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.

One-dimensional (1D) structures provide a unique platform to study the correlated quantum interactions and phase transitions such as unconventional magnetism and superconducting states. Here, we report that iron chalcogenide K_{3}Fe_{2}Se_{4} exhibits an unusual block-type canted antiferromagnetic (AFM) order with a clear single chain quasi-1D structure, which is structurally different from the two-leg ladder BaFe_{2}Se_{3}, through both experimental measurements and density matrix renormalization group (DMRG) calculations. The narrow bandgap semiconductor K_{3}Fe_{2}Se_{4} has a quasi-1D edge-shared FeSe_{4} tetrahedra chain structure and orders antiferromagnetically below 110 K. The magnetic moments couple antiferromagnetically along the quasi-1D chain direction of the b axis and form an up-down-down-up (↑-↓-↓-↑)-like spin structure with a commensurate propagation vector k=(0,0,0), where block-type spin ↑-↑ or ↓-↓ coupling are between the longer Fe-Fe bonds of the quasi-1D chain. DMRG results show that block antiferromagnetic state is stable in K_{3}Fe_{2}Se_{4} and reveal that the block-ordered arrangement of Fe^{2.5+} ions spins arise from the competition between ferromagnetic and AFM interaction in the presence of strong electronic correlation. Our research results not only report the discovery of a clear block-type canted antiferromagnetic structure in a real quasi-1D chain material but also provide a theoretical approach to understand the block-type antiferromagnetism in quasi-1D iron chalcogenides.

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.

The superconducting transition temperature T_{c} at KTaO_{3}-based oxide interfaces exhibits a dramatic dependence on crystallographic orientation, yet a unifying mechanism remains elusive. Here, we report a linear scaling between T_{c} and a single geometric parameter-the angle θ between the (hkl) plane and the (100) plane-across ten different orientations of amorphous-LaAlO_{3}/KTaO_{3} interfaces. Except for (100), all orientations exhibit two-dimensional superconductivity, with transition temperatures T_{c} ranging from ∼0.12 to 2.1 K. This linear θ-T_{c} scaling is robust against variations in growth temperature, device geometry, and transport configuration. By establishing the geometric orientation angle as a robust empirical scaling parameter for the superconducting transition, our results set a critical phenomenological benchmark for future microscopic theories of superconductivity in KTaO_{3}-based systems.

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} 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.

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-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-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-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.

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.

While experimental evidence for spacetime supersymmetry (SUSY) in particle physics remains elusive, condensed matter systems offer a promising arena for its emergence at quantum critical points (QCPs). Although there have been a variety of proposals for emergent SUSY at symmetry-breaking QCPs, the emergence of SUSY at fractionalized QCPs remains largely unexplored. Here, we demonstrate emergent spacetime SUSY at a fractionalized QCP in the Kitaev honeycomb model with Su-Schrieffer-Heeger (SSH) spin-phonon coupling. Specifically, through numerical computations and analytical analysis, we show that the anisotropic SSH-Kitaev model hosts a fractionalized QCP between a Dirac spin liquid and an incommensurate or commensurate valence-bond-solid phase coexisting with Z_{2} topological order. A low-energy field theory incorporating phonon quantum fluctuations reveals that this fractionalized QCP features an emergent N=2 spacetime SUSY. We further discuss their universal experimental signatures in thermal transport and viscosity, highlighting the concrete lattice realization of emergent SUSY at a fractionalized QCP in 2D.

We provide a new formulation of time-dependent density functional theory (TDDFT) based on the geometric structure of the set of states constrained to have a fixed density. Orbital-free TDDFT is formulated using a hydrodynamics equation involving a new density-to-current functional map. In the corresponding Kohn-Sham equation, the density is reproduced using a nonlocal operator. Finally, we present numerical simulations for one-dimensional soft-Coulomb systems.

As in thermodynamics, the celebrated first law of black hole mechanics relates infinitesimal changes in the properties of nearby equilibrium states of black holes (without reference to any physical process that causes the transition). Using dynamical horizon segments (DHSs), we extend the first law to encompass black holes that can be arbitrarily far from equilibrium. It now refers to finite changes that occur due to physical processes. This extension, together with the generalized second law on DHSs [A. Ashtekar and B. Krishnan, Dynamical horizons and their properties, Phys. Rev. D 68, 104030 (2003)PRVDAQ0556-282110.1103/PhysRevD.68.104030], naturally lead one to identify entropy of dynamical black holes with the area of DHSs.

The frequency structure of the superconducting correlations in cuprates gives insights on the pairing mechanism. Here we present an exhaustive study of this problem in the two-dimensional Hubbard model with cellular dynamical mean-field theory. To this end, we systematically quantify the dependence on doping δ and interaction strength U of the superconducting gap, of the frequency scales where d-wave pairing occurs, and of their relative contribution to pairing. For all values of U and δ, we find pair-forming processes confined to frequencies set by the superexchange interaction and followed by pair-breaking processes, ruling out both pair-forming and pair-breaking processes on the scale of U. This suggests that at high frequencies, the effect of U is eliminated by the d-wave paring, and that at small frequencies, U generates the superexchange interaction that leads to low-frequency pair-forming processes providing the net contribution to pairing.

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.

We present a study of the melting dynamics of a two-phase eutectic solid. In situ, thin-sample experiments using a transparent eutectic alloy and two-dimensional phase field simulations calibrated for the very same alloy are combined to assess pattern formation during directional melting in a temperature gradient. Depending on the melting velocity V_{m} and the spacing λ of the presolidified lamellar microstructure, an unexpectedly rich diversity of melting patterns is observed, with good agreement between experiments and simulations. We unravel the different physical mechanisms leading to this diversity, and establish the scaling behaviors of (i) the penetration of the liquid along the solid-solid interface at large V_{m}, (ii) the thickening of the primary-phase fingers at low V_{m}, and (iii) a period-doubling instability for small λ values. Our Letter provides a fundamental basis for further investigations of eutectic melting, including additive manufacturing during which melting or solidification cycles take place.

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_{FB} and the exciton kinetic energy t_{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_{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 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.

We consider the string-theory-inspired Einstein-Maxwell-Maxwell-dilaton theory and show that we can derive the complete set of thermodynamic quantities of charged black holes without having to construct the black hole solutions. We argue that the technique can be applied more broadly to string theories, providing an accessible method for determining the thermodynamic properties of large classes of black holes for which exact solutions are typically unavailable.