Papers

Recent transport measurements on freestanding La$_{0.8}$Sr$_{0.2}$NiO$_2$ membranes revealed a broad superconducting dome extending from ambient pressure to 210 GPa, with an onset transition temperature reaching 74.5 K near 146 GPa. Using first-principles calculations, a pressure-dependent two-orbital model, and self-consistent FLEX calculations combined with the linearized Eliashberg equation, we determine how compression modifies the pairing tendency. Pressure increases the kinetic-energy scale, reduces $U_x/t_1$, strengthens interlayer hybridization, and transfers holes from the La/Sr-derived charge reservoir to the correlated Ni sector. Within the present low-energy description, the increasing kinetic scale and the approach to optimal intermediate coupling account for the initial enhancement of pairing, whereas pressure-induced self-doping into the overdoped regime is primarily responsible for its high-pressure suppression. Despite a pronounced three-dimensionalization of the Fermi surface, the pairing-relevant spin susceptibility remains weakly dependent on $q_z$ and peaked near $(\pi,\pi)$. Consequently, the Ni-$d_{x^2-y^2}$-dominated $d$-wave pairing state remains stable over the calculated pressure range. These results provide a unified microscopic interpretation of both the superconducting dome and its unusual robustness under megabar compression.

Continuous, non-invasive monitoring of the arterial pulse is a clinical priority for cardiovascular disease, the leading cause of global mortality. Flexible piezoelectric electronic skins can transduce the 1-10 kPa pressure wave into a self-powered voltage, but the best-performing piezoceramics are lead-based, and their toxicity is incompatible with skin contact and with tightening RoHS/REACH regulation. Among lead-free alternatives, the BaTiO$3$-based solid solution BZT-BCT reaches $d{33} \approx 620$ pC/N near its tricritical morphotropic phase boundary, rivalling soft PZT while remaining biocompatible. Exploiting this in a wearable confronts a sensitivity-flexibility paradox and three computational walls: the combinatorial explosion of atomic configurations in a disordered solid solution, the band-gap error of affordable density-functional approximations, which corrupts leakage and insulation estimates, and the 0 K nature of standard calculations against a 310 K operating temperature. We review lead-free piezoelectrics, morphotropic-boundary physics and fabricated flexible devices, then argue that equivariant machine-learning interatomic potentials — coupled to a tiered functional hierarchy and finite-temperature lattice dynamics — can survey the full configurational ensemble at body temperature and close the gap to a clinically viable lead-free pulse sensor.

The discovery of high-temperature superconductivity in Ruddlesden-Popper (RP) nickelates has attracted significant attention. Bulk superconductivity emerges under pressure in trilayer nickelates La$_4$Ni$_3$O$_{10-\delta}$ (T$_c$ $\approx$ 30 K) and Pr$_4$Ni$_3$O$_{10-\delta}$ (T$_c$ $\approx$ 40.5 K), where the reduced ionic radius of Pr$^{3+}$ may generate internal chemical pressure and enhance T$_c$. However, synthesizing trilayer RP phases with smaller rare-earth elements (Ln) is extremely challenging. So far, only the La, Pr, and Nd analogues have been synthesized with stable phases in the single rare-earth form. Here we report the first successful high-pressure and high-temperature (HPHT) synthesis of samarium-based compound Sm$_4$Ni$_3$O$_{10-\delta}$. Magnetization and transport measurements consistently confirm a density wave (DW) transition at ~180 K at ambient pressure. Through a careful fitting to the structural data of Sm$_4$Ni$_3$O$_{10-{\delta}}$, it is found that the bond angle of (Ni-O-Ni) associating with the interlayer apical oxygen is much smaller than 180$^{\circ}$, which was assumed to be the key factor for the occurrence of superconductivity. By applying pressures up to 80 GPa, despite partial suppression of insulating behavior and the DW order, but superconductivity is not observed in our present study. Density functional theory calculations suggest that the 3d$_{z^2}$ and 3d$_{x^2-y^2}$ are separated from other t$_{2g}$ orbitals and make a primary contribution to the Fermi surface. The newly synthesized trilayer nickelate Sm$_4$Ni$_3$O$_{10-\delta}$ offers a unique platform for probing the fundamental physics of RP nickelates.

At the water-land interface, amphibious fishes encounter wet flowable substrates made of granular solid-water mixtures, which can stay solid or flow like a fluid. As these substrates become wetter or drier, their yield strength (at which solid-fluid transition occurs) and cohesion (how sticky they are) both change, challenging locomotion. Despite substantial understanding of tetrapod locomotion on flowable substrates (mostly dry sand), we know little about how amphibious fishes cope with wet flowable substrates of various wetness. Here, we studied mudskippers on clay mud of controlled, variable wetness over the range where solid-fluid transition occurs. As mud became wetter, its strength decreased by 100-fold, leading the animal to sink deeper, with larger areas of body and fins contacting mud. By contrast, mud stuck most easily at intermediate wetness. The increased sinkage and contact and stickiness change caused more mud to stick to and pull against the animal on wetter mud. We also tested dry mud, which stuck to animal fins as its mucus dried. Despite these challenges, the mudskipper predominately used a conserved crutching gait on all except the wettest mud tested, with a modest performance reduction. When normal crutching became less effective, the animal assisted it with tail thrusting, by bending and straightening it to push downward and backward to generate additional thrust and lift, or even thrusting the tail to jump. These observations suggest that mudskipper's crutching motor program is well adapted to its native muddy substrates but inflexible, with most novelty in tail use.

Animals and robots encounter mud at the water-land interface. Like sand, mud can stay solid or flow like a fluid. Unlike sand, the yield strength of mud at which solid-fluid transitions occur depends on not only the amount of solid relative to fluid (water in mud, air in dry sand), but also how much coarse grains and fine clay are within the solid. Despite understanding of locomotion on/within dry sand dominated by coarse grains with repulsive normal forces and friction, little is known for mud dominated by fine clay with strong cohesion. Here, we developed methods to prepare uniform mud of controlled, variable yield strength and characterize and track its drift from water evaporation. Compared to other flowable substrates, mud strength measured by upward force during penetration is weaker and can vary more, and mud sticks more during extraction to pull downward, making it more challenging for locomotion.

We show that for any potential with a discrete energy spectrum, the well-known interpolation between ideal boson and fermion partition functions at discrete values of $\xi=-1/m$ yielded zero temperature ground state energies corresponding to $m$ fermions occupying a single quantum state. The grand canonical partition function in this case can be a result from genuine parastatistics.

High-temperature superconductivity has been found in bilayer Ruddlesden-Popper (RP) nickelates in bulk samples under high pressure, or in thin films via compressive strain. In the superconducting state, a tetragonal structure with a straight Ni-O-Ni bond along c-axis has been commonly observed, together with the suppression or diminishing of the density-wave orders. Therefore, it remains an open question whether these factors are sufficient for achieving superconductivity at ambient pressure. Here we report the first successful synthesis of heavily Sr-doped La$_{2}$SrNi$_{2}$O$_{7-{\delta}}$ under high-pressure and high-temperature (HPHT) conditions with a flux method. X-ray diffraction and scanning transmission electron microscopy (STEM) confirm that the material adopts a tetragonal (I4/mmm) structure with an 180$^{\circ}$ Ni-O-Ni bond angle along c-axis. Resistance measurements reveal metallic behavior with a low-temperature upturn and no density-wave features are observed. However, neither pressure nor oxygen variation induces superconductivity. Density functional theory calculations indicate that the holes introduced by Sr doping are predominantly doped into the Ni-3d$_{z^2}$ orbital, leading to the appearance of a very large ${\gamma}$ pocket on the Fermi surface at ambient pressure and significantly reducing the occupation of the Ni-3d$_{z^2 }$ orbital. Combining the experimental observations with theoretical calculations, we attribute the absence of superconductivity to the serious deviation from the half-filling state of the Ni-3d$_{z^2 }$ band, which is crucial for the interlayer antiferromagnetic interaction and thus for pairing. Our work unravels important issues for achieving superconductivity in bilayer nickelate system.

Materials exhibiting strongly anisotropic lattice thermal conductivity are desirable for thermal-management applications, yet such behavior is commonly associated with layered or quasi-one-dimensional van der Waals crystals and highly anisotropic elastic properties. Here, we investigate lattice thermal transport in the hexagonal perovskites Cs$BX_3$ ($B=$ Mg, Cd; $X=$ Cl, Br, I) using first-principles calculations. At 300~K, the calculated in-plane and out-of-plane lattice thermal conductivities range from 0.13–0.83 and 0.34–6.26~Wm$^{-1}$K$^{-1}$, respectively, corresponding to anisotropy ratios of 2.6–7.5. This pronounced anisotropy is remarkable given the relatively modest elastic anisotropy, characterized by $C_{33}/C_{11}$ = 0.994–1.842. Our analysis reveals that medium-frequency optical phonons provide an efficient out-of-plane heat-transport channel, contrary to the conventional picture in which heat transport is dominated by acoustic phonons. These findings identify face-sharing octahedral frameworks as a promising platform for engineering strong thermal-conductivity anisotropy in mechanically near-isotropic, non–van der Waals crystals.

High-harmonic generation (HHG) provides a coherent ultrashort-pulse light source in the extreme- ultraviolet (XUV) region and has potential applications in time-resolved spectroscopy and materials characterization. In this study, we constructed an HHG system using a Yb:KGW laser system (PHAROS, Light Conversion) as the driving source and Ar gas as the nonlinear medium. High-order harmonics were observed up to a photon energy of 70.6 eV, corresponding to the 59th harmonic order. As an application of the developed XUV source, we measured the transmission of a Mg thin film and a Si3N4 membrane. In addition, the surface chemical state of the Mg thin film was characterized by X-ray photoelectron spectroscopy (XPS), and the results were compared with the transmission measured using the HHG source. This comparison was used to examine the relationship between the surface condition, including surface oxidation, and the XUV transmission of the Mg thin film. These results demonstrate the applicability of the developed Ar-based HHG source to the characterization of thin-film transmission in the XUV spectral region.

In a recent Letter, Sun et al. report photoemission spectroscopy measurements on the four-layer cuprate (Cu,C)Ba2Ca3Cu4O11 (CuC-1234) in which they resolve two superconducting gaps associated with the inner (IP) and outer (OP) CuO2 planes. CuC-1234 has a Tc as 117 K in a sample previously structurally characterized using neutron powder diffraction. From the Luttinger sum, the beta-band of the IP was found to be heavily underdoped (p~0.07) while the OP alpha2 bonding band was strongly overdoped (p~0.25). Each revealed a gap with very different momentum and temperature dependences. A large gap on the beta band was found to close at the bulk Tc, while a smaller gap on the alpha2 band closed at 70 K. Such two-gap behavior would indicate weak-coupling between the IP and OP, resulting in a second gap-opening temperature, Tc2, and implying a two-step development of the superfluid density on cooling, first on the IPs then on the OPs. Here, we point out that the observed values of Tc and Tc2 are fully consistent with a long-standing correlation of Tc with a bond-valence sum parameter, V+, calculated from the crystallographic bond lengths. This suggests that Tc2 in the OP is entirely consistent with the local structure of the OP where the value of V+(OP) is reduced by the presence of the apical oxygens and Tc2 reduced accordingly. It is as though two largely decoupled superconductors are present in the single 1234 compound and their individual pairing temperatures are determined by their local nearest-neighbour structure, reflecting the very short-range physics.

Bound states and resonances induced by short-range impurities modeled by circular potential wells are analyzed in the vicinity of flat and dispersive bands in gapped and gapless pseudospin-1 systems. We find that the bound and resonant states derived from the flat band show unusual characteristics originating from the multicomponent structure of pseudospin-1 fermions, which are distinct from those for pseudospin-$\tfrac{1}{2}$ fermions. Contrary to gapped Dirac systems and unlike bound states in the vicinity of the upper dispersive band, the bound states derived from the flat band occur for any value of the total angular momentum. The energies of these bound states with higher angular momentum $j$ tend to decrease with $|j|$. In addition, it is found that their wave functions are localized at the potential well edge and the localization increases with $|j|$. The signatures of the impurity states in the local density of states are determined. Using the Anderson model for independent electrons in the disorder potential, the thermodynamic potential, entropy density, and heat capacity are obtained. In the regime dominated by bound states derived from the flat band, the entropy density monotonically increases with temperature and saturates, whereas the heat capacity exhibits a single maximum.

Photonic bandgaps can open not only in crystalline dielectric materials but also in amorphous structures. Self-uniform amorphous gyroid networks have been proposed as promising disordered photonic architectures. Motivated by numerical studies, we combine direct laser-writing lithography with advanced materials processing to fabricate these structures from high-refractive-index silicon. Spectroscopic measurements at mid-infrared wavelengths reveal pronounced transmission minima. To investigate the formation of photonic band gaps in amorphous structures, we develop polarization-resolved transmission spectroscopy that separates ballistic and multiply scattered contributions, enabling direct identification of the underlying transport regimes. We observe a strong suppression of diffuse transmission, providing direct experimental evidence for a breakdown of conventional diffuse transport associated with a strongly reduced photonic density of states. Together with large-scale numerical simulations, our results establish the presence of a deep photonic pseudogap in an amorphous three-dimensional dielectric material and open new opportunities for observing disorder-induced localization phenomena, including Anderson localization of light.

Lattice-based metamaterials provide lightweight platforms where local instabilities can govern the global mechanical response, enabling applications in energy routing, vibration isolation, and impact mitigation. Although much progress has been made in controlling deformation and buckling sequences through geometric design, the behavior of coupled nonlinear units over a large range of strain rates and their history-dependent response is less explored. Here, we investigate lattice-based mechanical metamaterials whose nonlinear buckling behavior can be harnessed through modular architectures. By combining modular units in series, we show that their interaction gives rise to emergent force responses, including transient weakening and enhanced force attenuation, that are absent in the individual modules. Furthermore, selected designs exhibit training behavior under cyclic loading, transitioning between distinct buckling states and revealing a history-dependent mechanical response. Our results demonstrate that modular, instability-driven metamaterials can be programmed and tuned not only through geometry but also through loading history, opening new avenues for designing a nonlinear stress-response in mechanical systems.

Lattice vibrations carrying angular momentum give rise to fundamental phenomena such as the phonon Hall effect and the Einstein-de Haas effect, offering new opportunities for manipulating angular momentum in condensed-matter systems. Generating such circularly polarized phonons requires either the use of an external magnetic field, or of polarized light pulses. The latter approach does not require the use of any magnetic response of the material, but it has limitations, in particular regarding the duration of the pulse. Consequently, any effect stemming from phonons generated by light pulses is transient. In this paper, we propose the use of a driven electromagnetic cavity as a route to generate a steady-state population of chiral phonons. We derive a general description of cavity-chiral phonon interaction, with a particular focus on modes of chiral cavities. We show that, under optimized conditions, a significant effective phonon-induced magnetic field can be generated by means of an external drive with realistic power. Our approach is specially tailored for Gamma point phonons with THz frequencies, and opens a new route for investigating chiral phonons with electromagnetic cavities.

Hyperelastic constitutive models enable modeling large deformations in elastic solids. In common practice, a strain energy density function is prescribed in advance and model-specific parameters are calibrated from experiments. However, many applications require constitutive models for a family of related materials whose mechanical behavior varies with composition. A fixed constitutive model-form may not capture the full range of behavior across the family, while fitting separate forms does not provide a direct way to predict the response of new compositions. Recent work has developed data-driven constitutive models that learn flexible strain energy functions while incorporating key physical constraints. In this work, we propose using mixtures of convex neural potentials based on input convex neural networks as a modular and data efficient approach to modeling material families. Each potential is convex and monotonic with respect to polyconvex strain invariants, while a conditioning network maps material descriptors to mixture weights. We compare the approach with a monolithic partially input-convex neural network using experimental data from PolyJet 3D-printed materials and a synthetic Gent-type benchmark. Across both benchmarks, the mixture architecture generalized better to material descriptors not seen during training. In the PolyJet experimental benchmark, we showed that the mixture architecture is less sensitive to model hyperparameters, while in the Gent-type benchmark it generalized more reliably with sparse data in the material-descriptor space. These results suggest that representing a material family through a small set of shared convex neural potentials provides a useful structural prior for learning descriptor-dependent constitutive behavior from limited data.

Direct-space and real-time coherent X-ray imaging (direct-CXI) enables visualization of magnetic-domain structures and dynamics over length scales exceeding the field of view of a single image. However, large-area measurements typically require raster scanning, producing hundreds of partially overlapping images that must be accurately aligned and combined before quantitative analysis can be performed. Here, we present Multi-image Overlap Stitching and Automatic Image Construction for coherent X-ray imaging (MOSAICX), an automated stitching workflow for large-area direct-space coherent X-ray imaging. The workflow consists of image centering, masking, trimming, binarization, hierarchical stitching, and post-processing. To demonstrate the method, we apply it to a dataset comprising 434 direct-CXI images of the antiferromagnetic topological insulator MnBi$_2$Te$_4$. The images are first combined into column reconstructions and subsequently stitched into a single large-area composite image. The resulting reconstruction reveals the complete magnetic-domain and domain-wall landscape over the scanned region while suppressing imaging artifacts and detector defects. The presented workflow provides an efficient approach for processing large direct-CXI datasets and enables visualization and analysis of magnetic-domain structures beyond the field of view of individual measurements.

In flat band superconductors, quantum geometry, rather than kinetic energy, governs pairing and transport. However, how this geometry manifests in the response to a local, individually addressable impurity remains largely unexplored. Here, we study the Yu-Shiba-Rusinov (YSR) bound state induced by a magnetic adatom that hybridizes with every orbital of a two-dimensional flat band superconductor, and characterize its spatial profile using two quantities: the quadratic spread $Q_S$ and the localization length $\xi$. We show that $Q_S$ is not set by the quantum metric alone, as geometric corrections arising from inter-orbital interference and, more importantly, from the anisotropy of the adatom-lattice hybridization contribute on equal footing, making $Q_S$ strongly impurity dependent and tunable. On the other hand, $\xi$ emerges from the projection onto the flat band alone and is a universal property set by the overlap of compact localized states. All impurity dependence is instead isolated in the prefactor of the wavefunction whose magnitude correlates directly with $Q_S$. We, therefore, report a clean separation between universal and impurity-tunable physics from the induced YSR bound state in these systems, and confirm our results numerically via exact diagonalization.

Dynamical heterogeneities are one of the hallmarks of supercooled liquids, and their properties and relevance have been studied with theory, simulations and experiments. In this work, we propose to monitor the dynamics of tracer particles (passive microrheology) to analyze the dynamical heterogeneities in a system of hard colloids close to the glass transition density, using Langevin dynamics simulations and mode coupling theory. Different observables, typical in the study of the dynamical heterogeneities are adapted to be calculated from the trajectory of a single tracer particle. The tracer dynamics shows a transition from a regime where it is most decoupled from the bath for small tracer size to a strong coupling regime for large tracers. Both theory and simulations show that the non-Gaussian parameter of the tracer is maximal for tracer sizes at the crossover between both regimes, and is highly dependent on the bath density. The dynamic susceptibility is also studied, but this parameter shows a minor dependence on both the tracer size or the bath density. Finally, the existence of regions with different mobility is also studied with microrheology. Although the tracer trajectory indeed shows stages with increased mobility, the estimated size of the regions decreases with the bath density, contrary to the results from cluster analysis in the bulk.

Can an artificial intelligence (AI) generate a scientific hypothesis outside a human collaborator's active hypothesis space (AHS), and can human-AI research be organized to make such breakthroughs more likely? We document such a case while proving a theorem that connects two basic organizing mechanisms of statistical physics: collective behavior arising in zero field from competing interactions and that induced or controlled by an external field. A zero-field $O(n)$-vector open chain with arbitrary inhomogeneous nearest- and next-nearest-neighbor interaction functions $U_i(S_i\cdot{S}_{i+1})$ and $V_i(S_i\cdot{S}_{i+2})$ is microscopically, via a temperature-independent mapping at the Hamiltonian level, equivalent to a simpler $O(n)$ open chain with nearest-neighbor interaction $V_i(\boldsymbol\sigma_i\cdot\boldsymbol\sigma_{i+1})$ and axial single-spin potential $U_i(\sigma_i^z)$ for every integer $n\ge1$ and every system size $L\ge1$. The homogeneous linear specialization maps the foundational frustrated $J_1$-$J_2$ model onto the canonical $J$-$h$ field model—with $n=1,2,3$ being the Ising, XY, and Heisenberg classical spin models, respectively; the theorem resolved a longstanding challenge for $n=3$ published in 1990. Its proof was done with an AI-synthesized recursive Householder moving frame and understood via a human-recognized hidden reciprocity. An analogous theorem holds when the continuous $O(n)$ spins are replaced by the $q$-state Potts spins, implying a closed-form exact solution of the $J_1$-$J_2$ standard Potts open chain for every $q\ge2$ and every $L\ge1$. The emergence of these theorems from a human-AI co-development framework suggests that sustained AI involvement throughout a systematic research program may incubate autonomous scientific breakthroughs and make aspects of the discovery process experimentally testable.

Higher-gradient modifications of Newtonian gravity remove the point-mass singularity, but their Lagrangian dynamics is haunted by the Ostrogradsky instability. We show that the same field equations follow from the Second Law of thermodynamics applied to a self-gravitating fluid with a weakly nonlocal state space, and that on this route the instability is absent by construction: the potential obeys a first-order relaxation equation that is a gradient flow, whose Lyapunov function is the entropy density, and whose relaxation spectrum is negative definite at every wavenumber precisely when the entropy is concave. The derivation also yields the pressure tensor and the energy current, an exact identity that reproduces Newton's force law without further input, and a dissipation-free cross-coupling to the bulk viscous pressure that no variational principle can produce. Regularity constrains the Yukawa-type corrections by an amplitude sum rule, $\sum_i\alpha_i=-1$, so that laboratory tests of the inverse-square law bound the largest internal length below $4\times10^{-5}$~m, and identify the complex-root regime as a classically consistent Lee–Wick-like sector.

We propose a symmetry-guided route to engineer tunable $p$-wave magnetism in a bilayer system composed of two AB-stacked antiferromagnetic square lattices with their collinear moments nonparallel to each other. We show that an in-plane relative shift between the two layers selectively breaks the symmetries protecting spin degeneracy while preserving time-reversal-related constraints, thereby generating odd-parity spin splitting in a fully compensated magnetic state without spin-orbit coupling. The direction and the magnitude of the resulting $p$-wave spin-splitting, together with the associated spin responses, can be continuously tuned by the in-plane displacement, providing a potential knob for control. We further map the bilayer system onto an effective bond-modulated square lattice and investigate the corresponding Hubbard model within a mean-field framework. The calculated phase diagram reveals extended regions where $p$-wave magnetism with coplanar or chiral spin textures emerges spontaneously. Our results establish a minimal equilibrium platform for realizing and manipulating $p$-wave magnetism in two-dimensional systems.

Higher-order topological insulators are materials with a bulk energy gap featuring gapless modes at $(d-n)$-dimensional edges, where $n > 1$. Despite this modified bulk-boundary correspondence, their nontrivial topology can nevertheless be observed through the bipartite entanglement spectrum. Inspired by works suggesting fluctuations in conserved quantities could be used to study topology in one-dimensional systems, which likewise feature zero-dimensional edge modes, we extend this treatment to a two-dimensional second-order topological insulator where corner states play an analogous role. We show that the standard bipartite entanglement entropy and particle number fluctuation lack striking signals of topological phase transitions, both in the static case and in the time evolution after a quench, obscured by an area-law term from the subsystem edges. By introducing a quadripartite construction of the subsystem, we show that it is possible to isolate the topological contributions, producing sharp transition peaks in both quantities, observable by studying subsystems much smaller than the full system. As particle number fluctuations are accessible in existing experiments, these results establish a concrete and scalable path to experimental detection of the entanglement in higher-order topological insulators.

We report electron spin polarization of 95.0 +/- 0.8 (stat) +/- 2.4 (sys)% from a strained GaAs/GaAsP superlattice photocathode grown by metalorganic chemical vapor deposition (MOCVD) and cooled to dry-ice temperature (195 K). We achieved this polarization with 97.8% circularly polarized excitation light and a quantum efficiency of 0.7% at the peak polarization wavelength. This measurement exceeds the values of previously reported GaAs-based photocathode polarizations, which have clustered near 92% for two decades. We vary the temperature of the cathode and measure the polarization and quantum-efficiency spectra at 295 K, 273 K, 195 K, and 77 K. The polarization rises from 91.2(1)% at 295 K to its maximum at 195 K, while the spectral peak shifts from 775 nm to 739 nm (78 meV) over the full temperature range, tracking the widening band gap. The spectra probe two depolarization mechanisms: a thermalized transport channel that is suppressed on cooling, and energy-dependent hot-electron relaxation that persists and sets the low-temperature saturation. The polarization recovers after a full cooling and warmup cycle and is stable while the quantum efficiency decays, which disfavors surface energy filtering as the origin of the gain. These results indicate that modest cooling to 195 K, for which dry ice suffices, is a practical route to higher-polarization GaAs-based electron sources.

Truncated Coulomb (TC) potentials reduce finite-size errors and accelerate thermodynamic-limit convergence in periodic Hartree–Fock (HF) calculations, but their use with Gaussian basis sets is complicated by the evaluation of electron repulsion integrals (ERIs), particularly for nonspherical truncation domains and all-electron calculations. We introduce the smoothed truncated Coulomb (sTC) potential as a systematically improvable approximation to a parent TC potential. A real-space Gaussian convolution smooths the sharp truncation boundary, and a single dimensionless parameter, $\eta$, controls the width of the smoothing window, which can be tightened to systematically approach the TC reference. The smoothing by sTC enables a dual-space algorithm for evaluating periodic Gaussian-basis ERIs that requires neither a large plane-wave basis nor new molecular integral kernels and is applicable to both pseudopotential and all-electron calculations, including the important Wigner–Seitz-cell truncation boundaries. Benchmarks spanning insulating, semiconducting, layered, metallic, and molecular-crystal systems show that sTC-based HF closely reproduces TC results in pseudopotential calculations and extends TC-quality calculations to all-electron settings. Across these systems, sTC substantially improves thermodynamic-limit convergence relative to the probe-charge Ewald method while remaining practical for all-electron calculations in which direct TC-based calculations are computationally challenging.

We explore the hypothesis that ions form loosely connected clusters at high ionic strength in aqueous solutions, and that these clusters have relevance to the experimentally observed phenomenon usually referred to as "anomalous underscreening". Cluster formation lowers the ionic strength below its nominal value, slowing the decay of the screening length but not reversing it. Here we focus on an additional contribution, cluster polarisation. We demonstrate that this effect produces longer-ranged repulsive interactions between like-charged surfaces or particles in concentrated salt solutions. We derive an analytical bulk relation in which the entire architecture of a cluster enters through a single quantity, the charge-weighted second moment of its intramolecular charge structure factor, which quantifies the polarisation response of an arbitrary cluster topology. We also make numerical calculations using classical polymer Density Functional Theory, cDFT, for a model based on star-like clusters in which satellite ions are weakly bonded by a harmonic spring to a common central ion. The corona of satellite ions is assumed to be net neutral, since the formation of highly charged clusters would be accompanied by a significant self-energy cost. Using this model, we calculate surface interactions and screening lengths at various overall salt concentrations. We show that, under the assumption that the fraction of ions belonging to clusters increases with salt concentration, one may qualitatively arrive at "anomalous underscreening", i.e., an effective screening length that displays a minimum at an overall (monovalent) salt concentration of about 1 M. Quantitatively, we note that the predicted growth of the screening length beyond this threshold value is weaker than typically found by experimental surface force measurements.

We explicitly compute and tabulate the suspension map for cohomology operations, applying it to the dimensional reduction of anomalies and higher group structures of generalised symmetries in quantum field theories and lattice systems. In a quantum system with a discrete $p$-form symmetry, we can restrict the symmetry defects to a codimension-$q$ subspace of spacetime, or equivalently confine the gauge field to a slab whose thickness approaches zero. This results in a $(p-q)$-form symmetry on the subspace. We determine the fate of two important properties of symmetries under this process. First, we compute the anomaly of the reduced symmetry, or the higher anomaly of the original symmetry, which acts as an obstruction to higher gauging and onsiteability. Second, for two symmetries forming a higher-group structure, encoded as a Postnikov class, we compute the reduced higher-group structure, which may or may not be trivial. Both cases are captured by the $q$-fold iteration of the cohomology suspension $\Omega$, also known as the loop functor or transgression, in the cohomology of Eilenberg–MacLane spaces. Classical results state that $\Omega$ is an isomorphism in a stable range and annihilates mixed anomalies. To calculate $\Omega$ over a base ring which is not a field, we make use of small models for the chain DGAs of Eilenberg–MacLane spaces, pioneered by Cartan and Moore, whose results we review and extend. The critical added step is the improvement of a mod $p$ chain contraction to the $p$-local integers, obtained via a $p$-adic series. We automate the computations in a software package emcm, and provide extensive tables of the results. Finally, to make contact with explicit cochain formulations of cohomology operations, we demonstrate how to calculate cup products and certain cup-$i$ products in this framework.

Determining exact joint eigenvalue densities is central to random matrix theory. We solve this long-standing problem for non-Hermitian matrices with transposition symmetry (complex symmetric and complex self-dual) at arbitrary matrix size. Up to a Vandermonde factor, they are scattering-state wave functions of the Calogero model, a line of particles interacting through an inverse-square potential, with the coupling strength set by the symmetry. In contrast to many previously known joint densities, the densities cannot be written as a gas of eigenvalues with pairwise interactions. We further compute the complex level spacing distributions and two-point spectral correlation functions, which carry power-law tails, absent in a Coulomb gas. Our results shed light on the interplay among random matrices, integrability, and symmetry.

The complex spectral statistics of non-Hermitian random matrices provide a standard diagnostic of dissipative quantum chaos. Yet an analytical understanding of how symmetry enriches these universal correlations remains limited. We establish an exact duality between the spectral statistics of Hermitian and non-Hermitian random matrices in the limit of large matrix size. This duality resolves a longstanding analytical problem by yielding the previously unknown eigenvalue pair-correlation functions for complex symmetric (class AI$^\dagger$) and complex self-dual matrices (class AII$^\dagger$), completing the analytical description of bulk pair correlations in the non-Hermitian threefold way. It further gives closed-form spectral densities near the origin for seven additional symmetry classes. Numerical tests in interacting and dissipative quantum models support the universality of these predictions beyond Gaussian ensembles. The duality suggests a deeper connection between chaos in closed and open quantum systems.

We study thermal order in conformal field theories (CFTs) in $d=4-\epsilon$ and $d=3$ dimensions where several scalars are coupled to an $O(N)$ vector field. In $(4-\epsilon)$ dimensions, we consider models coupling a cubic model of $M$ scalars with $\mathbb{Z}_2^M\rtimes S_M$ symmetry (corresponding to sign flips and permutations of the scalars) to an $O(N)$ vector model. For any $M$, we find a window of $N$ in which two Wilson-Fisher-like fixed points exist. We show that the $\mathbb{Z}_2^M\rtimes S_M$ symmetry is spontaneously broken at arbitrary nonzero temperatures for $M=2$ and sufficiently large $N$ within this window, but it remains unbroken for $M>2$. Using the functional renormalisation group to continue these fixed points towards three dimensions, we find that they collide and move into the complex plane well before reaching $d=3$, suggesting that their continuation to $d=3$ does not yield unitary CFTs. We then work directly in three dimensions at large but finite $N$, with $M\ll N$, initially without assuming any permutation symmetry among the $M$ scalars. By studying the RG flow, we show that these models possess a conformal manifold up to the leading nontrivial order in the $1/N$ expansion of the beta functions (which is $\mathcal{O}(1/N)$). At each point on this manifold, the scalars split into two classes that are distinguished by how they couple to the $O(N)$ vector field. We then restrict to a subspace of the conformal manifold where there is an additional symmetry under permutations of the scalars within each class. We prove that in a domain of this subspace, all $M$ scalars acquire thermal expectation values such that the symmetry under sign flips of the scalars is spontaneously broken at all nonzero temperatures. This provides a novel class of large $N$ CFTs that exhibit a rich pattern of persistent symmetry breaking at nonzero temperatures.

A universal characterization of non-equilibrium steady states in interacting quantum many-body systems remains one of the central challenges of statistical physics. Here, we address this problem for a paradigmatic model of diffusive interacting quantum matter—the boundary-driven XXZ spin chain with bulk dephasing—and derive, directly from its microscopic Lindblad dynamics, an emergent classical Macroscopic Fluctuation Theory (MFT) governing its large-scale fluctuations. Crucially, the resulting hydrodynamics carries a density-dependent diffusivity and mobility as the fingerprint of interactions. This effective description enables the exact computation of the stationary density profile, long-range correlations, and the full counting statistics of the current, in excellent agreement with tensor-network simulations. Our work demonstrates that noisy quantum many-body systems can realize the universality class of genuinely interacting diffusive matter, beyond the constant-diffusivity class of the symmetric simple exclusion process, and establishes MFT as a powerful universal framework for interacting diffusive quantum systems.