Topological physics has garnered attention across various fields, emphasizing topologically protected modes renowned for their robustness against disorders. Recent advancements have expanded from conservative wave systems to diffusion systems with dissipative interactions. However, the transition region between wave and diffusion dynamics remains scarce, primarily due to the complexities involved in coupling modulation. Here, we develop a universal coupling control scheme via reservoir engineering, achieving conservative, dissipative, and mixed topologies in an optical waveguide array. Contrary to the belief that topological modes are disorder resistant, we found that topological dissipative modes are highly sensitive to initial excitations and noise. This sensitivity is due to their residence within the complex band gap, facilitating the excitation and preservation of bulk modes with lower loss. We also propose a method to control the degree of topological robustness and even stabilize these sensitive topological states by selectively managing dissipative potentials. Our Letter offers new insights into the dissipative dynamics of topological states, paving the way for wave coherent manipulation and diffusion transport on photonic chips.

Avalanches are abundant abrupt events that occur during various physical processes, where the material transitions between equilibrium states through complex dynamics. Relaxation’s dynamics are simpler and milder compared to avalanches, typically following a well-defined kinetic law. Here, we reveal the elemental differences between avalanches and relaxations during deformation twinning in magnesium in terms of their rate and duration. At the same time, we find that each avalanche is followed by relaxation with an almost identical magnitude. An avalanche occurs at the $\mathrm{\mu }\mathrm{s}$ timescale and corresponds to a twin nucleation while relaxation occurs at the ms timescale and corresponds to twin growth. Our results indicate that the local volumes twinned during these two coupled processes are nearly identical. This implies a simple geometrical relation between twin nucleation and subsequent twin growth, shedding light on the basic mechanisms during the early stages of twinning.

The late-time equilibrium behavior of generic interacting models is determined by the coupled hydrodynamic equations associated with the globally conserved quantities. In the presence of an external time-dependent drive, nonintegrable systems typically thermalize to an effectively infinite-temperature state, losing all memory of their initial states. However, in the presence of a large time-periodic Floquet drive, there exist special points in phase space where the strongly interacting system develops approximate emergent conservation laws. Here, we present results for an exactly solvable model of two coupled chaotic quantum dots with multiple orbitals interacting via random two- and four-fermion interactions in the presence of a Floquet drive. We analyze the phenomenology of dynamically generated freezing using a combination of exact diagonalization and field-theoretic analysis in the limit of a large number of electronic orbitals. The model displays universal freezing behavior irrespective of whether the theory is averaged over the disorder configurations or not. We present explicit computations for the growth of many-body chaos and entanglement entropy, which demonstrates the long-lived coherence associated with the interacting degrees of freedom even at late times at the dynamically frozen points. We also compute the slow timescale that controls relaxation away from exact freezing in a high-frequency expansion.

Ensembles that respect symmetries on average exhibit richer topological states than those in pure states with exact symmetries, leading to the concept of average symmetry-protected topological states (ASPTs). The free-fermion counterpart of ASPT is the so-called statistical topological insulator (STI) in disordered ensembles. In this Letter, we demonstrate the existence of an intrinsic STI, which has no clean counterpart. Using a real space construction (topological crystal), we find an axion STI characterized by the average axion angle $\overline{\theta }=\pi$, protected by an average $C_{4}T$ symmetry with $(C_{4}T{)}^4=1$. While the exact $C_{4}T$ symmetry reverses the sign of $\theta$ angle, and hence seems to protect a ${\mathbb{Z}}_2$ classification of $\theta =0,\pi$, we prove that the $\theta =\pi$ state cannot be realized in the clean limit if $(C_{4}T{)}^4=1$. Therefore, the axion STI lacks band insulator correspondence and is thus intrinsic. To illustrate this state, we construct a lattice model and numerically explore its phase diagram, identifying an axion STI phase separated from both band insulators and trivial Anderson insulators by a metallic phase, revealing the intrinsic nature of the STI. We also argue that the intrinsic STI is robust against electron-electron interactions. Our Letter thus provides the first intrinsic crystalline ASPT and its lattice realization.

Twisted bilayer graphene (TBG) features strongly correlated and topological phases due to its flat bands emerging near the magic angle. However, the effects of the non-Hermiticity, arising from the coupling to the environment and dissipation, have remained unexplored. We here develop a simple non-Hermitian (NH) version of twisted bilayer graphene (TBG) by considering relative twisting of two NH graphene monolayers with non-Hermiticity encoded in the imbalance of in-plane nearest-neighbor hopping amplitudes. Remarkably, by generalizing the Bistritzer-MacDonald approach to NH systems, we discover exceptional magic angles where the band structure changes from purely real to purely imaginary thus featuring flat bands with infinite lifetime. Between them, the bands remain flattened, and a Hermitian magic angle emerges at which the imaginary part of energy is maximal, and corresponds to the usual magic angle in nondissipative, purely Hermitian TBG. We propose an optical lattice setup with gain and loss where our theoretical predictions can be verified. These results suggest the robustness of the flat bands in open systems, paving the way for the further studies on the interplay of dissipative effects, electronic topology, and interactions in such NH moiré bands.

Altermagnets are collinear compensated magnets in which the magnetic sublattices are related by rotation rather than translation or inversion. One of the quintessential properties of altermagnets is the presence of split chiral magnon modes. Recently, such modes have been predicted in ${\mathrm{MnF}}_2$. Here, we report inelastic neutron scattering results on an ${\mathrm{MnF}}_2$ single crystal along high-symmetry Brillouin zone paths for which the magnon splitting is expected. Within the resolution of our measurement, we do not observe the predicted splitting. The inelastic spectrum is well modeled using $J_1$, $J_2$, $J_3$ nearest-neighbor exchange interactions with weak uniaxial anisotropy. These interactions have higher symmetry than the crystal lattice, while the interactions predicted to produce the altermagnetic splitting are negligibly small. Therefore, the two magnon modes appear to be degenerate over the entire Brillouin zone and the spin dynamics of ${\mathrm{MnF}}_2$ is indistinguishable from a classical Néel antiferromagnet. Application of a magnetic field causes a Zeeman splitting of the magnon modes close to the $\mathrm{\Gamma }$ point. Even if chiral magnon modes are allowed by altermagnetic symmetry, the splitting in real materials such as ${\mathrm{MnF}}_2$ can be negligibly small.

The origin of frequently observed ultrahigh electro-induced longitudinal strain, ranging from 1% to 26%, remains an open question. While recent studies have associated this phenomenon with bending deformation, the underlying mechanisms and the pronounced thickness dependence of the nominal strain have yet to be fully elucidated. Here, we demonstrate that the bending in piezoelectrics can be induced by a nonzero gradient of $d_{31}$ across thickness direction. A scaling law (${\eta }_{3,\mathrm{nom}}\propto L^2{E}_3{\nabla }_z{d}_{31}/t$) is derived to quantify the size dependence, thereby resolving longstanding ambiguities surrounding reported “giant” electrostrains. Simulations reveal that in standard perovskite piezoceramics, such as ${\mathrm{KNbO}}_3$, a 0.69% concentration of oxygen vacancies can induce a $6.3\mathrm{pC}/\mathrm{N}$ variation in $d_{31}$ by suppressing polarization rotation, being sufficient to produce ultrahigh nominal strain in thin samples. Numerous factors, including gradients in defect concentration, composition, and stress, may lead to sufficient inhomogeneity in the distribution of $d_{31}$, suggesting electrobending may be a widespread phenomenon. This Letter presents a unified framework for understanding electrobending deformation, offering deeper insight into the mechanisms behind abnormally giant electrostrain responses in diverse piezoelectric systems and may encourage new engineering applications.

When a small system is coupled to a bath, it is generally assumed that the state of the bath remains unaffected by the system due to the bath’s large number of degrees of freedom. Here, we show theoretically that this assumption can be easily violated for photonic baths typically used in experiments involving superconducting circuits. We analyze the dynamics of a voltage-biased Josephson junction coupled to a photonic bath, represented as a long Josephson junction chain. Our findings show that the system can reach a nonequilibrium steady state where the photonic degrees of freedom become significantly overheated, leading to a qualitative change in the current-voltage $I–V$ curve. This phenomenon is analogous to the Joule effect observed in electrical conductors, where flowing current can substantially heat up electrons. Recognizing this effect is crucial for the many applications of high-impedance environments in quantum technologies.

The fractional Brownian motion (fBm) is a paradigmatic strongly non-Markovian process with broad applications in various fields. Despite their importance, the properties of the territory covered by a $d$-dimensional fBm have remained elusive so far. Here, we study the visitation dynamics of the fBm by considering the time ${\tau }_n$ required to visit a site, defined as a unit cell of a $d$-dimensional lattice, when $n$ sites have been visited. Relying on scaling arguments, we determine all temporal regimes of the probability distribution function of ${\tau }_n$. These results are confirmed by extensive numerical simulations that employ large deviation Monte Carlo algorithms. Besides these theoretical aspects, our results account for the tracking data of telomeres in the nucleus of mammalian cells, microspheres in an agorose gel, and vacuoles in the amoeba, which are experimental realizations of fBm.

We propose a Green-Kubo-like relation for kinetic energy diffusivity to investigate the interplay between ergodicity and anomalous diffusion. This approach introduces a fluctuation metric for the time-averaged kinetic energy, which holds for scaling velocity correlation functions. We demonstrate that as stationary diffusive systems transition into an effective ergodic phase, their kinetic energy metric converges to a universal law. This finding provides a robust framework for understanding the dynamics of such systems. Applications to protein folding and single-particle tracking illustrate the practical utility of our approach, offering a clear prescription for extracting key physical parameters, such as the friction constant and relaxation time, from finite experimental datasets. Importantly, this method remains effective even when the underlying processes exhibit weak ergodicity breaking or are bounded. Furthermore, we explore the nonergodic transition associated with the aging velocity correlation function observed in granular gases.

Simple active models of matter recapitulate complex biological phenomena. The out-of-equilibrium nature of these models, however, often makes them beyond the reach of first-principle descriptions. This limitation is particularly perplexing when attempting to distinguish between different glass-forming mechanisms. We here consider a minimal active system in various spatial dimensions to identify the processes underlying their sluggish dynamics. Activity is found to markedly impact cage escape processes and critical fluctuations associated with exploring lower-dimensional caging features.

The $\delta N$ formalism is a powerful approach to compute nonlinearly the large-scale evolution of the comoving curvature perturbation $\zeta$. It assumes a set of FLRW patches that evolve independently, but in doing so, all the gradient terms are discarded, which are not negligibly small in models beyond slow roll. In this Letter, we extend the formalism to capture these gradient corrections by encoding them in a homogeneous-spatial-curvature contribution assigned to each FLRW patch. For a concrete example, we apply this formalism to the ultra-slow-roll inflation, and find that it can correctly describe the large-scale evolution of the comoving curvature perturbation from the horizon exit. We also briefly discuss non-Gaussianities in this context.

We show that collisions between particles free falling from infinity and a disk of material plunging off the retrograde innermost stable circular orbit of a near-extremal Kerr black hole is the unique astronomically natural way in which to create a gravitational particle accelerator with center of mass energies at the tens to hundreds of teraelectronvolt range; in other words, a supercollider.

When a column of water drains from a vertical tube, it often leaves behind a trailing film that forms intricate, axisymmetric liquid structures. Using high-speed imaging and first-principles modeling, we investigate the formation and breakup of these fluted films and demonstrate that their diverse morphologies arise from the evolving balance of inertia, surface tension, gravity, and viscous forces. By analyzing the characteristic timescales for film emergence, retraction, and rupture, we classify the observed behaviors into distinct regimes and predict the transitions between them. Our theoretical framework captures the transient velocity and thickness of the film at the tube exit and yields regime boundaries that closely match experimental observations. These results not only explain a deceptively simple fluid dynamic system but also provide insight into film stability, merging, and rupture processes relevant to falling film evaporators, coating flows, and capillary-inertial instabilities across soft matter and multiphase systems.

By employing the formalism of hydrodynamics, we derive novel analytic predictions for the Doppler effect in superfluids with broken Galilean invariance and hosting persistent currents at zero temperature. We consider two scenarios: when Galilean invariance is broken explicitly (by external potentials) and spontaneously, as it happens in a supersolid. In the former case, the presence of a stationary current affects the propagation of sound via an anomalous Doppler term proportional to the density derivative of the superfluid fraction. In supersolids, where, according to Goldstone theorem, distinct sounds of hybrid superfluid and crystal nature can propagate, the Doppler effect can be very different for each sound. Quantitative estimates of the Doppler shifts are obtained for Bose-Einstein condensed atomic gases, described by Gross-Pitaevskii theory. The estimates are obtained both calculating the thermodynamic parameters entering the hydrodynamic results and from full time-dependent simulations.

Electronic and thermal transport properties in two-dimensional (2D) semiconductors have been extensively investigated due to their potential to miniaturize transistors. Microscopically, electron-phonon interactions are considered the dominant momentum relaxation mechanism for electrons that limits carrier mobility beyond cryogenic temperatures. However, when electrons and phonons are considered as a single system, electron-phonon interactions conserve the total momentum and energy, leading to the possibility of low-dissipation transport. In this Letter, we systematically investigate the momentum circulation, in which momentum previously transferred from electrons to phonons (or vice versa) can be pumped back to the original carriers through interactions between nonequilibrium electrons and phonons, and its impact on carrier transport properties in 2D semiconductors with strong electron-phonon interactions. We find that, when strong momentum circulation is taken into account, the total momentum in the coupled electron-phonon system is weakly dissipated, leading to a coupled electron-phonon hydrodynamic transport regime, in which electrons and phonons exhibit a joint drift motion rather than separate diffusive behaviors. In this transport regime, charge transport properties are significantly enhanced. Contrary to previous belief, our results demonstrate that low-dissipation charge transport can occur despite strong electron-phonon interactions when there is effective momentum circulation between electrons and phonons. Our Letter advances fundamental understandings of carrier transport in 2D semiconductors.

Sufficiently clean geometrically frustrated (GF) magnets are the largest class of candidate materials that may host quantum spin liquids (QSLs). Some of them have been shown to exhibit spin-glass freezing, potentially precluding QSLs, at the “hidden energy scale,” which is significantly lower than the microscopic energy scale of spin interactions. Here, we investigate the origin of the hidden energy scale and its relationship to the $f$ ratio, the figure of merit for the degree of frustration in GF magnetic materials. The available experimental and numerical data provide evidence that GF magnets display, universally, two distinct temperature scales in the specific heat, the lowest of which is of the order of the hidden energy scale $T^{*}$. We argue that this scale is determined by nonmagnetic excitations, similar to spin exchanges in chains of spins. The collective entropy of such excitations matches the entropy of the ground states of the Ising model on the same lattice, which provides a way to verify the proposed scenario in experiment. We demonstrate that in the presence of quenched disorder, a broad class of materials exhibits spin-glass freezing at temperatures of order $T^{*}$, in accordance with experimental observations. As $T^{*}$ is a property of the clean GF medium, it leads to a constraint on the $f$ ratio.

We experimentally investigate the statistical properties of a classical analog of quantum entanglement between two Brownian particles connected by an elastic force and maintained at different temperatures through separate heat reservoirs. Uncertainty relations between coordinates and coarse-grained velocity can produce a phenomenon similar to quantum entanglement, where temperature plays the role of Planck’s constant. The theoretical analysis matches the experimental results, confirming that the interconnected particles exhibit Brownian quantum-inspired classical correlation entanglement. This effect arises from a coarse-grained description of Brownian motion and vanishes at a finer resolution. The coarsening scale range is measured too.