Negative Poisson’s ratio (NPR) is rare in crystalline solids, and its microscopic origin in oxide perovskites remains elusive. Here we use first-principles calculations to investigate the auxetic response of prototypical ferroelectrics ${\mathrm{PbTiO}}_3$ and ${\mathrm{BaTiO}}_3$ (BTO). We show that NPR is governed by local polar ionic displacements, which stabilize cation-anion bonding environment under deformation and can reverse the sign of the Poisson’s ratio. In particular, NPR in both the tetragonal and cubic phases of BTO emerges only in structures exhibiting local Ti off centering along the $⟨111⟩$ directions, whereas the conventional [001]-polarized tetragonal phase and the high-symmetry cubic structure display positive Poisson’s ratios. Our results establish local polarization as the microscopic origin of NPR in ferroelectrics and highlight it as a tunable parameter for designing auxetic functionality in perovskite oxides.

The energy density generated by a vector current is characterized by a single parameter $a_{\mathcal{E}}$ bounded by unitarity to $-1/2\le a_{\mathcal{E}}\le 1$, with extremal values saturated by free theories of different matter content. Through confinement, QCD transmutes fermionic matter into scalars, revealing a nontrivial flow between extremal correlators. We reconstruct this flow using perturbative QCD and chiral perturbation theory. The observable is accessible with currently available experimental data.

Photonic molecules can mimic interactions of atomic energy levels, offering new ways to manipulate cavity eigenstates. Current methods using evanescent coupling of multiple cavities face challenges in scalability, flexibility, and coupling control, especially for complex systems. Here we introduce a new method that uses a single multimode optical ring resonator to create photonic molecules. Our design uses multiple waveguide transverse modes in one resonator, providing flexibility to engineer complex interactions without typical coupling constraints. We demonstrate arbitrary intermode coupling through transmissive mode converters, allowing precise tuning of resonance splitting and intrinsic losses. This approach enables selective bright-dark mode pair generation and the exploration of novel photonic phenomena such as exceptional points. This multimode photonic molecule overcomes traditional limitations and offers new possibilities for integrated photonic circuits, optical processing, and studies in non-Hermitian and nonlinear photonics.

The first-passage time (FPT) of a stochastic signal to a threshold is a fundamental observable across physics, biology, and finance. While renewal shot noise is a canonical model for such signals, analytical results for its FPT have remained confined to the Poisson (Markovian) case, even though non-Poisson arrival statistics are common in systems from neuronal spiking to gene expression. Here, we overcome this long-standing limitation by deriving a universal asymptotic formula for the mean FPT $⟨T_b⟩$ to reach level $b$ for renewal shot noise with arbitrary arrival statistics and exponential marks. Our central result is a simple, closed-form expression that exposes the physical mechanism by which temporal correlations in arrivals modulate the baseline Arrhenius law. We show that bursty arrivals introduce universal scaling corrections that markedly accelerate threshold crossings. In turn, nonbursty arrivals remain Arrhenius-like, directly linking temporal burstiness to Arrhenius scaling. Furthermore, we show and confirm numerically that the full FPT distribution becomes exponential at large thresholds, implying that $⟨T_b⟩$ provides a complete asymptotic characterization. Our Letter, enabled by a novel exact expression for the moments of the noise, establishes a general framework for analyzing extreme events in non-Markovian systems with relaxation.

The application of a magnetic field has emerged as an effective method for studying the spin-related effects in the oxygen evolution reaction (OER). However, the presence of spin-unrelated effects under a magnetic field also contributes to the observed OER increment, complicating the identification of spin-related enhancement. This is primarily associated with the intrinsic limitation of the conventional magnetic catalysts that require the continuous application of an external magnetic field to maintain the magnetization. Here, we have developed magnetron-sputtered $\mathrm{Co}/\mathrm{PtCo}$ multilayer catalysts with perpendicular magnetic anisotropy, enabling a stable magnetization state without continuous magnetic fields. The magnetic anisotropy of the multilayers is controlled through the number of repetitions of $\mathrm{Co}/\mathrm{PtCo}$ bilayers. As the bilayer number increases from 2 to 25, the domain size at the demagnetized state gradually reduces to the nanometer scale due to the enhanced magnetostatic energy. Upon premagnetization with out-of-plane magnetic fields, the pure spin-enhanced OER is numerically correlated to the change in domain wall ratios, where the global non-spin-related enhancement is effectively excluded. Such spin-enhanced OER is found to be favored by magnetic anisotropy due to the higher magnetic stability to maintain the magnetization state. This Letter provides a new strategy for achieving stable spin-related OER enhancement by magnetic anisotropy, advancing magnetic-field-free spin electrocatalysts to optimize OER performance.

The distribution of absorption lines in the spectra of distant quasars, called the Lyman-$\alpha$ (Ly-$\alpha$) forest, is a unique probe of cosmology and the intergalactic medium at high redshifts and small scales. The statistical power of ongoing redshift surveys demands precise theoretical tools to model the Ly-$\alpha$ forest. We address this challenge by developing an analytic, perturbative forward model to predict the Ly-$\alpha$ forest at the field level for a given set of cosmological initial conditions. Our model shows a remarkable performance when compared with the Sherwood hydrodynamic simulations: it reproduces the Ly-$\alpha$ forest flux power spectrum, its cross-correlation with dark matter halos, and the one-point probability distribution function of both fields at the percent level down to scales of a few Mpc. Our work provides crucial tools that bridge analytic modeling on large scales with simulations on small scales, enabling field-level inference from Ly-$\alpha$ forest data and simulation-based priors for cosmological analyses. This is especially timely for realizing the full scientific potential of the Ly-$\alpha$ forest measurements by the dark energy spectroscopic instrument.

Recent experiments reported evidence of superconductivity and reentrant integer quantum anomalous Hall (RIQAH) insulator upon doping the ${\nu }_e=2/3$ fractional quantum anomalous Hall states (FQAHs) in twisted ${\mathrm{MoTe}}_2$, separated by narrow resistive regions. Anyons of an FQAH generally have a finite effective mass and, when described by anyon-flux composite fermions (CFs), experience statistical magnetic fields with a commensurate filling. Here, we show that most of the experimental observations can be explained by invoking the effects of disorder on the Landau-Hofstadter bands of CFs. In particular, by making minimal assumptions about the anyon energetics and dispersion, we show that doping anyons drives plateau transitions of CFs into integer quantum Hall states, which physically corresponds to either a superconductor or to an RIQAH phase. We develop a dictionary that allows us to infer the response in these phases and the critical regions from the knowledge of the response functions of the plateau transitions. In particular, this allows us to relate the superfluid stiffness of the superconductor to the polarizability of CFs. As a first step toward a quantitative understanding, we borrow results from the celebrated integer quantum Hall plateau transitions to make quantitative predictions for the critical behavior of the superfluid stiffness, longitudinal and Hall conductivity, and response to out-of-plane magnetic field, all of which agree reasonably well with the experimental observations. Our results provide strong support for anyon superconductivity being the mechanism for the observed superconductor in the vicinity of the ${\nu }_e=2/3$ FQAH insulator.

Excitonic band structure is critical for investigating exciton dynamics. Theoretically, quantum effects from exchange scattering between electron-hole pairs significantly modulate exciton dispersion. Here, we report the direct observation of dimensionality-dependent exciton dispersion in a single-band Mott insulator ${\mathrm{Nb}}_3{\mathrm{Cl}}_8$ through high-resolution electron energy loss spectroscopy. In the high-temperature phase, the exciton in ${\mathrm{Nb}}_3{\mathrm{Cl}}_8$ hosts an exceptionally large binding energy, and exhibits clear quasi-two-dimensional massless linear dispersion. In contrast, in the low-temperature phase, the exciton splits into two bands, both displaying three-dimensional parabolic dispersion. These dramatic changes in the exciton dispersion stem from the dimensional mutation driven by a substantial enhancement of interlayer coupling across the phase transition. This Letter provides a clear and typical example of how exciton behavior evolves with dimensionality.

Understanding the folding mechanisms of biomolecules, such as proteins and nucleic acids, requires probing time-dependent changes of conformations, including secondary and tertiary structure formation. All these mechanism-relevant structural transitions, typically seen as coarse-grained descriptions in molecular dynamics simulations, occur in the tiny fraction of a molecular trajectory called the transition path (TP). However, TPs have been inaccessible for most proteins due to the limited time resolution of single-molecule techniques. Here, we measure the TP times of eight two-state single-domain proteins in aqueous solution using nanophotonics-enhanced single-molecule fluorescence spectroscopy. We found that the TP times are extremely short, ranging from 0.7 to $4\mathrm{\mu }\mathrm{s}$, and insensitive to most protein properties. Surprisingly, however, the extracted diffusion coefficient at the free energy barrier on the number of native contacts coordinate increases with protein length. This facilitation of diffusion in larger proteins is explained by increased cooperative native contact formation during folding, which reduces the roughness of the energy landscape. Our results reveal that evolutionary optimization of the energy landscape is much more efficient for protein folding than for other biomolecular processes.

Manipulating the frequency and bandwidth of light is crucial in classical and quantum applications including communication, spectroscopy, imaging, and signal processing. Such capabilities also offer potential for interfacing disparate quantum systems in quantum networking and for quantum information processing. We experimentally demonstrate deterministic, broadband frequency control of heralded telecom-band single photons via cross-phase modulation in a short length of single-mode fiber. An intense, ultrafast pump pulse imposes a transient, intensity-dependent refractive-index gradient which imparts a tunable phase shift on the single photons. We present absolute frequency shifts of up to $+6.42\pm 0.06\mathrm{THz}$ and $-5.82\pm 0.02\mathrm{THz}$, and bandwidth manipulation ranging from a factor of $0.76\pm 0.03$ to $7.1\pm 0.4$ times that of the input. Spectral measurements are acquired with a time-of-flight spectrometer and superconducting nanowire detectors. Our scheme offers a compact and scalable route to spectral routing and bandwidth engineering for ultrafast quantum networking and quantum information processing.

We observe the interlayer $A_{1s}^I$, $A_{2s}^I$, and $B_{1s}^I$ excitons in bilayer ${\mathrm{WSe}}_2$ under applied electric fields using reflectance contrast spectroscopy. Remarkably, these interlayer excitons remain optically bright despite being well separated from symmetry-matched intralayer excitons—a regime where conventional two-level coupling models fail unless unphysically large coupling strengths are assumed. To uncover the origin of this brightening, we perform density functional theory (DFT) calculations and find that the applied electric field distorts the valence-band Bloch states, driving the hole wave function from one layer to the other. This field-driven interlayer hole transfer imparts intralayer character to the interlayer excitons, thereby enhancing their oscillator strength without requiring hybridization with bright intralayer states. Simulations confirm that this mechanism accounts for the major contribution to the observed brightness, with excitonic hybridization playing only a minor role. Our results identify interlayer hole transfer as a key mechanism for brightening interlayer excitons in bilayer transition metal dichalcogenides, especially when inter- and intralayer excitons are energetically well separated.

We characterize monitored quantum dynamics in a solvable model exhibiting a phase transition between a measurement apparatus and a scrambler. We show that approximate decoherent histories emerge in both phases with respect to a coarse-grained extensive observable. However, the apparatus phase, where quantum Darwinism emerges, is distinguished by the nonergodicity of the histories and their correlation with the measured qubit, which selects an ensemble of preferred pointer states. Our results demonstrate a clear distinction between two notions of classicality, decoherent histories, and environment-induced decoherence.

The amplification of magnetic fields is crucial for understanding the observed magnetization of stars and galaxies. Turbulent dynamo is the primary mechanism responsible for that but the understanding of its action in a collapsing environment is still rudimentary and relies on limited numerical experiments. We develop an analytical framework and perform numerical simulations to investigate the behavior of small-scale and large-scale dynamos in a collapsing turbulent cloud. This approach is also applicable to expanding environments and facilitates the application of standard dynamo theory to evolving systems. Using a supercomoving formulation of the magnetohydrodynamic equations, we demonstrate that dynamo action in a collapsing background leads to a superexponential growth of magnetic fields in time, significantly faster than the exponential growth seen in stationary turbulence. The enhancement is mainly due to the increasing eddy turnover rate during the collapse, which boosts the instantaneous growth rate of the dynamo. We also show that the scaling of final saturated magnetic field strength with density robustly exceeds the expectation from considerations of pure flux-freezing. Apart from establishing a formal framework for studying magnetic field evolution in collapsing (or expanding) turbulent plasmas, these findings suggest that during star and galaxy formation magnetic fields can become dynamically relevant much earlier than previously thought.

The photoelectric feedback processes leading to growth of relativistic runaway electron avalanches are believed to be responsible for extreme fluxes of $\gamma$ rays produced from very compact regions of space with dimensions on the order of a hundred meters in association with lightning activity in the Earth’s natural environment [V. P. Pasko et al., Photoelectric effect in air explains lightning initiation and terrestrial $\gamma$ ray flashes, J. Geophys. Res. 130, e2025JD043897 (2025)]. Here, we demonstrate for the first time that the same photoelectric feedback discharges can be realized on centimeter scales in common solid state dielectric materials, like quartz, acrylic, and bismuth germanate. These discharges can serve as new sources of high energy x-ray radiation.

We report pressure-induced superconductivity in the spinel ${\text{CuIr}}_2{\mathrm{S}}_4$ with a transition temperature ($T_{\mathrm{c}}$) reaching 18.2 K, establishing a new record for this class of materials and surpassing the decades-old limit of 13.7 K. Our electrical transport and synchrotron x-ray diffraction studies up to 224 GPa reveal the emergence of two distinct superconducting phases from a charge-ordered insulating state. The first phase (SC-I) appears around 18 GPa, and forms a dome-shaped superconducting region in which the resistivity exhibits a pronounced, field- and current-sensitive drop without reaching strict zero above our base temperature. Above 111.8 GPa, a second, lower-$T_{\mathrm{c}}$ phase (SC-II) emerges and coexists with SC-I over a broad pressure range, and SC-II ultimately develops a true zero-resistance state above 122.2 GPa. These superconducting phases are intimately linked to a cascade of structural transitions that systematically distort the frustrated pyrochlore lattice of Ir atoms. Our results expand the potential for superconductivity in spinels and demonstrate a pathway to high-$T_{\mathrm{c}}$ pairing directly from a correlated insulating state driven by lattice tuning.

Quantum oscillations in electrical transport have long served as a powerful probe of fundamental Fermi surface physics. To date, however, such studies have been restricted to linear electrical transport. This letter presents the experimental observation of quantum oscillations in nonlinear electrical transport and, more importantly, demonstrates their ability to uncover key features of the Fermi surface that lie beyond the reach of linear-transport quantum-oscillation techniques. Using $\alpha \text{−}\mathrm{Sn}$, a topological Dirac semimetal known to support both linear and nonlinear transport, this study shows that quantum oscillations of nonlinear resistance are highly sensitive to both the geometry and spin texture of the Fermi contour—features to which linear counterparts are insensitive. Further, nonlinear-transport oscillations exhibit markedly distinct dependencies on magnetic field and temperature compared to their linear analogs. These findings establish nonlinear-transport quantum oscillations as a transformative tool for exploring Fermi surface physics, opening new avenues for revealing hidden Fermi surface properties in known materials and discovering new exotic electronic states and phases.

Anderson localization is anticipated to play a pivotal role in the manifestation of superconducting phases, optimal thermoelectric properties, and the quantum anomalous Hall effect. Dimensionality plays a central role in the physics of Anderson localization. Previous studies of localization in 2D conductors have relied on thin metallic films produced by vapor deposition, but challenges such as domain size effects, grain boundaries, and strain continue to complicate interpretation. Here, we overcome these challenges by investigating localization physics in ${\mathrm{Pd}}_5{\mathrm{AlI}}_2$, a van der Waals metal that can be exfoliated to the 2D limit. Using scanning tunneling spectroscopy, we demonstrate Anderson localization of electrons in monolayer ${\mathrm{Pd}}_5{\mathrm{AlI}}_2$ from the presence of a Coulomb gap at the Fermi level and a unique density of state distribution characteristic of wave function localization. Moreover, we show evidence of phonon localization in ${\mathrm{Pd}}_5{\mathrm{AlI}}_2$ from the layer-dependent broadening and softening of phonon modes. These signatures of electron and phonon localization, absent in multilayer samples, provide spectroscopic evidence for the theoretical predictions that localization is enhanced at reduced dimensionality.

Atmospheric rivers (ARs) are essential components of the global hydrological cycle, with profound implications for water resources, extreme weather events, and climate dynamics. Yet, the statistical organization and underlying physical mechanisms of AR intensity and evolution remain poorly understood. Here we apply methods from statistical physics to analyze the full life cycle of ARs and identify universal signatures of self-organized criticality. We demonstrate that AR morphology exhibits nontrivial fractal geometry, while AR event sizes—quantified via integrated water vapor transport—follow robust power-law distributions, displaying finite-size scaling. To interpret these emergent behaviors, we develop a moisture avalanche model that reproduces the observed scaling laws and links them to threshold-driven moisture transport and precipitation dissipation. These scaling properties persist under warming scenarios, suggesting that ARs operate near a critical state as emergent, self-regulating systems. Concurrently, we observe a systematic poleward migration and intensification of ARs, driven by thermodynamic amplification and dynamical reorganization. Our findings establish a statistical physics framework for ARs, connecting critical phenomena to the spatiotemporal structure of extreme events in a warming climate.

Lattice vibrations can carry angular momentum and magnetic moments under broken inversion or time-reversal symmetry, forming so-called chiral phonons. While such excitations have been explored in nonmagnetic systems via optical probes, their direct detection in magnetic materials and coupling to spin excitations remain largely unexplored. Here, using neutron spectroscopy, sensitive to both nuclear and magnetic scattering, we reveal the magnetic signature of chiral phonons in ferrimagnetic ${\mathrm{Fe}}_{1.75}{\mathrm{Zn}}_{0.25}{\mathrm{Mo}}_3{\mathrm{O}}_8$ with Curie temperature $T_{\mathrm{C}}\sim 49\mathrm{K}$. Below $T_{\mathrm{C}}$, we observe enhanced magnetic scattering of phonons at small momenta, arising from strong magnon-phonon coupling. In addition, out-of-plane intensity modulation, phonon mode splitting, and field-induced Zeeman shifts are observed, all closely associated with the ferrimagnetic order. These features vanish above $T_{\mathrm{C}}$, where phonon spectra are dominated by nuclear scattering. These observations demonstrate the existence of chiral phonons carrying substantial magnetic moments that directly contribute to magnetic scattering, and establish neutron spectroscopy as a powerful, momentum-resolved probe of their magnetic character.

Temperature-controlled droplet shape transformations have been extensively studied, uncovering the mechanism of convex liquid polyhedron formation but failing to account for concave edges. Here, we reveal interfacially frozen metastable droplets with hexagram projections and concave edges. We combine macroscopic experiments, numerical simulations, and an analytical geometric model, elucidating the mechanism of these phenomena: previously unreported, mobile-fold nano-origami. Our findings open new avenues in self-assembly of complex faceted liquid and solid nanostructures for nanotechnology applications.