here we show that atomic clocks can probe effects where a classical description of the proper time dynamics is insufficient as superpositions of proper time emerge. We apply a Hamiltonian formalism to derive time dilation effects in harmonically trapped clock atoms and show how second-order Doppler shifts due to the vacuum energy, squeezing, and quantum corrections to the dynamics arise. We also demonstrate that time-dilation-induced entanglement between motion and clock evolution can become observable in state-of-the-art clocks when the motion of the atoms is strongly squeezed, realizing proper time interferometry. Our results show that experiments with trapped ion clocks are within reach of probing relativistic evolution of clocks for which a quantum description of proper time becomes necessary.

Electronic nematicity is widely observed in quantum materials with varying degrees of electronic correlation, manifesting through charge, spin, orbital, or superconducting degrees of freedom. A phenomenological model capable of describing this broad set of systems must also account for nematoelasticity, by which nematic and elastic degrees of freedom become intertwined. However, being a tensor gauge field theory, elasticity must satisfy the compatibility relations which guarantee the integrability of lattice deformations. Here, we develop a formalism for nematoelasticity that manifestly respects the elastic compatibility relations. We show that these constraints bifurcate the phase space of nematic fluctuations into two orthogonal sectors: one compatible and thus critical, the other incompatible and therefore gapped. The suppression of the latter leads to universal direction-selective nematic criticality in any crystal lattice. Moreover, the critical nematic modes are protected from pinning effects induced by microscopic defect strains, which necessarily induce both longitudinal and transverse correlated random fields. Finally, our results also reconcile seemingly contradictory nematic phenomena, such as the mean-field character of the nematic transition and the widespread presence of domain formation.

We present the first experimental evidence for in-ice Askaryan radiation—coherent charge-excess radio emission—from high-energy particle cascades developing in the Antarctic ice sheet. In 208 days of data recorded with the phased array instrument of the Askaryan Radio Array, a previous analysis has incidentally identified 13 events with impulsive radio frequency signals originating from below the ice surface. We here present a detailed reanalysis of these events. The observed event rate, radiation arrival directions, signal shape, spectral content, and electric field polarization are consistent with in-ice Askaryan radiation from cosmic ray air shower cores impacting the ice sheet. For the brightest events, the angular radiation pattern favors an extended cascadelike emitter over a pointlike source. An origin from the geomagnetic separation of charges in cosmic ray air showers is disfavored by the arrival directions and polarization. Considering the arrival angles, timing properties, and impulsive nature of the passing events, the event rate is inconsistent with the estimation of the combined background from thermal noise events and on-surface events at the level of $5.1\sigma$.

Shear-thickening suspensions—materials that abruptly become more viscous or jam under stress—are widespread in nature and industry. Yet their dynamics in gravity-driven flows remain poorly understood. Here, we show that such suspensions spread by forming a sharp, vertical front—a liquid dam—that advances at a constant speed, independent of released volume, flow height, and slope. This counterintuitive behavior arises from a jammed, frictional front that localizes dissipation and decouples flow dynamics from geometry. A simple gravito-rheological model predicts the observed constant-speed regime, with a velocity scale set by the suspension rheology. The same scaling governs spreading and wave propagation across diverse flow configurations, revealing how shear thickening can critically shape gravity-driven flows in both natural and industrial settings.

In this Letter, we explore two-dimensional attractive Fermi gases at the microscopic level by probing spatial charge and spin correlations in situ. Using atom-resolved continuum quantum gas microscopy, we directly observe fermion pairing and study the evolution of two- and three-point correlation functions as interspin attraction is increased. The precision of our measurement allows us to reveal nonlocal anticorrelations in the pair correlation function, fundamentally forbidden by the mean-field result based on BCS theory but whose existence we confirm in exact auxiliary-field quantum Monte Carlo calculations. We demonstrate that the BCS prediction is critically deficient not only in the superfluid crossover regime but also deep in the weakly attractive side. Guided by our measurements, we find a remarkable relation between two- and three-point correlations that establishes the dominant role of pair correlations. Finally, leveraging local single-pair losses, we independently characterize the short-range behavior of pair correlations, via the measurement of Tan’s contact, and find excellent agreement with numerical predictions. Our measurements provide a novel microscopic view into strongly correlated two-dimensional Fermi gases in the continuum.