Understanding the crystallization pathways of water-rich ammonia-water ($\mathrm{N}{\mathrm{H}}_3\text{−}{\mathrm{H}}_2\mathrm{O}$) solutions and the stability of ammonia hydrates is key to unraveling the behavior of complex hydrogen-bonding networks and to modeling planetary interiors. Yet there are still inconsistencies in the crystallization sequence reported upon pressure-induced crystallization of ${\mathrm{H}}_2\mathrm{O}$-rich $\mathrm{N}{\mathrm{H}}_3\text{−}{\mathrm{H}}_2\mathrm{O}$ solutions at room temperature. Here, we investigate the effect of compression rates on the crystallization pathways of 25 wt% $\mathrm{N}{\mathrm{H}}_3$ aqueous solutions at room temperature using dynamically compressed diamond anvil cells (dDAC) coupled with time-resolved x-ray diffraction. We show that compression rates exceeding 0.5 GPa/sec promote direct crystallization of a body-centered cubic (bcc) phase (DMA’) with possible AMH stoichiometry coexisting with ice VII, while rates below 0.2 GPa/sec stabilize monoclinic $\mathrm{N}{\mathrm{H}}_3$-rich AHH-II and ice VII phases. Intermediate rates between 0.2 and 0.5 GPa/sec produce a mixture of both hydrates alongside ice VII, hence demonstrating the role of compression rate on the crystallization sequence of ammonia solutions. The compression behavior and phase stability of the distinct phase assemblies (AHH-II/DMA’ + ice VII) are investigated further to place constraints on the composition of the DMA’ phase, the effect of ice VII on the compressibility of ammonia hydrates, and the plausible incorporation of $\mathrm{N}{\mathrm{H}}_3$ impurities within the lattice of high-pressure ice phases.

Cold atom arrays in optical lattices offer a highly tunable platform for exploring complex quantum phenomena that are difficult to realize in conventional materials. Here, we investigate the emergence of controllable long-range quantum correlations in a simulated twisted bilayer structure with fermionic cold atoms. By exploiting the incommensurate nature of the twisted bilayer, we observe a significant enhancement of long-range susceptibility, suggesting the formation of stable entangled states between spatially distant localized spins. We further show that the tunability of the interlayer coupling in terms of driving fields enables us to manipulate these entangled states without deformation of lattice structure and extra doping. Our findings provide a pathway for overcoming challenges in establishing strong correlations across distant sites, highlighting the potential of optical lattices as a versatile platform for advanced quantum technologies.

The isotope effect in superconductors can be influenced by electronic structure features such as flat bands and Van Hove singularities, providing a pathway for tuning superconducting properties. Using first-principles calculations within the framework of conventional electron-phonon coupling in the harmonic approximation, we predict superconductivity in the oxygen superhydrides ${\mathrm{H}}_3\mathrm{O}, {\mathrm{D}}_3\mathrm{O}$, and ${\mathrm{T}}_3\mathrm{O}$ for Coulomb pseudopotential ${\mu }^{*}$ values ranging from 0.1 to 0.13. Notably, the compressed ${\mathrm{H}}_3\mathrm{O}$ exhibits an extraordinary near-room-temperature superconducting transition at 301.5 K, while the corresponding ${\mathrm{D}}_3\mathrm{O}$ and ${\mathrm{T}}_3\mathrm{O}$ show superconducting transitions at 247 and 218.8 K, respectively, in accordance with the expected isotope effect. To characterize the flat band near the Fermi level, which is closely related to the superconductivity in these systems, we define the flat-band depth $d$ as its energy distance below the Fermi level. Our calculations reveal a systematic decrease in $d$ with increasing hydrogen isotope mass, while the height $h$ of the Van Hove singularity at the Fermi surface increases with increasing isotope mass. We uncover a striking linear relationship between the superconducting critical temperature and the product of $d$ and $h$ and further demonstrate the universal existence of this linear relationship across the chalcogen superhydrides. By separating the pure phonon-mass effect from the isotope-induced electronic-structure evolution, we show that the latter provides a significant contribution to $T_c$, quantitatively captured by the product $d\times h$. These findings provide interesting insights into the interplay between flat-band physics and the isotope effect in superconductors, offering instruction for the design of novel high-temperature superconductors.

We investigate the zero-temperature transition from the polarized normal phase to the FFLO state in a two-dimensional Fermi gas by means of a diagrammatic $t$-matrix approach. We first show that the standard non-self-consistent theory produces an unphysical critical polarization because of a severe violation of the Luttinger theorem. Motivated by this observation, we introduce a minimal self-consistent extension that largely restores compliance with the Luttinger theorem while preserving the analytical simplicity of the original formalism. This leads to a physically consistent critical polarization over the whole interaction range. Building on this improved description, we characterize the quantum critical behavior of the FFLO transition through the quasiparticle decay rates, quasiparticle weights, momentum distributions, and the critical dynamics of both fermionic and bosonic degrees of freedom. We further compare the two- and three-dimensional systems, showing that their critical properties can be understood within a unified geometrical picture based on the nesting of the majority and minority Fermi surfaces. Finally, for a three-dimensional lattice, we demonstrate within the Hertz–Millis framework that vertex corrections are irrelevant, thereby placing the FFLO quantum phase transition in the mean-field universality class, in close analogy with the itinerant antiferromagnet transition.

One of the central goals in the emergent field of altermagnetism is the unambiguous experimental identification and characterization of altermagnetic order across a variety of compounds. This motivates exploring tools that can clearly distinguish altermagnets from antiferromagnets, based on symmetry signatures, and offer access to the dominant orbital character (e.g., $d$-wave versus $g$-wave) of the magnetic order parameter. In this work, we theoretically explore the potential of noise magnetometry for this task, studying contributions from both magnons and itinerant electrons in different regimes and scenarios. While altermagnetism and antiferromagnetism also lead to different noise spectra for magnons, we find the most striking and symmetry-sensitive signatures in the charge fluctuations of itinerant altermagnets. Both for the homogeneous bulk case and in the presence of strain and/or around domain walls, we identify noise contributions that are only permitted by symmetry in the altermagnet and, thus, provide a unique signature of altermagnetism. Furthermore, the angular dependence of noise around domain walls also offers access to the orbital character of the altermagnet. On a more technical note, we discuss the role and relevance of lattice effects related to the dipole tensor. We hope that our work will help pave the way toward the clear experimental identification of altermagnetism across a wide range of candidate materials.

The electromechanical responses in ferroelectric oxides are governed by the interactions between point defects and local polarization structures, where defect-induced internal fields can strongly modify domain switching behavior. While the effects of defect type and concentration on macroscopic properties have been widely explored, the role of defect spatial correlation in mediating local structural heterogeneity and collective polarization switching remains poorly understood. Here, combined electrical transport, local-structure, and atomic-scale polarization analyses reveal a reversible transition between correlated and dispersed defect states in ${\mathrm{BiFeO}}_3\text{–}{\mathrm{BaTiO}}_3$ ceramics. Quenching above the Curie temperature freezes a dispersed defect configuration, whereas slow cooling or annealing restores correlated defect-dipole states. The correlated state generates strong internal fields, fragmenting polar domains and suppressing cooperative switching, while the dispersed state weakens defect pinning, promotes a continuous polar network, and enables enhanced electromechanical response. These results show that defect spatial correlation can serve as a thermally programmable structural parameter for ferroelectric domain engineering, providing a strategy for the design of high-performance ferroelectric materials.

The anomalous Hall conductivity of a ferromagnetic two-dimensional electron gas with a Rashba spin-orbit interaction is studied in the presence of Gaussian white noise. In this condition the anomalous Hall conductivity can be separated into two parts, intrinsic and side jump. The intrinsic contribution first proposed by Karplus and Luttinger is mostly considered to be scattering independent and only depends on the band structure. Our results show that the anomalous Hall conductivity is sensitive to the disorder strength. Through an analysis of the spectral functions and cross terms of the Green's functions, we reveal that disorder-induced band broadening promotes interband spectral overlap, thereby suppressing the anomalous Hall conductivity. Furthermore, we find that in the regime where both subbands are occupied, the anomalous Hall conductivity is vanishing, due to a cancellation between the Fermi-surface contribution in the intrinsic part and the side-jump part.

Spin-dependent reflection of very low energy electrons from the surfaces of antiferromagnetic NiO and altermagnetic MnTe is studied within a Bloch-waves scattering theory. Significant spin polarization is observed both at normal and at off-normal incidence comparable to that in reflection from ferromagnetic Fe(100). This establishes electron diffraction as a useful tool to study compensated magnets and widens the range of materials promising as spin detectors. The spin filtering effect is shown to be due to the multiple scattering in the bulk of the crystal as it decreases with increasing the surface sensitivity of scattering. Opposite time-reversal parity of the bulk signal from antiferro- and altermagnets is revealed. However, the reflection spin asymmetry does not necessarily imply spin splitting and cannot be used to distinguish between antiferro- and altermagnets.

We have performed a detailed temperature-dependent study of optical f-f transitions of the $\mathrm{Y}{\mathrm{b}}^{3+}$ ions in $h-{\mathrm{YbMnO}}_3$ by means of Fourier-transform spectroscopy. The splitting of the ground Kramers doublet as a function of temperature, ${\mathrm{\Delta }}_0\left(T\right)$, was determined for the $\mathrm{Y}{\mathrm{b}}^{3+}$ ion at the $4b$ site. The ${\mathrm{\Delta }}_0\left(T\right)$ function follows the dynamics of the manganese magnetic moment below $T_N=87$ K, indicating that the ytterbium subsystem is magnetized by the magnetic field generated by an ordered manganese subsystem, which is consistent with the results of previous studies. Excitation of the upper component of the split ground doublet plays a significant role in the low-temperature dynamics of the $h\text{−}{\mathrm{YbMnO}}_3$ crystal. Using the ${\mathrm{\Delta }}_0\left(T\right)$ function, we calculated the temperature behavior of the $\mathrm{Yb}(4b$) magnetic moment: it is in clear agreement with the neutron data [S. Chattopadhyay et al., Phys. Rev. B 98, 134413 (2018)]. The calculated contribution of $\mathrm{Yb}(4b$) to heat capacity definitely explains the origin of the Schottky anomaly in the $C$($T$) dependence. A scenario for phase transitions in $h\text{−}{\mathrm{YbMnO}}_3$ is proposed, in which the energy gain in the ytterbium system plays a key role. A phase transition at 3.5 K is interpreted as spin reorientation.

We investigate heat conduction and energy relaxation in an InAs semiconductor nanowire using a hybrid semiconductor-superconductor architecture. Local electronic temperatures are measured with an $\mathit{in}$situ grown quantum dot thermometer, while controlled Joule heating is applied at different locations along the wire to probe the heat flow along the nanowire at subkelvin temperatures. With a one-dimensional heat transport model, we calculate an electron-phonon heat flow that scales as $Q_{\text{e-ph}}\propto T^{2.6}$, which is in close agreement with the $T^3$ dependence predicted for clean one-dimensional phonons coupled to the electron gas. We further estimate a characteristic length $l_{\mathrm{eq}}=370\mathrm{nm}$; beyond this length scale, phonon-mediated heat transport dominates over heat conduction in our nanowire. Our results provide a quantitative measure of energy relaxation mechanisms in a one-dimensional semiconductor and provide a framework for studying heat flow in low-dimensional nanostructures.

Ruddlesden-Popper (RP) nickelates have attracted intense interest following the discovery of superconductivity in several members of the series, including bilayer (BL) ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$, trilayer (TL) ${\mathrm{La}}_4{\mathrm{Ni}}_3{\mathrm{O}}_{10}$, and structural polymorphs composed of monolayer-bilayer or monolayer-trilayer (ML-TL) units. However, an inherent propensity of the RP series to form intergrown phases during single-crystal synthesis, together with spatial variations in oxygen stoichiometry, has complicated the determination of their intrinsic material properties. As a consequence, conflicting reports have emerged on both their electronic phase transitions and lattice dynamics. In this work, we perform a comparative study of the phononic and electronic Raman responses of high-quality ML-TL single crystals and contrast them with those of the other RP nickelates, using samples with optimized oxygen content. We establish several Raman spectral features that enable unambiguous phase identification across the series. Moreover, we uncover characteristics in the phononic and electronic Raman response of ML-TL that are not reflected in the pure ML and TL compounds. We attribute these differences to a distinctive electronic structure arising from self-doping and confinement effects induced by the ML unit within the ML-TL lattice architecture.

Off-stoichiometry Heusler-like compounds provide a platform in which fractional site occupation can generate local orbital inequivalence beyond the conventional Slater-Pauling electron-counting picture. Here, we investigate the $\mathrm{XC}{\mathrm{o}}_{1.33}\mathrm{Z}$ family using first-principles density functional theory and dynamical mean-field theory (DMFT), and show that mixed 4c/4d occupation creates inequivalent Co-$e$ states with distinct orbital fillings, hybridization strengths, and correlation responses. The resulting 4c/4d inequivalence drives a short-range interplay between Co-$e$ states, establishing a local orbital configuration that underlies magnetic compensation. Crucially, our DMFT calculations reveal that this compensated state is not a simple uniform band-semiconducting ferrimagnet, but an orbital-differentiated correlated state characterized by a site-selective low-energy resonance on the ${\mathrm{Co}}^{4\mathrm{d}}\text{−}e$ orbital and a pseudogaplike spectral suppression on the ${\mathrm{Co}}^{4\mathrm{c}}\text{−}e$ orbital. High-throughput calculations across 27 $\mathrm{XC}{\mathrm{o}}_{1.33}\mathrm{Z}$ compositions further show that X-Z sublattice tunes the Co-$e$-orbital interplay, producing strong, moderate, and weak interplay regimes. The moderate-interplay regime provides the key window for compensated ferrimagnetism and potential orbital-differentiated correlated state. These results identify off-stoichiometry Heusler-like compounds as a tunable platform for realizing correlated electronic states coupled to macroscopic magnetic compensation.

Moiré ferroelectric systems exhibit stacking-dependent interfacial polarization at the atomic thickness limit, inspiring a promising platform for next-generation devices. This unique ferroelectricity has been explored using a range of techniques. However, the built-in electric field arising from piezoelectric force microscopy (PFM) tip-sample contact often leads to amplitude imbalance and reduced phase contrast, complicating reliable characterization. Here, using twisted hexagonal boron nitride as a model system, we develop a multimodal scanning probe microscopy (SPM) strategy that combines noncontact Kelvin probe force microscopy (KPFM) with contact-mode PFM. By introducing a DC bias during PFM, we effectively compensate the built-in field. This compensation restores intrinsic moiré ferroelectric states, evidenced by straighter domain walls and a nearly 180° phase difference between adjacent domains. Our findings highlight the critical role of work function evaluation in PFM measurements and provide a reliable approach for probing moiré ferroelectric domains and their polarizations.

We numerically investigate excitonic complexes in semiconducting single-walled carbon nanotubes (sSWCNTs) using the diffusion Monte Carlo method. These complexes include the neutral polyexcitons (${\mathrm{X}}_n$), consisting of $n$ excitons, and charged polyexcitons (${\mathrm{X}}_n^{-}$), containing an additional electron. To this end, we develop an effective one-dimensional (1D) model that incorporates form factors, screened carrier interactions, and the spin and valley internal degrees of freedom of electrons and holes. We find that neutral polyexcitons are stable up to $n=4$, while charged polyexcitons remain stable up to $n=3$, independent of interaction strength. The energy needed to remove an exciton from ${\mathrm{X}}_n^{-}$ is larger than that from ${\mathrm{X}}_{n+1}$. This unusual result arises from the screening of the short-range part of the electron-hole attraction and the antiscreening of the long-range part of the electron-electron (or hole-hole) repulsion. Analysis of multiparticle correlation functions reveals that these complexes resemble an electron-hole droplet rather than a rigid excitonic molecule, although electrons still act as a glue binding neighboring hole pairs. The separation energies of sSWCNTs exhibit a convex upward $n$-dependence, in sharp contrast to the linear-in-$n$ increase found in 2D multivalley semiconductors, which originates from the 1D geometry of the system that limits the formation of equivalent covalent bonds among all hole pairs.

Quantum Monte Carlo simulations confirm the existence of a bound state of a single ${}^3\mathrm{He}$ atom at a free superfluid ${}^4\mathrm{He}$ surface in three dimensions, localized within an $\sim 10$-Å-thick low-density ${}^4\mathrm{He}$ surface layer, with a binding energy of approximately 5 K with respect to vacuum. As the temperature is raised above $\sim 1$ K the ${}^3\mathrm{He}$ atom leaves the surface to dissolve into the superfluid. The situation is entirely different in two dimensions, as the ${}^3\mathrm{He}$ atom is excluded from the superfluid and no surface bound state exists. Results are also presented for a ${}^3\mathrm{He}$ atom binding to nanoscale size ${}^4\mathrm{He}$ clusters adsorbed on weak substrates, a physical system that may allow for the observation of some of the physics predicted for extended surfaces. It is shown that a ${}^3\mathrm{He}$ bound state localized at the perimeter of sufficiently small (a few tens of atoms) clusters exists not just on Cs, as previously reported, but on all alkali substrates.

Reservoir engineering can stabilize states inaccessible to unitary dynamics. Directed particle-conserving dissipation creates Lindbladian skin states, where Pauli exclusion turns edge accumulation into a many-body density imbalance. In a monitored fermion chain with tunable hopping range, we identify, within a Gaussian trajectory approximation, two finite-size scaling regimes: Short-range hopping is consistent with complete skin accumulation and area-law entanglement, whereas sufficiently long-range hopping produces a finite bulk tail and effective algebraic sub-volume-law entanglement. Dissipation and coherent hopping thus jointly control skin localization and quantum entanglement, highlighting their close interconnection.

Quantum oscillations, terahertz cyclotron resonance and two-carrier Hall analysis of polarization-induced GaN/AlN two-dimensional hole gases report subband masses and lifetimes that disagree. We solve the six-band $k·p$ problem self-consistently with Poisson's equation at the measured density, with a finite AlN barrier. The computed heavy-hole mass, 1.92 to $1.99m_0$, agrees with the measured $1.92\pm 0.16m_0$; the cyclotron-resonance value differs because that resonance is overdamped. The two measured subband densities share one Fermi level only if the light-hole band is about one and a half times heavier than calculated, the discrepancy that both techniques report in the light-hole mass. Only $A_6$, the least well determined band parameter, moves the light subband alone. Rescaled to the measured light-hole density, it leaves the heavy holes unchanged, agrees with the light-hole cyclotron-resonance mass of a second sample and gives a Lifshitz-Kosevich mass that rises with field; as it lies near the limit of a bounded Hamiltonian, we treat it as an effective parameter. For scattering, a coupled two-subband Boltzmann equation excludes any single mechanism. The heavy-hole quantum mobility, inferred from the onset of its oscillations, is overestimated, because the heavy holes dominate the resistance; a Dingle fit of the published oscillations and their amplitude ratio both give 95 instead of 167 to $200{\mathrm{cm}}^2\mathrm{V}{}^{-1}{\mathrm{s}}^{-1}$. The four mobilities then fix the long-range disorder spectrum, $q^{-3.2}$ to $q^{-3.6}$, between in-plane and threading charged lines, and the two-carrier Hall analysis is not the cause of the disagreement.

The interlayer electronic coupling in twisted bilayer graphene results in band anticrossing of the intersected Dirac cones. The shifts of the two new band extrema relative to the original intersection point are crucial for the electronic and optical properties. However, such shifts, particularly, the possible asymmetric band repulsion in the band anticrossing, are still elusive. Here, using infrared spectroscopy, we reveal the asymmetric band repulsion for twisted bilayer graphene under ambient pressure and with pressure up to 4 GPa. The optical resonance peak undergoes redshift under pressure, in stark contrast to natural bilayer and multilayer graphene. In conjunction with tight-binding calculation, we also reveal that twisted bilayer graphene exhibits a notably smaller out-of-plane elastic constant than that of the natural bilayer. Our study paves the way for mechanical tuning of the transport and optoelectronic properties of twisted bilayer graphene, in particular, achieving flat bands in broader twist angles.

Boron's electron deficiency favors multicenter bonding and enables planar or quasiplanar boron nanostructures with unusually stable pristine edges and corners. Yet a compact bonding picture that explains these stability trends remains elusive. Here we introduce a bonding model for triangular-lattice-based planar boron clusters, defined by four bonding rules that use only 3c-2e and 2c-2e bonding and σ bond resonance. The model allows intuitive construction of σ bonding configurations without extensive quantum calculations, revealing the origin of the high stability of planar boron clusters and rationalizing their effective self-termination at pristine edges and specific corners. From this model we extract three stability criteria: energetically favored clusters tend to have (i) obtuse-angle convex and/or concave corners, (ii) flat edges with an even number of atoms, and (iii) an increasing number of hexagonal holes as the cluster grows. Applying these criteria, we predict ${\mathrm{B}}_{49}, {\mathrm{B}}_{70}$, and ${\mathrm{B}}_{84}$ as particularly stable planar clusters beyond the well-known ${\mathrm{B}}_{36}$, reproducing density-functional theory trends in formation energies. Independent validation using a machine learning force field–accelerated global structure search across both planar and three-dimensional manifolds confirms these predictions, while energy gaps, in this size range, remain small enough that planar forms stay competitive and are further stabilized on substrates. This resulting framework provides fundamental insights into boron chemistry and a practical route to rational design and scalable prediction of boron-based nanostructures.