Helium and methane are the important constituents of ice giants in the solar system. As such, the behavior of methane-helium mixtures at high pressure offers insights into the structure and composition of interiors of ice giants. Here, we report on the room-temperature high-pressure phase diagram of methane-helium mixtures with helium concentrations from 10% to 98% examined by Raman spectroscopy and visual observation. Several two-phase equilibria and a liquid-liquid-solid three-phase equilibrium are observed upon loading and unloading pressure. Furthermore, based on the Raman vibrational frequency and corresponding full width at half maximum (FWHM) of C-H stretching vibration mode $v_1$, we estimated helium concentrations of methane-rich fluid $\left({\mathrm{F}}_1\right)$ and helium-rich fluid $\left({\mathrm{F}}_2\right)$ in different methane-helium mixtures. In addition, Raman measurements for solid phase $\left({\mathrm{S}}_1\right)$ across all mixtures suggest helium can hardly dissolve in ${\mathrm{S}}_1$ at high pressure.

We investigate quantum inverse problems in one-dimensional (1D) electronic disordered systems strongly coupled to optical cavities. More specifically, we consider the Anderson and the Aubry–André–Harper models connected to electronic reservoirs and embedded in a single-mode optical cavity. The light–matter interaction enables photon-assisted hopping processes that significantly modify the transmittance spectrum. Within the nonequilibrium Green's function formalism, we implement an inversion-based approach capable of accurately extracting the electron–photon coupling strength directly from transmittance spectra. While cavity coupling acts as a minor perturbation within the Anderson model, yielding broad yet precise parameter estimates, its influence is markedly different in the Aubry–André–Harper model. The latter exhibits a sharp metal–insulator transition in 1D, thus resulting in more pronounced cavity-induced spectral changes. This renders even more accurate inverse solutions, offering unparalleled precision in the characterization of low-dimensional disordered systems. Altogether, our results demonstrate that the quantum inverse problem provides a robust diagnostic tool for quantum materials, particularly effective for systems exhibiting metal–insulator transitions.

In this work, we report on the thermomagnetic characterization and crystalline-electric field (CEF) energy scheme of the disordered defect-fluorite ${\mathrm{Ho}}_2{\mathrm{Zr}}_2{\mathrm{O}}_7$. This structural phase is distinguished by the coexistence of magnetic frustration and extensive disorder, with ${\mathrm{Ho}}^{3+}$ and ${\mathrm{Zr}}^{4+}$ sharing randomly the same $4a$ site with even 50% occupancy, and an average 1/8 oxygen vacancy per unit cell. AC magnetic susceptibility measurements performed on powder samples down to 0.5 K revealed signs of slowing spin dynamics without glassy behavior, including a frequency dependent peak at $\sim 1\mathrm{K}$. Yet, no evidence for long-range magnetic order is found down to 200 mK in the specific heat. Inelastic neutron scattering measurements show a weak, low-lying CEF excitation around 2 meV, accompanied by a broad level centered at 60 meV. To fit our observations, we propose an approach to account for structural disorder in the crystal-field splitting of the non-Kramers ${\mathrm{Ho}}^{3+}$. Our model provides an explanation to the broadening of the high-energy, single-ion excitations and suggests that the zirconate ground-state wavefunction has zero magnetic moment. Through the breaking of local symmetry, structural disorder enables the magnetic response observed in ${\mathrm{Ho}}_2{\mathrm{Zr}}_2{\mathrm{O}}_7$, allowing the mixing of low-lying states at finite temperatures. Finally, we show that this scenario is in good agreement with the bulk properties reported in this work.

Many-body interactions strongly influence the structure, stability, and dynamics of condensed-matter systems, from atomic lattices to interacting quasiparticles such as superconducting vortices. Here, we theoretically investigate pairwise and many-body interaction terms among skyrmions in helimagnets, considering both the saturated ferromagnetic and conical spin backgrounds. Using micromagnetic simulations, we calculate the exchange, Dzyaloshinskii-Moriya, and Zeeman contributions to the skyrmion-skyrmion pair potential, thereby identifying the physical origin of the attractive and repulsive regimes. For small skyrmion clusters in the conical phase, three-body interactions provide a substantial contribution to the cohesive energy, comparable in magnitude to the pairwise term, whereas four-body contributions become relevant only at low magnetic fields. As the system approaches the saturated phase, higher-order terms vanish and the interaction becomes essentially pairwise. These results demonstrate that realistic descriptions of skyrmion interactions in helimagnets, especially in the conical phase, require explicit many-body terms in order to capture the behavior of skyrmion crystals and to guide strategies for controlling skyrmion phases and dynamics.

Generating and characterizing uniform and staggered spin polarization in antiferromagnets is one of the key challenges for antiferromagnetic (AFM) spintronic technology. Here, we perform perturbative theory, group-theoretical symmetry analysis, and low-energy and ab initio simulations to propose that the magnetic precession near the equilibrium magnetic axis could generate finite uniform and staggered spin polarizations at the opposite magnetic sublattices (referring to total magnetic and Néel vector generation) in a single AFM semiconductor. This response does not require the heterojunction setup and could eliminate the lattice mismatch issues at the junction. Through scrutinizing all magnetic groups with symmetrically protected vanishing magnetic moments, and especially focusing on parity-time $\left(\mathcal{PT}\right)$ invariant groups, we identify the symmetry constraints that describe the staggered spin accumulation responses, and disclose their fieldlike and dampinglike characters. This unravels a hidden spin accumulation mode in AFM semiconductors. Furthermore, we simulate such an effect using a perturbative approach and suggest that an electric gate field and Floquet light dressing can effectively manipulate these responses.

Kagome materials are known for hosting emergent quantum phenomena driven by the interaction between different lattice, charge, and spin orders. Here, we present a detailed angle-resolved photoemission (ARPES), density functional theory (DFT), and x-ray magnetic circular dichroism (XMCD) study of the electronic and magnetic structure of $R{\mathrm{Ti}}_3{\mathrm{Bi}}_4$ $(R=\mathrm{Nd}, \mathrm{Sm}, \mathrm{Gd})$. ARPES and DFT demonstrate that the bulk electronic band structure is dominated by the hybridization of the Ti bands, and the weak electron-like pocket at $\mathrm{\Gamma }$ is identified as a surface state. The isotropic XAS profile of the $M_{4,5}$ edge of the rare earth is consistent with the presence of the $R^{3+}$ oxidation state. Using the XMCD sum rules, backed by the atomic-multiplet-theory calculations, we obtain the spin and orbital magnetic moments. The Ti $L_{2,3}$-edge XMCD reveals the presence of a small magnetic moment in ${\mathrm{GdTi}}_3{\mathrm{Bi}}_4$, presumably driven by the proximity of the Ti kagome layers to the zigzag chains of Gd, while the total magnetic moment of Gd is shared by the $f$ and $d$ electrons. Our combined XMCD, ARPES, and DFT study provides an important piece of information to understand the spin-flip transitions and anomalous Hall effect observed in the $R{\mathrm{Ti}}_3{\mathrm{Bi}}_4$ kagome metals.

We use time-resolved thermometry to monitor the decay of nonequilibrium quasiparticles in superconducting Al in the temperature range from $0.3$ to $1.2\mathrm{K}$. The quasiparticle lifetime at higher temperatures ($T>0.7\mathrm{K}$) agrees well with the calculated energy flow from electrons to phonons, but at lower temperatures it is significantly shorter than the theory predicts. We show well-defined internal equilibrium of quasiparticle system in the studied thermal transients, which implicates that quasiparticle-quasiparticle relaxation is much faster than electron-phonon interaction.

In this work we extend our study of the effect of certain crystallographic defects on the spin-1/2 Kitaev honeycomb spin liquid, focusing on its gapless phase and contrasting with the gapped phase. We identify a Stone-Wales (SW) local defect consisting of a ${90}^{\circ }$ bond rotation that preserves Kitaev bond labels for edge-sharing octahedra and thereby enables exact solvability. These SW-type defects involve odd-sided plaquettes with $\pm \pi /2$ fluxes, but can be created locally. An isolated defect hosts a time-reversal pair of ground-state flux configurations with large net chirality. Certain excitations are also chiral. The chirality manifests in Majorana local Chern marker and in scalar spin chirality, producing electronic orbital magnetization. T-matrix analysis and numerics at finite defect density $n_d$ show that defect chiralities generate a topological gap of $11n_d$ protecting a Chern number $C=\pm 1$. Emergent ferromagnetic long-range Ising interactions $r^{-\gamma }$ with $2<\gamma <3$ between defect chiralities lead to a finite-temperature $T_c$ phase transition into the chiral spin liquid. The $T_c$ is proportional to $n_d$ and diverges when $\gamma \to 2$. We also consider additional solvable impurity potentials and find that $\gamma$ can be reduced to below 2.3 and correspondingly enhance $T_c$. Our results offer applications to 2D Dirac cone systems with a finite density of fluctuating Ising magnetic impurities and to identifying spin liquids with lattice defects.

The quantum behavior of light particles in solids gives rise to phenomena that cannot be captured by a classical description. We show that muon spin spectroscopy ($\mu \mathrm{SR}$), when paired with a quantum-mechanical treatment of the implanted muon, becomes a sensitive and direct probe of nuclear quantum effects. By modeling the muon as a spatially extended quantum particle, our approach captures strong anharmonic behavior. We demonstrate this in Zn-barlowite, which serves as a nontrivial test case due to its structurally complex lattice and the presence of both fluorine and hydroxyl groups. Our results establish a route for extracting nuclear quantum signatures from $\mu \mathrm{SR}$ data and open different opportunities for studying light nuclei such as hydrogen and lithium in systems where quantum fluctuations shape structure and function.

The superconducting gap is a characteristic feature of high-$T_{\mathrm{c}}$ superconductors and provides crucial information on the pairing mechanism underlying high-temperature superconductivity. Here, we employ high-resolution resonant inelastic x-ray scattering (RIXS) at the Cu $L_3$ edge to investigate the superconducting gap in the overdoped cuprate ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{Ca}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{10+\delta }$ ($T_{\mathrm{c}}=107\mathrm{K})$. By analyzing antisymmetrized, temperature-dependent RIXS spectra over a range of in-plane momentum transfers, we observe a clear suppression of low-energy spectral weight below $T_{\mathrm{c}}$, indicative of superconducting-gap formation. This suppression is most pronounced at small momentum transfers $\left[\right|{\mathit{q}}_{\parallel }|\le 0.18$ r.l.u. (reciprocal lattice units)] and corresponds to a gap size of approximately $2{\mathrm{\Delta }}_0\sim 130$ meV. Comparison with theoretical calculations of the momentum-dependent charge susceptibility supports a $d$-wave symmetry of the superconducting gap, while an isotropic $s$-wave gap fails to reproduce key experimental features. These findings establish RIXS as a powerful, bulk-sensitive probe of superconducting-gap symmetry and highlight its utility for studying materials beyond the reach of surface-sensitive techniques such as ARPES and STM.

Building on recent advances in reduced density matrix theory, we develop a geometric framework for describing strongly correlated lattice bosons. We first establish that translational symmetry, together with a fixed pair interaction, enables an exact functional formulation expressed solely in terms of momentum occupation numbers. Employing the constrained-search formalism and exploiting a geometric correspondence between $N$-boson configuration states and their one-particle reduced density matrices, we derive the general form of the ground-state functional. Its structure highlights the omnipresent significance of one-body $N$-representability: (i) The domain is exactly determined by the $N$-representability conditions; (ii) at its boundary, the gradient of the functional diverges repulsively, thereby generalizing the recently discovered Bose-Einstein condensate (BEC) force; and (iii) an explicit expression for this boundary force follows directly from geometric arguments. These key results are demonstrated analytically for few-site lattice systems, and we illustrate the broader significance of our functional form in defining a systematic hierarchy of functional approximations.

Spin-orbit Mott insulators with the $t_{2g}^5$ electron configuration are promising platforms for the Kitaev spin liquid, yet fine-tuning of their crystal structures is essential to suppress non-Kitaev interactions. Here, we investigate the local electronic structures of the ilmenite iridates $A{\mathrm{IrO}}_3$ ($A=\mathrm{Mg},\mathrm{Zn},\mathrm{Cd}$) and the hyperhoneycomb $\beta \text{−}{\mathrm{ZnIrO}}_3$ using Ir $L_3$-edge resonant inelastic x-ray scattering (RIXS). Multiplet analysis of the RIXS spectra reveals a systematic evolution of the crystal field and intraionic interaction parameters upon chemical substitution at the $A$ site. We observe an enhancement of the trigonal distortion with increasing $A$-site ionic radius, providing a microscopic explanation for the deviation from the ideal $J=1/2$ state and the antiferromagnetic interactions identified in ${\mathrm{CdIrO}}_3$. Furthermore, the local multiplet parameters of ilmenite ${\mathrm{ZnIrO}}_3$ and hyperhoneycomb $\beta \text{−}{\mathrm{ZnIrO}}_3$ are found to be nearly identical, demonstrating that their different magnetic ground states are primarily governed by their distinct lattice structures rather than by single-ion properties. These findings establish a solid foundation for understanding how local crystal-field distortions control the magnetic Hamiltonian in Kitaev-candidate materials.

Using the Zwanzig projection-operator formalism, we derive a causal two-point spatiotemporal kernel for heat conduction, defined microscopically as a space-resolved equilibrium heat-flux time-correlation function, that encodes temporal memory, spatial nonlocality, and material heterogeneity on equal footing. Classical diffusion, nonlocal transport, and hydrodynamic models emerge as controlled asymptotic limits of this kernel, providing a unified constitutive description across diffusive, quasiballistic, and hydrodynamic regimes. Interfacial heat transfer is incorporated through a spatially resolved kernel formulation, in which the conventional Kapitza resistance arises as a coarse-grained limit. The kernel admits a spatiotemporal Green–Kubo representation and can, in principle, be evaluated from atomistic simulations for bulk media, providing a direct connection between microscopic dynamics and continuum transport without empirical closure. For crystalline solids, we derive explicit kernel forms in the hydrodynamic and attenuated-streaming limits and introduce a hybrid reduction that captures the coexistence of collective and quasiballistic transport. For disordered harmonic solids, the framework recovers a spatial diffusion kernel consistent with the Allen–Feldman limit. To illustrate the theory, we construct the kernel for silicon at room temperature within the relaxation-time approximation and apply it to transient thermal-grating configurations. Spatial nonlocality associated with the phonon mean-free-path distribution is the primary source of deviation from Fourier transport under these conditions, while temporal memory mainly influences short-time dynamics. These findings identify the spatiotemporal kernel as a unifying constitutive descriptor whose coarse-grained limits recover conventional transport coefficients.

The coupling of atomic vibrations to electronic excitations—traditionally understood to be a source of energy loss in semiconductors—has recently been explored in photosynthetic light harvesting as a means to circumvent dissipation by harnessing quantum vibronic coherence. Motivated by recent photocurrent measurements of vibronic sidebands in ${\mathrm{WSe}}_2/{\mathrm{MoSe}}_2$ optoelectronic devices [F. Barati et al., Nano Lett. 22, 5751 (2022)], we present a nonperturbative theoretical framework for phonon-assisted absorption in van der Waals heterostructures. Using a polaron transformation, a closed-form expression for the optical absorption spectrum at arbitrary temperatures is presented. Our model includes both intraband and interband electron–phonon coupling. Detailed analysis shows that the observed periodic sidebands originate from the strong coupling between interlayer excitons and nearly dispersionless optical phonon modes. By comparing two limiting cases, one involving only intraband couplings and the other incorporating coherent interband processes, we show that interband phonon-assisted transitions are needed to account for the observed data. Beyond enabling the direct estimation of vibronic coupling strengths from spectroscopic data, these findings have profound consequences for our understanding of optical and optoelectronic responses: coherent interband coupling of atomic vibrations to excitons is essential to quantifying photoresponse in transition metal dichalcogenide heterostructures.

Altermagnetism (AM), the recently discovered third class of collinear magnetic order, is characterized by a nonrelativistic momentum-dependent spin-split electronic structure with compensated zero net magnetization. It can arise from the conventional antiferromagnetism by introducing local anisotropy on the two opposite-spin sublattices, either through structural changes in local crystallographic symmetry or spontaneous emergence of local staggered orbital order from electron correlations in multi-orbital systems. Here, we demonstrate on the two-dimensional square lattice that a $d$-wave AM can emerge spontaneously in the single-orbital extended Hubbard model, without invoking crystallographic anisotropy and multi-orbital physics. We carry out mean-field studies on the concrete single-orbital $t\text{−}U\text{−}V$ model, with $U$ and $V$ the on-site and nearest-neighbor Coulomb interactions, obtaining the mean-field ground states, analyzing their properties, and determining the phase diagram in the $U\text{−}V$ plane. The $d$-wave AM with interesting spin-transport behavior is found to be stabilized in a wide region of the phase diagram when the system is doped away from half filling, actualized by the coexistence of on-site antiferromagnetic order and complex $d$-wave nearest-neighbor spin bond orders. Our findings provide an alternative route to achieve AM and substantially expand the range of candidate AM materials.

Electrons in two-dimensional electron gases in the presence of an out-of-plane magnetic field propagate along the edge with a high velocity of the order of the Fermi velocity. Under microwave and terahertz radiation, photon absorption by these electrons provides a pathway to realizing sensitive radiation detection. Here, we develop a detailed quantum theory of the photocurrent generated in such a system by an incident electromagnetic wave and propose an experimental geometry for observing the predicted phenomenon. By using suitably arranged radiation confinement structures, a strong photocurrent generation efficiency can be obtained. We also demonstrate that the resulting photoresponse in III-V semiconductor structures can be orders of magnitude higher than that measured in graphene.

We investigate the dynamics of ferroelectric textures driven by polarization currents. We show that ferrons, the quanta of collective polarization excitations, provide an exotic driving mechanism for domain wall (DW) dynamics, compared with their magnonic counterparts. By mapping the linear polarization dynamics of a DW onto a Schrödinger-like problem with a Pöschl-Teller potential, we show that polarization waves are fully transmitted and therefore do not exert a net force on the DW in the linear regime. However, intrinsic nonlinearities give rise to a negative radiation pressure that pulls the DW toward the source. This mechanism allows efficient DW control by optical excitation and temperature gradients with application potential in ferroelectric memory and logic devices.