Transition-metal dichalcogenides (TMDs) uniquely combine topological electronic states realized without external magnetic fields with a strong optical response arising from long-lived excitons. Motivated by this confluence, we investigate an interacting fermion-boson system formed by coupling an exciton to a quasihole of a fractional Chern insulator (FCI) at filling fraction $1/3$. We introduce a kagome-lattice fermion-boson model hosting an electronic FCI and a mobile exciton whose dispersion is tunable from a parabolic band to a flat band. Using exact diagonalization, we demonstrate the emergence of exciton-quasihole bound states controlled by the repulsive electron-exciton interaction $V_{\mathrm{FB}}$ and the exciton kinetic energy $t_{\mathrm{B}}$. These states appear as low-lying levels in the fermion-boson spectrum, well separated from the scattering continuum, and arise despite repulsive interactions due to a residual attraction to the local charge depletion associated with a quasihole. Reducing $t_{\mathrm{B}}$ enhances this effect by favoring interaction-dominated binding. Our results provide a model description of moiré TMD heterostructures, including fractional Chern insulating twisted bilayer ${\mathrm{MoTe}}_2$ proximitized by excitonic TMD heterobilayers, where we estimate exciton-quasihole binding energy scales of 0.8–1.2 meV, placing these effects within reach of photoluminescence spectroscopy.

Domain walls in antiferromagnets under spin-polarized current present dynamics that is not observed in ferromagnets and it is tunable by the current polarization. Propagating walls are obtained for an in-plane polarization and precessional dynamics is obtained for perpendicular polarization. We obtain the wall velocity by a perturbation method for low velocities, and the wall profile is found to lack a definite parity by perturbation and asymptotic methods. Oscillatory motion of domain walls is obtained for spin polarization that has both perpendicular and in-plane components, and it is found that this comes in two flavors.

Spatiotemporal vortices are polychromatic modes that intertwine orbital angular momentum in space and time. Here, we introduce a new class of such vortices, “spatiotemporal plasmonic vortices,” carrying nontrivial topological spin textures. They are generated by chronotopic interference of temporally delayed plasmonic eigenvortices, where a $\pi$-phase dislocation in the space-frequency domain maps into a $2\pi$ spiraling phase in space-time, with the resulting focus-defocus dynamics emulating U(1) gauge transitions. Using interferometric time-resolved photoemission electron microscopy, we directly image their nanometer-attosecond evolution and control vortex number and position. Quantum-path analysis of coherent two-photon photoemission processes reveals the nonlinear plasmonic polarization fields and angular-momentum conservation, establishing spatiotemporal plasmonic vortices as a platform for probing spatiotemporally structured quantum matter.

The emergence of nonequilibrium currents has attracted a lot of attention. The “ratchet principle” identifies the violation of any form of parity and time-reversal symmetries as the necessary conditions for the emergence of such currents. Here we study active and passive systems with asymmetric spatially varying fluctuation sources that nevertheless remain flux free. For non-interacting systems, we show that a hidden time-reversal symmetry forbids the emergence of steady currents. At higher densities, pairwise forces break this symmetry but an emergent conservation law for the momentum field may nevertheless prevent steady currents. We show how the presence of this conservation law can be tested analytically and characterize the onset of ratchet currents in its absence. Our results show that the ratchet principle should be refined to also preclude bulk momentum conservation.

We point out that dark matter (DM) can illuminate planetary skies via ultraviolet airglow. Dark matter annihilation products can excite molecular hydrogen, which then deexcites to produce ultraviolet emission in the Lyman and Werner bands. We search for this new effect by analyzing nightside ultraviolet radiation data from Voyager and New Horizons flybys of Neptune, Uranus, Saturn, and Jupiter. We set new constraints on the dark matter-nucleon scattering cross section for DM above the electron mass; these extend down to ${10}^{-40}{\mathrm{cm}}^2$ for DM masses around 1 GeV when most of the energy is deposited in the atmosphere. We highlight that future ultraviolet airglow measurements of Solar System planets or other worlds provide a new dark matter discovery avenue.

We numerically solve the conjectured quantum spectral curve for strings on ${\mathrm{AdS}}_3\times {\mathrm{S}}^3\times {\mathrm{T}}^4$ with Ramond-Ramond charge from weak to strong coupling. At strong coupling, the spectrum organizes into flat-space string mass levels with universal square-root scaling in the string tension at leading order, and additional Kaluza-Klein fine-splitting at subleading order. At weak coupling, the energies are determined by a nearest-neighbor Bethe Ansatz, with universal subleading corrections that are suppressed at large volume.

A number of intriguing phenomena, including exciton condensation, orbital ordering, and emergence of chirality, have been proposed to accompany charge-density-wave (CDW) formation in the layered transition metal dichalcogenide $1T\text{−}{\mathrm{TiSe}}_2$. Explaining these effects relies on knowledge of the atomic displacement pattern underlying the CDW, yet structural proposals based on spatially averaging bulk crystal diffraction and surface-dependent scanning tunneling microscopy have remained inconsistent. Here, we revisit the CDW superlattice structure of $1T\text{−}{\mathrm{TiSe}}_2$ with selected-area electron diffraction, a bulk-sensitive probe capable of capturing submicrometer spatial variations while maintaining high momentum resolution. We observed superlattice peak extinction rules that are incompatible with previously reported atomic displacement patterns, and we found two categories of CDW phases characterized by distinct interlayer orderings. Our analysis identifies a set of possible superlattice structures consistent with the extinction rules, all featuring a one-dimensional displacement pattern for each atomic type and possessing a large number of nearly degenerate CDW domains. These findings shed light on the longstanding discrepancy in the low-temperature space group of $1T\text{−}{\mathrm{TiSe}}_2$ and provide a new basis for understanding the gyrotropic electronic order and metastability in this material. Our results further underscore the importance of bulk-sensitive mesoscopic techniques in investigating materials that host unconventional superlattices.

The antiferroaxial state is emerging as an important ferroic order in condensed matter systems. Here, we establish antiferroaxial altermagnetism as a broadly prevalent, generic, and microscopically grounded multiferroic mechanism, in which antiferroaxial counterrotating distortions both induce altermagnetism and enable its deterministic and reversible switching. Within a unified Landau-theory and symmetry framework, we identify a symmetry-allowed trilinear invariant coupling the antiferroaxial order, the Néel vector, and the altermagnetic order and derive general symmetry criteria for its occurrence. This coupling locks the induced altermagnetism to the antiferroaxial order, so that reversing the latter reverses the spin splitting and associated time-reversal-odd responses, such as anomalous Hall conductivity. We provide a practical spin-group dictionary mapping Néel-vector representations to the resulting $d$-, $g$-, and $i$-wave antiferroaxial altermagnetism, validate the mechanism with ligand-rotation tight-binding models and first-principles calculations, and identify many candidate materials by screening the MAGNDATA and C2DB databases. Our results elevate antiferroaxiality to a universal ferroic control knob for structurally programmable altermagnetic spintronics.

The dynamical control over electronic properties represents a key area of research in condensed-matter physics. Here, we demonstrate all-optical control of carrier-strain-mediated giant enhancement of spin splitting (100 meV) in a chiral 2D perovskite. Ultrafast circular dichroism measurements and ab initio calculations reveal that anisotropic strain from confined photoexcited excitons enhances spin splitting, thereby creating a spin-dependent hot-carrier relaxation pathway and tripling hot-carrier lifetimes. Our findings establish a versatile optical strategy for coherent spin manipulation and open avenues for developing spin-based hot-carrier devices.

Cell shape changes are largely controlled by the actin cytoskeleton, a dynamic filament network beneath the plasma membrane. Several cell types can form extended freestanding protrusions not supported by an extracellular substrate or matrix, and regulated by proteins sensitive to the cell membrane curvature that modulate cytoskeletal dynamics. To gain insight into this process, we develop a theoretical model for the mechanics of a freestanding viscous actin network growing on a corrugated membrane. The model couples the dynamics of the viscous active gel with membrane deformation and the recruitment of curvature-sensitive actin nucleators. We show that an actin layer polymerising uniformly on the membrane always exerts a stabilizing effect that reduces membrane deformation. However, curvature-sensitive actin nucleator proteins can render the membrane linearly unstable, depending on the interplay between membrane and actin dynamics, giving rise to spontaneous membrane deformation which could initiate extended freestanding cellular protrusion.

Establishing a notion of the quantum state that applies consistently across space and time could be a crucial step toward formulating a relativistic quantum theory. We give an operational meaning to multipartite quantum states over arbitrary regions in spacetime through a causally agnostic measurement, a measurement scheme that can be consistently implemented independently of the causal relation between the regions. We prove that such measurements can always be implemented with interferometry, also known as the scattering circuit technique, wherein the conventional density operator, the recently developed quantum state over time (QSOT), and the process matrix formalisms smoothly merge. This framework allows for a systematic study of mixed states in the temporal setting, which turn out to be crucial for modeling quantum non-Markovianity. Based on this, we demonstrate that two different ensembles of quantum dynamics can be represented by the same QSOT, indicating that they cannot be distinguished through interferometry. Moreover, our formalism reveals a new type of spatiotemporal correlation between two quantum dynamics that originates from synchronized propagation in time under time-reversal symmetry. We show that quantum systems with such correlation can be utilized as a reference frame to distinguish certain dynamics indistinguishable under time-reversal symmetry.

Recent advances in microwave shielding have increased the stability and control of large numbers of polar molecules, allowing for the first realization of a molecular Bose-Einstein condensate. Remarkably, it was also recently realized that shielded polar molecules exhibit an $\mathrm{SU}(N)$ symmetry among their hyperfine states, opening the door to $\mathrm{SU}(N)$ systems with larger $N$, bosonic particle statistics, and tunable interactions—both repulsive and attractive. Motivated by these results, we have studied the SU(3) attractive Fermi-Hubbard model (FHM) on a square lattice. Using the determinant quantum Monte Carlo (DQMC) method, we explore the finite temperature phase diagram and provide evidence for three distinct regions—a three-component Fermi liquid (FL) region, a “trion” liquid (TL) region, and an ordered charge density wave (CDW) phase. The CDW phase is stable at finite temperature [in contrast to the SU(2) CDW], while the FL to TL crossover appears to point to a quantum phase transition at zero temperature. Our method extends straightforwardly to larger $N$ and is sign problem free for even values of $N$. With these results, we demonstrate the potential physics enabled by using polar molecules as a quantum simulation platform for the attractive $\mathrm{SU}(N)$ FHM.

We propose a renormalization group flow equation for a functional that generates $S$-matrix elements and which captures similarities to the well-known Wetterich and Polchinski equations. While the latter ones, respectively, involve the effective action and Schwinger functional, which are genuine off-shell objects, the presented flow equation has the advantage of working more directly with observables, i.e., scattering amplitudes. Compared to the Wetterich equation, our flow equation also greatly simplifies the notion of going on shell, in the sense of satisfying the quantum equations of motion. In addition, unlike the Wetterich equation, it is polynomial and does not require a Hessian inversion. The approach is a promising direction for nonperturbative quantum field theories, allowing one to work more directly with scattering amplitudes.

Reservoir engineering enables unidirectional energy and signal flow. We establish squeezing-induced symmetry breaking between two cavities as a guiding principle for exponentially amplifying reservoir-mediated nonreciprocity. Rather than a simple scaling of the coupling, this mechanism strategically redistributes the squeezing resources to relax experimental requirements, as single-cavity squeezing alone demands a much larger squeezing strength. Moreover, reservoir squeezing does not alter the system symmetry but reshapes the noise correlations and thereby changes the system dynamics. The proposed mechanism improves the performance of the quantum battery by several orders of magnitude, including stored energy, charging power, and ergotropy, with the analytical expressions provided. Extending to the optical isolation, we observe a second-order exponential enhancement of the output signal. Our results open a new avenue for nonreciprocal quantum information processing and nonreciprocal quantum device design.

Chiral objects typically exhibit a different extinction for the two circular polarizations of light. Researchers often detect the chirality of objects by measuring this extinction difference employing circular dichroism spectroscopy. In this Letter, we present a new spectroscopy technique for detecting the chirality of dipolar objects based on measuring the Stokes parameters at any nonforward angle. The chirality measure we introduce effectively eliminates achiral background noise and is independent of both the object’s concentration and the optical path length. Notably, when a solution contains both enantiomers of a chiral object, our method can discern which enantiomer predominates. Furthermore, we demonstrate that the technique is robust and verifiable in situ by measuring the Stokes vector at two different nonforward angles of choice.

We demonstrate thermodynamic irreversibility in the stochastic switching of a coherently driven bistable optical cavity. We present measurements of phase space probability currents evidencing the breaking of detailed balance associated with thermodynamic irreversibility. We also estimate the magnitude of the irreversibility via the relative entropy of up and down switches. Our experimental observations are supported by a theoretical model, illustrating how the magnitude of the irreversibility of composite systems strongly depends on the interactions between subsystems (modes) regardless of their driven-dissipative nature. Our work establishes driven-dissipative optical resonators as a platform for experiments in stochastic thermodynamics, which could in turn help answer the long-standing question of what is the minimum energy required for an optical switch.

We study phase-separating fluid mixtures as they demix in the presence of chemical reactions that maintain them away from thermodynamic equilibrium. We show that in such chemically active emulsions the interplay of chemical reactions, phase separation, and hydrodynamics effects complex self-organization and pattern formation that can give rise to spatiotemporal chaos. This chaotic dynamics, unlike in classical turbulence, is not due to fluid inertia—we analyze the system in the Stokes flow regime—and it is different from the turbulence of active nematics at low Reynolds number, for our fluid mixtures lack any orientational order. To explore the generic features of nonlinear dynamics in our system, we derive amplitude equations which we find to be identical to those obtained for Rayleigh-Benard convection with mean flow and stress-free conditions at the top and bottom plates. Chemically active emulsions possessing no internal order, we thus establish, can exhibit chaoticity that is driven by interfacial stresses in the fluid mixture.