We show that a grating amplitude stationary in space but oscillating in time can be modeled as independent gratings traveling in opposite directions, interacting almost exclusively with waves traveling in the same direction. We reproduce the key features of traveling gratings: Amplification, field compression, and photon production are evident when the local wave speed equals the grating velocity. We speculate that these stationary but oscillating gratings may prove easier to realize experimentally than traveling gratings.

We study the dynamics of proliferating cell collectives whose microscopic constituents’ growth is inhibited by macroscopic growth-induced stress. Discrete particle simulations of a growing collective show the emergence of concentric-ring patterns in cell size whose spatiotemporal structure is closely tied to the individual cell’s stress response. Motivated by these observations, we derive a multiscale continuum theory whose parameters map directly to the discrete model. Analytical solutions of this theory show the concentric patterns arise from anisotropically accumulated resistance to growth over many cell cycles. This Letter shows how purely mechanical processes can affect the internal patterning and morphology of cell collectives, and provides a concise theoretical framework for connecting the micro- to macroscopic dynamics of proliferating matter.

In the presence of strong electronic interactions, a partially filled Chern band may stabilize a fractional Chern insulator (FCI) state, the zero-field analog of the fractional quantum Hall phase. While FCIs have long been hypothesized, feasible solid-state realizations only recently emerged, largely due to the rise of moiré materials. In these systems, the quantum geometry of the electronic bands plays a critical role in stabilizing the FCI in the presence of competing correlated phases. In the limit of “ideal” quantum geometry, where the quantum geometry is identical to that of Landau levels, this role is well understood. However, in more realistic scenarios only empiric numerical evidence exists, accentuating the need for a clear understanding of the mechanism by which the FCI deteriorates, moving further away from these ideal conditions. We introduce and analyze an anisotropic model of a $|C|=1$ Chern insulator, whereupon partial filling of its bands, an FCI phase is stabilized over a certain parameter regime. We incorporate strong electronic interaction analytically by employing a coupled-wires approach, studying the FCI stability and its relation to the quantum metric. We identify an unusual anti-FCI phase benefiting from nonideal geometry, generically subdominant to the FCI. However, its presence hinders the formation of FCI in favor of other competitive phases at fractional fillings, such as the charge density wave. Though quite peculiar, this anti-FCI phase may have already been observed in experiments at high magnetic fields. This establishes a direct link between quantum geometry and FCI stability in a tractable model far from any ideal band conditions, and illuminates a unique mechanism of FCI deterioration.

High-intensity lasers require suppression of prepulses and other nonideal temporal structure to avoid target disruption before the arrival of the main pulse. To address this, we demonstrate that ionization gratings act as a controllable optical switch for high-power light with a temporal contrast improvement of at least $3\times {10}^5$ and a switching time less than 500 fs. We also show that a grating system can run for hours at 10 Hz without degradation. The contrast improvement from an ionization grating compares favorably to that achievable with plasma mirrors.

Altermagnetism is a newly recognized magnetic class named after the alternating spin polarizations in both real and reciprocal spaces. Like the spin splitting of electronic bands, the magnon bands in altermagnets are predicted to exhibit alternating chiral splitting. In this work, by performing inelastic neutron scattering on $\alpha$-MnTe, we directly observed the altermagnetic magnon splitting. The lifted degeneracy of magnons is well explained by a symmetric-exchange origin. Further calculation based on the obtained spin-wave model demonstrates the magnons are chiral split as well. In addition, the $g$-wave magnetism was experimentally identified in MnTe.

Biological microswimmers alter their swimming trajectories to follow the direction of an applied electric field, exhibiting electrotaxis. We show that synthetic active droplet microswimmers also autonomously change swimming trajectories in microchannels, even undergoing “U-turns,” in response to an electric field, mimicking electrotaxis. We exploit such electrotaxis, in the presence of an external flow, to robustly tune the swimming trajectory of active droplets between wall-adjacent, oscillatory, and channel centerline swimming. A general hydrodynamic model demonstrates that the electrotactic dynamics is governed by the electrical effects due to the swimmer’s inherent surface charge, besides its motility, hydrodynamic wall interactions, and relative orientations of the electric field and imposed flow. Our study demonstrates a simple method for controlling active agents in complex geometries for microrobotic applications, like autonomous cargo delivery.

Biological and living organisms sense and process information from their surroundings, typically having access only to a subset of external observables for a limited amount of time. In this Letter, we uncover how biological systems can exploit these accessible degrees of freedom to transduce information from the inaccessible ones with a limited energy budget. We find that optimal transduction strategies may boost information harvesting over the ideal case in which all degrees of freedom are known, even when only finite-time trajectories are observed, at the price of higher dissipation. We apply our results to red blood cells, inferring the implemented transduction strategy from membrane flickering data and shedding light on the connection between mechanical stress and transduction efficiency. Our framework offers novel insights into the adaptive strategies of biological systems under nonequilibrium conditions.

The discovery of high-temperature superconductivity in ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ at pressures above 14 GPa has spurred extensive research efforts. Yet, fundamental aspects of the superconducting phase, including the possibility of a filamentary character, are currently subjects of controversial debates. Conversely, a crystal structure with ${\mathrm{NiO}}_6$ octahedral bilayers stacked along the $c$-axis direction was consistently posited in initial studies on ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$. Here, we reassess this structure in optical floating zone-grown ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ single crystals that show signs of filamentary superconductivity. Employing scanning transmission electron microscopy and single-crystal x-ray diffraction under high pressures, we observe multiple crystallographic phases in these crystals, with the majority phase exhibiting alternating monolayers and trilayers of ${\mathrm{NiO}}_6$ octahedra, signifying a profound deviation from the previously suggested bilayer structure. Using density functional theory, we disentangle the individual contributions of the monolayer and trilayer structural units to the electronic band structure of ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$, providing a firm basis for advanced theoretical modeling and future evaluations of the potential of the monolayer-trilayer structure for hosting superconductivity.

Dark photons that kinetically mix with the Standard Model photon give rise to new spectral anisotropies (patchy dark screening) in the cosmic microwave background (CMB) due to conversion of photons to dark photons within large-scale structure. We utilize predictions for this patchy dark screening signal to provide the tightest constraints to date on the dark photon kinetic mixing parameter [$ϵ\lesssim 4.5\times {10}^{-8}$ (95% confidence level)] over the mass range ${10}^{-13}\text{eV}\lesssim m_{A^{\prime }}\lesssim {10}^{-11}\mathrm{eV}$, almost an order of magnitude stronger than previous limits, by applying state-of-the-art component separation techniques to the cross-correlation of Planck CMB and unWISE galaxy survey data.

The associated production of Higgs and $W$ bosons via vector-boson fusion is highly sensitive to the relative sign of the Higgs boson couplings to $W$ and $Z$ bosons. In this Letter, two searches for this process are presented, using $140{\mathrm{fb}}^{-1}$ of proton-proton collision data at $\sqrt{s}=13\mathrm{TeV}$ recorded by the ATLAS detector at the LHC. The first search targets scenarios with opposite-sign couplings of the $W$ and $Z$ bosons to the Higgs boson, while the second targets standard model-like scenarios with same-sign couplings. Both analyses consider Higgs boson decays into a pair of $b$ quarks and $W$ boson decays with an electron or muon. The data exclude the opposite-sign coupling hypothesis with a significance beyond $5\sigma$, and the observed (expected) upper limit set on the cross section for vector-boson fusion $WH$ production is 9.0 (8.7) times the standard model value at 95% confidence level.

In three dimensions, quasi-one-dimensional (Q1D) transport has traditionally been associated with systems featuring a Q1D chain structure. Here, based on first-principle calculations, we go beyond this understanding to show that the Q1D transport can also be realized in certain three-dimensional (3D) altermagnetic (AM) metals with a topological nodal net in momentum space but lacking Q1D chain structure in real space, including the existing compounds $\beta \text{−}{\mathrm{Fe}}_2({\mathrm{PO}}_4)\mathrm{O}$, ${\mathrm{Co}}_2({\mathrm{PO}}_4)\mathrm{O}$, and ${\mathrm{LiTi}}_2{\mathrm{O}}_4$. These materials exhibit an AM ground state and feature an ideal crossed $Z^3$ Weyl nodal line in each spin channel around Fermi level, formed by three straight and flat nodal lines traversing the entire Brillouin zone. These nodal lines eventually lead to an AM $Z^3$ nodal net. Surprisingly, the electronic conductivity ${\sigma }_{xx}$ in these topological nodal net metals is dozens of times larger than ${\sigma }_{yy}$ and ${\sigma }_{zz}$ in the up-spin channel, while ${\sigma }_{yy}$ dominates transport in the down-spin channel. This suggests a distinctive Q1D transport signature in each spin channel, and the principal moving directions for the two spin channels are orthogonal, resulting in Q1D direction-dependent spin transport. This novel phenomenon cannot be found in both conventional 3D bulk materials and Q1D chain materials. In particular, the Q1D spin transport gradually disappears as the Fermi energy moves away from the nodal net, further confirming its topological origin. Our Letter not only enhances the comprehension of topological physics in altermagnets but also opens a new direction for the exploration of topological spintronics.

We show that two-dimensional fermions with dispersion $k^2$ or $k^4$ undergo a first-order Stoner transition to a fully spin-polarized state despite the fact that the spin susceptibility diverges at the critical point. We extend our analysis to systems with dispersion $k^{2\alpha }$ and spin and valley isospin and show that there is a cascade of instabilities into fractional-metal states with some electron bands fully depleted; narrow intermediate ranges of partially depleted bands exist for $\alpha <1$ or $\alpha >2$. The susceptibility becomes large near each transition. We discuss applications to biased bi- and trilayer graphene and moiré systems.

We demonstrate the excitation of the gyrotropic mode in a magnetostrictive vortex by time-varying strain. The vortex dynamics is driven by a time-varying voltage applied to the piezoelectric substrate and detected electrically by spin rectification at subthreshold values of rf current. When the frequency of the time-varying strain matches the gyrotropic frequency at a given in-plane magnetic field, the strain-induced in-plane magnetic anisotropy leads to a resonant excitation of the gyration dynamics in the magnetic vortex. We show that nonlinear gyrotropic dynamics can be excited already for moderate amplitudes of the time-varying strain.

A search for collective effects inside jets produced in proton-proton collisions is performed via correlation measurements of charged particles using the CMS detector at the CERN LHC. The analysis uses data collected at a center-of-mass energy of $\sqrt{s}=13\mathrm{TeV}$, corresponding to an integrated luminosity of $138{\mathrm{fb}}^{-1}$. Jets are reconstructed with the anti-$k_{\mathrm{T}}$ algorithm with a distance parameter of 0.8 and are required to have transverse momentum greater than 550 GeV and pseudorapidity $|{\eta }^{\text{jet}}|<1.6$. Two-particle correlations among the charged particles within the jets are studied as functions of the particles’ azimuthal angle and pseudorapidity separations ($\mathrm{\Delta }{\varphi }^{*}$ and $\mathrm{\Delta }{\eta }^{*}$) in a jet coordinate basis, where particles’ ${\eta }^{*}$, ${\varphi }^{*}$ are defined relative to the direction of the jet. The correlation functions are studied in classes of in-jet charged-particle multiplicity up to $N_{\mathrm{ch}}^{\mathrm{j}}\approx 100$. Fourier harmonics are extracted from long-range azimuthal correlation functions to characterize azimuthal anisotropy for $|\mathrm{\Delta }{\eta }^{*}|>2$. For low-$N_{\mathrm{ch}}^{\mathrm{j}}$ jets, the long-range elliptic anisotropic harmonic, $v_2^{*}$, is observed to decrease with $N_{\mathrm{ch}}^{\mathrm{j}}$. This trend is well described by Monte Carlo event generators. However, a rising trend for $v_2^{*}$ emerges at $N_{\mathrm{ch}}^{\mathrm{j}}\gtrsim 80$, hinting at a possible onset of collective behavior, which is not reproduced by the models tested. This observation yields new insights into the dynamics of jet evolution in the vacuum.

We report the observation of the melting of a vortex lattice in a fast rotating quasi-two dimensional Bose gas, under the influence of thermal fluctuations. We image the vortex lattice after a time-of-flight expansion, for increasing rotation frequency at constant atom number and temperature. We detect the vortex positions and study the order of the lattice using the pair correlation function and the orientational correlation function. We evidence the melting transition by a change in the decay of orientational correlations, associated with a proliferation of dislocations. Our findings are consistent with the hexatic to liquid transition in the Kosterlitz, Thouless, Halperin, Nelson, and Young scenario for two-dimensional melting.

A study of resonant structures in $B^{+}\to D^{*+}{D}^{-}{K}^{+}$ and $B^{+}\to D^{*-}{D}^{+}{K}^{+}$ decays is performed, using proton-proton collision data at center-of-mass energies of $\sqrt{s}=7$, 8, and 13 TeV recorded by the LHCb experiment, corresponding to an integrated luminosity of $9{\mathrm{fb}}^{-1}$. A simultaneous amplitude fit is performed to the two channels with contributions from resonances decaying to $D^{*-}{D}^{+}$ and $D^{*+}{D}^{-}$ states linked by $C$ parity. This procedure allows the $C$ parities of resonances in the $D^{*\pm }{D}^{\mp }$ mass spectra to be determined. Four charmonium or charmoniumlike states are observed decaying into $D^{*\pm }{D}^{\mp }$: ${\eta }_c(3945)$, $h_c(4000)$, ${\chi }_{c1}(4010)$, and $h_c(4300)$, with quantum numbers $J^{PC}$ equal to $0^{-+}$, $1^{+-}$, $1^{++}$, and $1^{+-}$, respectively. At least three of these states have not been observed previously. In addition, the existence of the $T_{\overline{c}\overline{s}0}^{*}(2870{)}^0$ and $T_{\overline{c}\overline{s}1}^{*}(2900{)}^0$ resonances in the $D^{-}{K}^{+}$ mass spectrum, already observed in the $B^{+}\to D^{+}{D}^{-}{K}^{+}$ decay, is confirmed in a different production channel.

Quantum sensing is crucial for precision measurements, yet quantum sensor sensitivity is often limited by the coherence time of the quantum system. Here, we demonstrate a method to enhance coherence time through cooperative spins. Using a tunable feedback circuit, we induce cooperation among noble-gas ${}^{129}\mathrm{Xe}$ spins, resulting in an impressive 18-fold coherence enhancement. Moreover, we show that the cooperative ${}^{129}\mathrm{Xe}$ spins can significantly amplify magnetic signals by at least 3 orders of magnitude. Magnetic field sensing assisted with such a cooperative spin amplifier realizes the sensitivity of $4\mathrm{fT}/{\mathrm{Hz}}^{1/2}$ and surpasses the spin-projection noise of the embedded ${}^{87}\mathrm{Rb}$ spin gas magnetometer. These results pave the way for a new class of “cooperative quantum sensors,” and open up exciting prospects in fundamental physics.

We show that the continuous time crystal state can arise in an ensemble of linear oscillators from nonconservative coupling via optical radiation pressure forces. This new mechanism comprehensively explains observations of the time crystal state in an array of nanowires illuminated with light [T. Liu et al., Nat. Phys. 19, 986 (2023).]. Being fundamentally different from regimes of nonlinear synchronization, it has relevance to a wide range of interacting many-body systems, including in the realms of chemistry, biology, weather, and nanoscale matter.

Electronic defects in semiconductors form the basis for emerging quantum technologies, but many defect centers are difficult to access at the single-particle level. A method for probing optically inactive spin defects would reveal semiconductor physics at the atomic scale and advance the study of new quantum systems. We exploit the intrinsic correlation between the charge and spin states of defect centers to measure the charge populations and dynamics of single substitutional nitrogen spin defects in diamond. By probing their steady-state spin population, read out at the single-defect level with a nearby nitrogen vacancy center, we directly measure the defect ionization—corroborated by first-principles calculations—an effect we do not have access to with traditional coherence-based quantum sensing.

Constraints on the quantum decoherence of entangled $\gamma$ quanta at the mega-electron-volt scale, such as those produced following positron annihilation, have remained elusive for many decades. We present the first statistically and kinematically precise experimental data for triple Compton scattering of such entangled $\gamma$. An entanglement witness ($R$), relating to the enhancement of the azimuthal correlation between the final scattering planes, is obtained where one of the $\gamma$ underwent intermediate Compton scattering. The measured $R$, deconvolved from multiple scattering backgrounds, are found to exceed the classical limit for intermediate scatter angles up to $\sim 60°$ and diminish at larger angles. The data are consistent with predictions from a first quantum theory of entangled triple Compton scattering as well as a simple model based approach. The results are crucial to future study and utilization of entangled mega-electron-volt $\gamma$ in fundamental physics and positron emission tomography imaging.