We study the sedimentation of finite-size inertial particles in a Rayleigh-Taylor-like setup using state-of-the-art direct numerical simulations. The falling particles are observed to produce two distinct regions: a leading mixing layer with a linear concentration profile followed by a bulk region of uniform density. Unlike classical RT turbulence, the mixing layer extension accelerates with an anomalous, noninteger exponent, while the bulk region moves at a constant velocity. A one-dimensional model based on a local hindered settling law accurately captures the observed dynamics and its dependence on the particle-to-fluid density ratio. The present Letter identifies a new regime of convective mixing which develops at the front of particle suspensions in sedimentation processes.

Electric control over magnetic interactions at the level of individual spins is relevant for a variety of quantum applications, such as qubits, memory, and sensor functionality. We show here that spin lattices and magnon gaps can be controlled with a supercurrent. Remarkably, a spin-polarized supercurrent makes the interaction between magnetic adatoms placed on the surface of a superconductor depend not only on their relative distance, but also on their absolute position in space. This property permits electric control over the interaction not only between two individual spins, but over an entire spin lattice, allowing for tunable noncollinear ground states and a practical arena to study the properties of different spin Hamiltonians. Moreover, we show that a supercurrent controls the magnon gap in antiferromagnetic and altermagnetic insulators. These results provide an accessible way to realize electrically controlled spin switching and magnon gaps without dissipative currents.

Altermagnets hold great potential for spintronic applications, yet their intrinsic spin dynamics and associated transport properties remain largely unexplored. Here, we investigate spin-resolved quantum transport in a multiterminal setup based on a $d$-wave altermagnet. It is found that the altermagnetic spin splitting in momentum space induces an interesting spin precession in two-dimensional real space, giving rise to characteristic spin patterns. This altermagnetic spin precession manifests as a spatial modulation of the transverse Hall-like voltage, whose oscillation period provides a direct measure of the spin-splitting strength. When the altermagnetism is electrically tunable, the proposed setup functions as a prototype for a highly efficient spin transistor. The key physical effects are shown to be robust against dephasing and crystalline warping. Our Letter not only identifies a fingerprint signature of altermagnets, offering a direct probe of the altermagnetic spin splitting, but also represents an important step toward bridging their fundamental physics with practical spintronic applications.

Antiferroelectricity is a fundamental concept in physics and materials science. Conventional antiferroelectrics (AFEs) have the picture of alternating local electric dipoles defined in real space. Here, we discover a new class of AFEs, termed type-II AFEs, which possess opposite polarizations defined in momentum space across a pair of symmetry decoupled subspaces. Unlike conventional AFEs, the order parameter of type-II AFEs is rigorously formulated through Berry-phase theory and can be quantitatively extracted from the electronic band structure. Focusing on a subclass of type-II AFEs that preserve spin-rotation symmetry, we establish the relevant symmetry constraints and identify all compatible spin point groups. Remarkably, we find that type-II AFE order intrinsically coexists with antiferromagnetism, revealing a robust form of magnetoelectric coupling. We construct an altermagnetic model and identify several concrete antiferromagnetic and altermagnetic materials, such as FeS, ${\text{Cr}}_2{\mathrm{O}}_3$, ${\mathrm{MgMnO}}_3$, monolayer ${\mathrm{MoICl}}_2$ and bilayer ${\mathrm{CrI}}_3$, that exhibit this novel ordering. Furthermore, we uncover unique physical phenomena associated with type-II spin-AFEs including spin current generation upon AFE switching and localized spin polarization at boundaries and domain walls. Our findings reveal a previously hidden class of quantum materials with intertwined ferroic orders, offering exciting opportunities for both fundamental exploration and technological applications.

We introduce a new class of tunable periodic structures formed by launching two obliquely propagating surface acoustic waves on a piezoelectric substrate that supports a two-dimensional material. The resulting acoustoelectric superlattice exhibits two salient features. First, its periodicity is widely tunable, spanning a length scale intermediate between moiré superlattices and optical lattices, enabling the formation of narrow, topologically nontrivial energy bands. Second, unlike moiré systems, where the superlattice amplitude is set by intrinsic interlayer tunneling and lattice relaxation, the amplitude of the acoustoelectric potential is externally tunable via the surface acoustic wave power. Using massive monolayer graphene as an example, we demonstrate that varying the frequencies and power of the surface acoustic waves enables in situ control over the band structure of the 2D material, generating flat bands and nontrivial valley Chern numbers, featuring a highly localized Berry curvature.

Translation symmetry-breaking order is assumed to be suppressed by the lack of Fermi surface nesting near certain higher-order Van Hove singularities (HOVHS). We show that the anisotropic band-flattening inherent to such HOVHS, combined with broadening of the Fermi surface due to elevated critical scales, results in the Fermi surface becoming approximately nested at a wave vector unrelated to the precise shape of the Fermi surface—leading to a $\sqrt{3}\times \sqrt{3}$ Kekulé density wave formation. The effect is demonstrated using unbiased renormalization group calculations for a model of the breathing kagome lattice. Our mechanism—termed diffuse nesting—represents an entirely new notion in the study of Fermi surface instabilities.

Iron chalcogenide superconductors ${\text{FeSe}}_{1-x}{\mathrm{Ch}}_x$ ($\mathrm{Ch}=\mathrm{S},\mathrm{Te}$) exhibit an unusual double-dome superconducting phase diagram, the microscopic origin of which remains unclear. Here, we use inelastic neutron scattering to probe spin excitations in single-crystalline $\mathrm{Fe}{\mathrm{Se}}_{0.67}{\mathrm{Te}}_{0.33}$, positioned at the superconducting transition temperature ($T_{\mathrm{c}}$) minimum between the two domes. We identify two distinct spin excitation components separated by a crossover energy ($E_{\mathrm{c}}\approx 30\mathrm{meV}$). Below $E_{\mathrm{c}}$ the spin excitations emanate from the stripe-type wave vector (1,0), with their intensity strongly suppressed upon warming above the nematic transition at $T_{\mathrm{s}}\approx 40\mathrm{K}$, revealing strong coupling between them. Above $E_{\mathrm{c}}$ the high-energy excitations disperse more steeply and display little temperature dependence across $T_{\mathrm{s}}$. Further warming from $T_{\mathrm{s}}$ to 300 K results in the gradual downward evolution of the high-energy spin excitations, reaching an incommensurate wave vector near $(1,\pm 0.3)$ at the low-energy limit. The combined energy- and temperature-dependent responses point to competition between stripe and incommensurate excitations, which can contribute to the reduced $T_{\mathrm{c}}$ near the valley composition; while Te substitution may simultaneously tune the electronic structure in ways that could coexist with, or reinforce, this competition. These findings illuminate the intricate interplay of multiple components of magnetic excitations in shaping $T_{\mathrm{c}}$ of iron chalcogenides.

Equilibrium interlayer exciton condensation is common in bilayer quantum Hall systems and is characterized by spontaneous phase coherence between isolated layers. It has been predicted that similar physics can occur in the absence of a magnetic field in some two-dimensional semiconductor bilayers. In this Letter we consider the case of two transition metal dichalcogenide (TMD) monolayers separated by a twisted hexagonal boron nitride (hBN) bilayer or multilayer. The hBN layers suppress tunneling between the TMD layers so that phase coherence is spontaneous when it is present. When twisted, the hBN layers also form a ferroelectric moiré pattern that applies opposite triangular-lattice modulation potentials to the two TMD layers. We show via mean-field theory that at total hole filling per moiré unit cell $\nu =1$, this geometry can favor a chiral $p$-wave exciton condensate state in which the quantum anomalous Hall effect coexists with counterflow superfluidity. We present a mean-field phase diagram for TMD hole bilayers modulated by twisted hBN, discuss the conditions needed for the realization of the $p$-wave condensate state, and propose experiments that could confirm its presence.

Photonic media modulated periodically in time, termed photonic time crystals (PTCs), have attracted considerable attention for their ability to open momentum bandgaps hosting amplifying modes. These momentum gaps, however, generally appear only at the system’s parametric resonance condition which constrain many features derived from amplification to a narrow frequency band. Moreover, they are accompanied by exceptional points (EPs) and may drive the system into an instability, which renders their analysis more intricate. Here, we show that a careful consideration of dispersion and absorption can overcome these issues. By investigating the dissipated power of a point-dipole embedded in a dispersive and absorptive PTC, we unveil that temporal modulation enables the conversion of dipole emission into dipole absorption within a broadband frequency window free of EPs. We demonstrate that this effect is general, emerging in both the stable and unstable regimes, and occurs from weak modulation strength to low modulations frequencies that could be achieved for various material platforms.

We study spatiotemporal chaos in two-dimensional dense active suspensions using a generalized hydrodynamic model. Increasing activity induces a structural transition marked by the formation of intense vortices and giant number fluctuations at the mesoscale. The flow self-organizes into locally polar-ordered regions coexisting with chaotic domains, producing a bimodal velocity distribution and enhanced correlations. This mixed-state morphology underlies the universal statistical behavior observed beyond a critical activity threshold. Reducing the instability timescale yields similar transitions, showing that both activity and instability act as control parameters for pattern formation. An energy-based order parameter derived from the system’s budget quantifies and unifies these structural transitions across the phase space of activity and instability timescales.

Homologous proteins have similar three-dimensional structures and biological functions that shape their sequences. The resulting coevolution-driven correlations underlie methods from Potts models to alphafold, which infer protein structure and function from sequences. Using a minimal model, we show that fluctuating selection strength and the onset of new selection pressures improve coevolution-based inference of structural contacts. Our conclusions extend to realistic synthetic data and to the inference of interaction partners. Out-of-equilibrium noise arising from ubiquitous variations in natural selection thus enhances, rather than hinders, the success of inference from protein sequences.

Neutron star mergers provide a unique laboratory for the study of strong-field gravity coupled to quantum chromodynamics in extreme conditions. The frequencies and amplitudes of the resulting gravitational waves encode invaluable information about the merger. Simulations to date have shown that these frequencies lie in the kilohertz range. They have also shown that, if quantum chromodynamics possesses a first-order phase transition at high baryon density, then this is likely to be accessed during the merger dynamics. Here, we show that this would result in the nucleation of superheated and/or supercompressed bubbles whose subsequent dynamics would produce gravitational waves in the megahertz range. We estimate the amplitude of this signal and compare it to the sensitivity of planned future detectors.

The ultrarelativistic (Carrollian) regime of gravity has recently emerged as a fertile framework for exploring holography, non-Lorentzian symmetries, and geometric limit of general relativity. In this Letter, we establish the presence of a nonvanishing torsion within three-dimensional Carrollian gravity by constructing the Carrollian Mielke-Baekler (C-MB) gravity theory in its Chern-Simons formulation, obtained as the ultrarelativistic limit of the relativistic Mielke-Baekler model. The resulting C-MB theory features nonzero temporal torsion and curvature, together with spatial curvature, providing the most general three-dimensional Carrollian gravity model with these properties. Temporal torsion affects nonaffinity of null generators and boundary dynamics. Several known ultrarelativistic gravity theories arise as particular limits of this framework, highlighting its unifying character.

Dirac semimetals provide a new platform for the quantum Hall effect at low magnetic fields. In the presence of strong spin-orbit coupling, a spin-split Landau level is expected to enhance the bulk quasiparticle excitation. Here we report NMR spectroscopy that site selectively probes dynamic spin susceptibility on the magnetic semimetal ${\mathrm{BaMnBi}}_2$. We find that spontaneous staggered fields from antiferromagnetic Mn moments are completely canceled at the Bi layer hosting Dirac fermions. The nuclear spin-lattice relaxation rate $1/T_1$ follows the cubic temperature dependence down to low temperatures under the in-plane field, manifesting the chemical potential close to the Dirac point. $1/T_1$ becomes constant below 20 K under the out-of-plane field, where the well-separated Laudau level appears. The strong anisotropy of $1/T_1$ exceeding 100 suggests spin-split Landau levels in the quantum Hall regime.