We analyze the spectrum of collective modes in a superconductor, in which pairing is mediated by long-range nematic fluctuations. Previous experimental and theoretical studies have found that a superconducting gap in such a system is highly anisotropic and at any finite $T<T_c$ vanishes on four arcs of the Fermi surface even when the pairing symmetry is $s$ wave ($s^{+-}$ between hole and electron pockets). We derive the expression for the pair susceptibility $\chi (\mathbf{q},\mathrm{\Omega })$ at finite momentum $\mathbf{q}$ and frequency $\mathrm{\Omega }$ deep in the superconducting phase. We analyze the spectral function, $\text{Im}\chi (\mathbf{q},\mathrm{\Omega })$, and its pole structure in transverse (phase) and longitudinal (amplitude) channels and compare the results with those of a conventional $s$-wave superconductor. We find that the analytic structure of the pair susceptibility in both channels is qualitatively distinct from that in a BCS superconductor. This gives rise to a highly unconventional dispersion of phase and amplitude collective modes.

Solving the quantum many-body ground-state problem remains a central challenge in computational physics. In this context, the variational Monte Carlo (VMC) framework based on projected entangled-pair states (PEPS) has witnessed rapid development, establishing itself as a vital approach for investigating strongly correlated two-dimensional systems. However, standard PEPS-VMC algorithms predominantly rely on sequential local updates. This conventional approach often suffers from slow convergence and critical slowing down, particularly in the vicinity of phase transitions or within frustrated landscapes. To address these limitations, we propose an efficient autoregressive row-wise sampling algorithm for PEPS that enables direct, rejection-free sampling via single-layer contractions. By utilizing autoregressive single-layer row updates to generate collective, nonlocal configuration proposals, our method significantly reduces temporal correlations compared to local Metropolis moves. We benchmark the algorithm on the two-dimensional transverse-field Ising model and the quantum spin glass. Our results demonstrate that the row-wise scheme effectively mitigates critical slowing down near the Ising critical point. Furthermore, in the rugged landscape of the quantum spin glass, it yields improved optimization stability and lower variational energies. These findings indicate that single-layer autoregressive row updates provide a flexible and robust improvement to local PEPS-VMC sampling and may serve as a basis for more advanced sampling schemes.

We introduce a qudit-native framework for engineering rich and robust discrete time crystals (DTCs) by leveraging their internal multilevel structure. Unlike in qubit systems, qudit-based DTCs exhibit distinct dynamical mechanisms that arise only in multilevel systems, as supported by a dressed normal-form analysis in the heating-suppression regime. These mechanisms are manifested in representative systems: we show that subspace-selective embedded kicks stabilize higher-order subharmonic responses and suppress thermalization, as demonstrated in spin-1 chains; in spin-3/2 systems, extending embedded kicks to more levels enables different level partitions and reveals that DTC robustness is dictated by the symmetry of the partition; and in spin-2 platforms, we realize concurrent period-doubled and period-tripled DTCs under a unified drive. These findings establish a systematic, hardware-efficient methodology for designing stable and multifunctional Floquet phases of matter on modern qudit-based quantum processors.

Non-Hermitian jumps, manifested as abrupt wave-packet relocations arising from mode competition between spatially separated localized eigenmodes with different imaginary eigenenergies, constitute a unique dynamical phenomenon absent in Hermitian systems. These jumps are commonly thought to require strong non-Hermitian disorder to generate such competing eigenmodes. Here, using a parity-time ($\mathcal{PT}$)-symmetric Su–Schrieffer–Heeger model with Hermitian off-diagonal disorder and balanced onsite gain and loss, we show that reduced lattice connectivity allows non-Hermitian jumps to emerge even in the presence of weak disorder. Furthermore, when the disorder-induced spread of the hopping parameters overlaps with both $\mathcal{PT}$-symmetric and $\mathcal{PT}$-broken phases, wave dynamics undergo a transition from localized oscillations to non-Hermitian jumps. Our results demonstrate how the interplay of $\mathcal{PT}$ symmetry and disorder shapes wave dynamics, providing a pathway to programmable and robust directional transport in non-Hermitian systems, with potential applications in photonics, quantum information, and signal processing.

Rare-earth-based frustrated magnets have attracted significant attention as excellent candidates for magnetic refrigeration operating at subkelvin temperatures. Herein we investigate the magnetic ground states and low-temperature magnetocaloric effect (MCE) of frustrated Shastry-Sutherland ${\mathrm{Gd}}_2{\mathrm{Be}}_2\mathrm{Ge}{\mathrm{O}}_7$ (GBGO) and Lu-diluted ${\left({\mathrm{Gd}}_{0.36}{\mathrm{Lu}}_{0.64}\right)}_2{\mathrm{Be}}_2\mathrm{Ge}{\mathrm{O}}_7$ (GLBGO) compounds, both of which possess spin $S=7/2$ moment. Compared to the isostructural $S_{\mathrm{eff}}=1/2$ analog ${\mathrm{Yb}}_2{\mathrm{Be}}_2\mathrm{Ge}{\mathrm{O}}_7$ (YBGO), GBGO exhibits a volumetric entropy density ($S_V$) approximately three times larger ($429\mathrm{mJ}{\mathrm{K}}^{-1}\mathrm{c}{\mathrm{m}}^{-3}$ versus $149\mathrm{mJ}{\mathrm{K}}^{-1}\mathrm{c}{\mathrm{m}}^{-3}$), while GLBGO shows a comparable $S_V$ ($158\mathrm{mJ}{\mathrm{K}}^{-1}\mathrm{c}{\mathrm{m}}^{-3}$ versus $149\mathrm{mJ}{\mathrm{K}}^{-1}\mathrm{c}{\mathrm{m}}^{-3}$). Magnetic and specific heat measurements reveal that GBGO forms an antiferromagnetic ordered state at $T_N=0.85$ K, whereas GLBGO shows spin freezing behavior below $T_f\sim 0.22$ K. Analysis of magnetic entropy $S_M$ ($T, B$) reveals that GBGO yields a substantially larger volumetric entropy change (–$\mathrm{\Delta }{S}_M$) in temperature windows of 0.6–2 K though it is outperformed by YBGO below $\sim 0.6$ K. However, YBGO can realize much lower minimum temperature ($T_{\min }$) than both GBGO and GLBGO. Importantly, a critical entropy value $S_V\sim 185\mathrm{mJ}{\mathrm{K}}^{-1}\mathrm{c}{\mathrm{m}}^{-3}$ is identified through comparison with other Gd/Yb-based subkelvin magnetic refrigerants. Above this threshold, Gd-based magnets have an advantage in achieving larger MCE at temperatures near or above their $T_N$; below it, Yb-based ones possess better subkelvin cooling performance featuring larger MCE and lower $T_{\min }$.

${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ and ${\mathrm{MnBi}}_4{\mathrm{Te}}_7$ are antiferromagnetic topological insulators belonging to the ${\mathrm{MnBi}}_{2n}{\mathrm{Te}}_{3n+1}$ series, where structural layering provides a natural route to tune magnetic interaction in van der Waals magnets. Despite extensive interest in their topological properties, how the insertion of ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ quintuple layers modifies magnetic critical fluctuations near the antiferromagnetic transition remains unresolved. Here, we combine scanning tunneling microscopy (STM), critical scaling analysis and magnetocaloric measurements to directly correlate real-space structures with magnetic criticality. STM reveals atomically flat septuple-layer terraces in ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$, whereas ${\mathrm{MnBi}}_4{\mathrm{Te}}_7$ displays coexisting septuple and quintuple-layer terminations reflecting its alternating stacking sequence. ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ exhibits robust three-dimensional Ising-like critical behavior together with a distinct low-temperature first-order transition. In contrast, ${\mathrm{MnBi}}_4{\mathrm{Te}}_7$ displays crossover-dominated criticality arising from weakened interlayer exchange and competing magnetic phases. Correspondingly, the magnetocaloric response differs significantly between the two compounds. ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ shows dual-type magnetocaloric behavior with a sharp field-induced sign reversal of the isothermal magnetic entropy change ($-\mathrm{\Delta }{S}_M$). It exhibits both inverse ($-\mathrm{\Delta }{S}_M<0$) and conventional ($-\mathrm{\Delta }{S}_M>0$) magnetocaloric effects. In contrast, ${\mathrm{MnBi}}_4{\mathrm{Te}}_7$ shows only conventional magnetocaloric response with a broad positive entropy peak. These results establish structural layering as a key parameter governing magnetic critical fluctuations and magnetocaloric behavior in ${\mathrm{MnBi}}_{2n}{\mathrm{Te}}_{3n+1}$ topological magnets.

FeSe stands out among iron-based superconductors due to its extended nematic phase without the onset of long-range magnetic order. While strain-dependent electrical resistivity has been extensively explored to probe nematicity, its influence on magnetotransport properties remains less understood. In this work, we present measurements of the magnetoelastoresistivity in FeSe as a function of temperature and applied magnetic field. Using a minimal multiband Boltzmann model for transport we derive analytical expressions that capture the magnetic behavior of the whole set of experimental data both in the paramagnetic and in the nematic phase. These findings indicate that a multiband framework can robustly describe the magnetoelasto-transport properties in FeSe and arguably in other iron-based superconductors.

Exploring the chemistry of materials at high pressures enables the discovery of previously unknown, but frequently exotic, compounds. We systematically searched for all thermodynamically stable Sr-C compounds under pressure (up to 100 GPa) using the ab initio evolutionary crystal structure prediction method. Our search led to the discovery of hitherto unknown phases of ${\mathrm{SrC}}_3, {\mathrm{Sr}}_2{\mathrm{C}}_5, {\mathrm{Sr}}_2{\mathrm{C}}_3, {\mathrm{Sr}}_2\mathrm{C}, {\mathrm{Sr}}_3{\mathrm{C}}_2$, and SrC. The discovered crystal structures feature a variety of different carbon environments ranging from isolated C anions and C dimers to exotic polyatomic carbon anions, including chains, stripes, and infinite ribbons consisting of pentagonal ${\mathrm{C}}_5$ and hexagonal ${\mathrm{C}}_6$ rings. The dynamical stability of all predicted compounds is confirmed by phonon calculations. Bader analysis unravels very diverse chemistry in these compounds, and bonding patterns in some of them can be described using the Zintl-Klemm rule.

We investigated the thermoelectric effects of the Dirac electron system ${\mathrm{Ag}}_2\mathrm{Te}$ under magnetic field. Our analysis based on the Boltzmann semiclassical model associated the disorder with the unconventional magnetic field responses such as linear magnetoresistance, linear Nernst effect, steplike Nernst effect, and sign change in Nernst effect. The analysis also revealed the impurity band near the Fermi energy. We simultaneously clarified the serious impact of the thermal Hall effect on the measurement of the Nernst effect, and we proposed the definitive solution. Our careful measurement and analysis will be the standard for the thermoelectric study under magnetic field.

Understanding the microscopic mechanisms of energy exchange between lattice and spin degrees of freedom is fundamental to the development of next-generation spintronic and magnonic devices. Here we employ transient absorption (TA) spectroscopy to investigate the nonequilibrium spin dynamics in antiferromagnetic cobalt oxide films following photoexcitation. We demonstrate that the TA features associated with the $d\text{−}d$ transitions of transition metal ions act as an effective thermometer for tracking transient spin temperature. Below the Néel temperature, we observe a slow, nanosecond-scale rise in spin temperature, which we attribute to energy transfer from the photoheated lattice to the spin subsystem. Our analysis reveals that the spin-lattice coupling coefficient follows a $T^3$ power-law dependence, consistent with a microscopic model where the energy transfer rate is governed by the thermal occupancy of magnons in the presence of a large hot phonon population. These findings establish $d\text{−}d$ transitions as a sensitive spectroscopic probe for nonthermal spin dynamics and provide fundamental insights into the scaling laws governing spin-lattice equilibration in antiferromagnetic oxides

Magnetic pyrochlore oxides exhibit various unconventional electronic phases and excitations due to geometric frustration. Recently, a collective magnetic excitation was reported in Raman spectroscopy on a pyrochlore ruthenate ${\mathrm{Nd}}_2{\mathrm{Ru}}_2{\mathrm{O}}_7$. However, its origin remains unclear as the Ru magnetic ground state has been controversial due to sample quality and inconsistent experimental interpretations. Here, we performed neutron diffraction measurements on a high-quality polycrystalline sample with a nearly absent magnetic impurity phase. Magnetic susceptibility and neutron diffraction measurements reveal an intrinsic Ru magnetic transition at around 145.6 K, whereas a controversial magnetic anomaly at around 21 K is suppressed in our sample, indicating that the latter is dominantly from the magnetic impurity phase. Below 145.6 K, well-defined magnetic Bragg peaks from Ru moments were observed, implying well-formed spin-spin correlations. Magnetic refinements combined with magnetic space group analysis revealed competing Ru magnetic structures, supported by density functional theory calculations. Our results suggest that the collective Raman signal may arise from competing Ru magnetic orders. Order-by-disorder and energetic scenarios are discussed as selection mechanisms for the Ru magnetic ground state. This study provides crucial insights into the search for possible order-by-disorder and topological magnetic properties in a less-studied spin-1 pyrochlore.

Ultrafast spin dynamics in ferrimagnets underpin high-speed spintronic devices that combine rapid magnetic dynamics with finite magnetization for electrical detection. Here we investigate the ultrafast magnetization and lattice dynamics in ferrimagnetic antiperovskite ${\mathrm{Mn}}_4\mathrm{N}$ epitaxial thin films on ${\mathrm{SrTiO}}_3$ using time-resolved magneto-optical Kerr spectroscopy. Structural characterization reveals a tetragonal distortion induced by epitaxial tensile strain, which stabilizes strong perpendicular magnetic anisotropy. Following femtosecond optical excitation, the magnetization exhibits an ultrafast demagnetization with a characteristic time of $\sim 190\mathrm{fs}$, followed by two recovery components with different timescales, which suggest temporally distinct responses of the inequivalent Mn sublattices. Field-independent demagnetization dynamics indicate that the process is governed primarily by intrinsic electronic scattering rather than external magnetic perturbations. We further demonstrate gigahertz spin precession frequencies and remarkably low Gilbert damping ($\sim 0.02$). In addition, coherent acoustic phonon modes in the tens-to-hundreds of GHz range are detected, revealing temperature-dependent lattice softening. These results provide insight into the coupled spin-lattice dynamics of rare-earth-free ferrimagnetic nitrides and highlight ${\mathrm{Mn}}_4\mathrm{N}$ as a promising platform for ultrafast spintronic applications.

We demonstrate that the infinite-$U$ triangular-lattice Hubbard model supports a superconducting state built from tightly bound Cooper pairs composed of two holes and one magnon ($2h1m$). Building on the seminal prediction of repulsively bound $2h1m$ states, we show that next-nearest-neighbor hopping $t_2$ coherently mixes symmetry-related configurations, stabilizing an $s$-wave bound state with substantial binding energy and a light effective mass. Large-scale density matrix renormalization group calculations at finite doping reveal, over a finite magnetic-field window, a magnetization plateau with one magnon per pair of doped holes and quasi-long-range superconducting order characterized by algebraically decaying $2h1m$ correlations. Our results establish a kinetically driven superconducting phase of composite magnonic Cooper pairs and provide directly measurable signatures for moiré Hubbard materials and ultracold-atom simulators.

We develop a variational method for interacting surface systems with higher-form global symmetries. As a natural extension of the conventional second-quantized Hamiltonian of interacting bosons, we explicitly construct a second-quantized Hamiltonian formulated in terms of a closed surface operator $\widehat{\varphi }\left[C_p^{}\right]$ charged under a $p$-form global symmetry. Applying the variational principle, we derive a functional Schrödinger equation analogous to the Gross–Pitaevskii equation in conventional bosonic systems. In the absence of external forces, the variational equation admits a uniform solution that is uniquely determined by a microscopic interaction potential $U\left({\psi }^{*}\psi \right)$ and the chemical potential. This uniform solution describes a uniform gas of bosonic surfaces. Using the obtained energy functional, we show that low-energy fluctuations contain a gapless $p$-form field $A_p^{}$ when the $p$-form global symmetry is $\mathrm{U}\left(1\right)$, whereas the $p$-form field becomes massive for discrete symmetries, whose low-energy limit is described by a BF-type topological field theory. As a consequence, the system exhibits Abelian topological order with anyonic surface excitations. In the presence of external forces, however, solving the functional equation in full generality remains challenging. We argue, however, that the problem reduces to solving the conventional Gross–Pitaevskii equation when external forces act separately on the center-of-mass and relative motions. In addition, we present analytic solutions for topological defects as analogs of vortex and domain-wall solutions in conventional bosonic systems. Finally, as a concrete microscopic model, we study a ${\mathbb{Z}}_N^{}$ lattice gauge theory and show that our variational method correctly reproduces the ground states in the analytically solvable limits.

${\mathrm{K}}_2{\mathrm{Ni}}_2{\left({\mathrm{SO}}_4\right)}_3$ is a member of the langbeinite family, consisting of two intertwined $S=1$ trillium lattices, of which one is strongly coupled (strong-TL) and the other is weakly coupled (weak-TL). Further intertrillium interactions give rise to a highly frustrated Heisenberg Hamiltonian. Despite ordering at low temperatures, ${\mathrm{K}}_2{\mathrm{Ni}}_2{\left({\mathrm{SO}}_4\right)}_3$ lies close in parameter space to a spin-liquid region that surrounds the tetratrillium limit, where each triangle belonging to the strong-TL turns into a tetrahedron by connecting to a single spin from the weak-TL. Here, we compare the experimentally determined magnetization process using pulsed magnetic fields up to 40 T with classical Monte Carlo calculations, uncovering a series of phase transitions at both low and intermediate fields. Furthermore, we reveal a signature of a $2/3$ magnetization plateau consisting of a $1/3$ phase on the strong-TL and a fully polarized phase on the weak-TL. Although in the classical limit no plateau is expected, we find a very prominent dome structure reflecting the tendency of the system to stabilize this particular spin configuration. The presence of a dome leads to a reentrant phenomenon in which the system recovers the Hamiltonian symmetries when increasing the magnetic field. Finally, we show that this plateau-like phase is also present in the classical Heisenberg model on the single trillium and tetratrillium lattices, indicating its possible presence in the large family of double-trillium langbeinite compounds. Our findings motivate future studies on the presence of the plateau phase in the quantum limit of both trillium and double-trillium materials within the langbeinite family.

The effective mass approximation is widely used across models of carrier transport, optical response, and excitons in semiconductors and insulators, but its validity hinges on the assumption that the band dispersion $E_n\left(\mathbf{k}\right)$ at the relevant extremum is analytic. We prove that analyticity holds at any nondegenerate extremum for Kohn-Sham density functional theory (DFT) with local or hybrid exchange-correlation functionals, for Hartree-Fock, and for band-edge $G_0{W}_0$ quasiparticle energies in gapped systems. Band nonanalyticity (or warping) in these settings is therefore intrinsically tied to degeneracy. We then use group theory to determine the symmetry-allowed form of the effective mass tensor for each of the 32 crystallographic point groups, providing a stringent consistency check on first-principles calculations. As a representative application, we show that the electron and hole effective masses at the $K$ point of monolayer ${\mathrm{MoS}}_2$ must be strictly isotropic at the DFT and $G_0{W}_0$ levels.

Understanding how electronic transport evolves from localized to itinerant regimes in correlated cluster solids remains an important challenge in condensed-matter physics. Here, we investigate the pressure-dependent transport properties of the lacunar spinel ${\mathrm{GaNb}}_4{\mathrm{Se}}_8$, a cluster Mott insulator at ambient conditions. At ambient pressure, the resistivity follows Efros-Shklovskii variable-range hopping, indicating Coulomb gap–controlled carrier localization. A pressure-induced electronic delocalization process begins at low pressures (∼5 GPa), as evidenced by the continuous suppression of room-temperature resistance. Upon further compression, the system undergoes a broad insulator-to-metal-like crossover in low-temperature transport, culminating in a fully metallic-like ground state at ∼17–18 GPa. In contrast, the crystallographic transition from the cubic phase to the monoclinic $C2$ phase starts at ∼20 GPa and ends near ∼32 GPa, demonstrating that the pressure-induced electronic evolution is completed before the onset of long-range structural symmetry breaking. At higher pressures, superconductivity (with a superconducting coherence length ξ(0) ≈ 80–90 Å) emerges from a pressure-induced metallic-like regime. These results establish ${\mathrm{GaNb}}_4{\mathrm{Se}}_8$ as a platform for studying correlation-driven evolution of electronic transport in cluster-based solids.

We report a machine-learned interatomic potential for uranium dioxide with xenon gas, as well as a machine-learned potential for uranium dioxide. Training datasets were constructed by leveraging a combination of density functional theory calculations with a Hubbard $U$ correction and molecular dynamics simulations. Query-by-committee active learning procedures further automated the augmentation of training datasets. The efficacy of employing an equivariant message-passing neural network for iterative potential fitting was demonstrated by reproducing $\mathrm{DFT}+U$-level forces and energies, despite the training datasets being much smaller than those for recently reported uranium dioxide MLPs. We found that our machine-learned potential for ${\mathrm{UO}}_2$ achieves strong agreement with experimentally observed thermophysical and thermomechanical properties across a temperature range 300–3000 K. Our second machine-learned potential for uranium dioxide with xenon successfully replicates reference $\mathrm{DFT}+U$ incorporation energies of xenon into various lattice sites. We also employed this MLP to calculate migration barriers for xenon diffusion via tetravacancy defect cluster mechanisms. The superlative ability of these machine-learned potentials to capture the behavior of uranium dioxide with xenon inclusion across a range of temperatures and defect chemistries lays the foundation for larger-scale molecular dynamics simulations of fission gas transport through uranium oxide fuel matrices.

The Hatsugai-Kohmoto (HK) model is an exactly solvable electronic lattice model where the interaction between electrons with opposite spin is diagonal in momentum space. We generalize the HK model by introducing momentum-mixing Landau interactions. Within a self-consistent mean-field analysis we find that the ground state of this model exhibits a partially flat energy band, in agreement with the fermion condensation scenario proposed by Khodel and Shaginyan [JETP Lett. 51, 553 (1990)]. Inspired by Anderson's pseudospin formulation of Bardeen-Cooper-Schrieffer theory, we show that the HK model with Landau interactions can be mapped onto a generalized Ising model where each site of the reciprocal lattice hosts two Ising spins. In the pseudospin picture the emergence of a partially flat electronic band corresponds to the smoothing of a magnetic domain wall. Moreover, guided by the pseudospin picture, we propose an exactly solvable variant of the HK model which has a unique ground state for all densities.

Image-potential surface states are simple model systems, where spin-dependent effects can be studied in view of spintronic applications. The Rashba effect in surface states at high-$Z$ materials is related to both the strong spin-orbit interaction in heavy atoms and the orbital angular momentum arising from the inversion-symmetry breaking at the surface. Our study on image-potential states at ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ and ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ showcases that the orbital angular momentum causes an intrinsically reversed Rashba parameter ${\alpha }_{\mathrm{R}}\approx -100\mathrm{meV}\AA$, i.e., a reversed spin splitting compared with the prototypical Rashba-split Au(111) crystal-induced surface state. We present a consistent picture of spin-resolved experimental data from inverse photoemission and three-photon photoemission together with calculations from density-functional theory and many-body perturbation theory.