We study the spin Hall effect in two-dimensional topological insulators with "Mexican hat" dispersion and a ring-shaped Fermi surface which are formed due to the band inversion. Electron transitions between different isoenergetic contours and the quantum metric of band states play an important role in the transport properties of such materials, since they largely determine the spatial distribution of the electron charges screening the impurity potential and the scattering probability [Phys.B, 719, 417942 (2025)]. Here we study a spin-dependent skew scattering, which is enabled by the second-order scattering processes, and show that the extrinsic spin-Hall current (SHC) can significantly exceed the intrinsic SHC arising from the Berry curvature. Furthermore, due to Mexican-hat dispersion, the SHC exhibits a very unusual dependence on the Fermi energy ($E_F$). The extrinsic SHC reaches a maximum at some $E_F$, then decreases with increasing $E_F$ and can even change a sign. This complicated behavior reflects an interplay of energy dependencies of such important factors as probabilities of inter- and intra-contour transitions, as well as different electron velocities in two contours.
Conflicting reports exist on the ground state of the intermetallic compound CeRhSn$_2$. This can be rooted in the sawtooth-like arrangement of two inequivalent Ce sites in the unit cell, which suggests potential geometric magnetic frustration. To resolve, we conducted a comprehensive study on high-quality single crystals of CeRhSn$_2$ by means of magnetization ($M$), specific heat ($C_p/T$), and resistivity ($\rho$). The system exhibits strong magnetic anisotropy, confirming the $b$-axis as the easy magnetic axis. We establish three successive transitions, an AFM order at $T_{N} = 3.65$K, a first-order FM order at $T_{C} = 1.7$K and final transition, at $T = 1.5$K. The transition temperatures are highly field-directional dependent: in a magnetic field, the lowest transition is immediately suppressed while $\mathbf{H} \parallel b$ rapidly merges $T_{C}$ and $T_{N}$ into a single second-order transition. Conversely, $\mathbf{H}\parallel c$ suppresses the FM order and reduces $T_{N}$. Additional ab initio calculations affirm the FM ground state of CeRhSn$_2$. The observation of an enhancement of the Sommerfeld coefficient ($\gamma = 76.5$mJ/mol$\cdot$K$^2$) may arise from geometric frustration, but it is most consistently attributed to weak Kondo hybridization as frustration cannot be conclusively established through our data.
We have studied the (110) surface of Fe$_3$O$_4$ single crystals by means of spin-polarized low-energy electron microscopy (SPLEEM). After preparation by sputtering and annealing a well defined reconstructed surface was achieved, composed of rows aligned in the [010] direction. By acquiring SPLEEM images along different spin directions the vector magnetization was mapped on the surface, both at room temperature and at a temperature well below the Verwey transition. At room temperature, domains were observed with their magnetization aligned along the two bulk easy axes which are in the (110) surface plane. They presented 180$^\circ$, 71$^\circ$ and 109$^\circ$ N\'eel-type domain walls. Below the Verwey transition, the magnetization directions changed to regions where the magnetization was oriented along the in-plane [100] and [001] directions. Those observations can be interpreted as the presence of magnetized regions on the surface where the monoclinic $c$ axis is in-plane in the former, and regions where the $c$ is out-of-plane in an oblique direction in the latter. However, the magnetization was at all times within the surface plane, with no out-of-plane component detected.
Electron transport in solids arises primarily from two mechanisms: freely moving bulk electrons in metals, and gapless boundary states in topological insulators. Here, we report a new mechanism discovered in electrides. The topological interstitial-electron conductors (TIECs) proposed here are insulating electrides, but host interstitial electrons (IEs) distributed within crystal voids that traverse the entire unit cell. Without being tightly bound to real ions, the IEs generally experience low periodic potential barrier along the void channels. As a consequence, by applying a weak electric field sufficient to overcome the IE barriers but far below the system's dielectric breakdown threshold, one can expect that the TIECs would generate a persistent current contributed by the IEs and propagating along the void channels. We identify a family of realistic altermagnetic electrides, $A_5X_3$ ($A$ = Ca, Sr, Ba, Yb; $X$ = As, Sb), as TIECs. Remarkably, for $A_5X_3$ materials, the periodic potential barrier of the IEs along the void channels are ultralow, ranging from 13.43 to 67.96 meV per formula unit. This renders our proposal readily accessible to experimental verification. We further demonstrate that when the IEs of $A_5X_3$ undergo periodic motion along the channels, topological surface states will emerge at the boundary perpendicular to the channel direction, and continuously move across the bulk band gap. This pumping-like behaviour not only corroborates the topological nature of TIECs, but also rationalizes the finite-electric-field induced electronic transport within the band theory. Our findings expand the classification of electronic conductors, uncover unexplored transport properties of electrides, and establish a new material platform for low-power electronic devices.
Submitted on 2026-05-31, refereeing deadline 2026-06-14.
Advanced Materials, EarlyView.
Recent experimental observations in the noncentrosymmetric Weyl semimetal PtBi$_2$ indicate unconventional superconductivity hosted by topological surface states -- Weyl Fermi arcs -- with a node at the center of each arc. Focusing on these Fermi arcs, we calculate the electronically mediated pairing interaction using a Kohn-Luttinger approach and find that, in a large region of the phase diagram, the leading superconducting instability has an $i$-wave symmetry featuring precisely such an intra-arc node. We study the dependence of the leading superconducting instabilities on electronic interaction parameters and chemical potential and show that the $i$-wave state is robust to changes in the model parameters. Our results provide a possible mechanism for the observation of topological $i$-wave superconductivity on the surface of PtBi$_2$ and may have implications for the broader landscape of superconducting instabilities arising from repulsive interactions on the surfaces of Weyl semimetals.
Single electron spins can be used to encode and process information in semiconductor quantum devices. Progress has been hindered by materials challenges, such as the small energy splitting between low-lying valley states and hyperfine coupling to nuclear spins. Here we use density functional theory to optimize the valley splitting and spin dephasing time in realistic Si/SiGe heterostructures. Reductions in the Si quantum well width generally increase the valley splitting. However, in narrow quantum wells, a larger fraction of the electronic wavefunction resides in the SiGe buffer layers, which increases the hyperfine coupling with spinful $^{73}$Ge. Our work shows that Si/SiGe heterostructures with 3~--~4~nm wide quantum wells and $^{73}$Ge and $^{29}$Si concentrations of 50 ppm should support average valley splittings $E_{v}$~$$~500~$\mu$eV and spin dephasing times $T_2^*$ exceeding 15~$\mu$s assuming an effective quantum dot area of 700 nm$^2$. In addition, sharper Si/SiGe interfaces in general result in larger valley splittings and longer spin dephasing times.
Understanding the $T$-linear normal-state resistivity of cuprates remains a central physics challenge. The associated momentum relaxation rate, $\Gamma_M$, saturates near the conjectured ``Planckian" bound $\Gamma_M\sim kT/\hbar$, but the mechanism underlying the anomalous scattering remains unresolved. Here we employ nonlinear terahertz spectroscopy to systematically study La$_{2-x}$Sr$_x$CuO$_4$ across a broad temperature and doping range. We measure the normal-state third-order susceptibility, $|\chi^{(3)}|\approx 6\times10^{-9}$ m$^2$/V$^2$, among the largest in the THz regime, enabling direct access to the rarely measured electronic energy relaxation rate, $\Gamma_E$. Strikingly, $\Gamma_E$ is 10-40 times smaller than $\Gamma_M$, revealing that the scatterings responsible for momentum loss and $T$-linear resistivity do not remove appreciable energy from the electrons. While $\Gamma_M (T)$ is consistent with quasi-elastic scattering from bosonic modes above their characteristic energy scale, this is incompatible with the increasing temperature dependence of $\Gamma_E(T)$. Our results exclude phonons as the source of $T$-linear resistivity and impose strong constraints on possible mechanisms.
In this study, we employ classical molecular dynamics (MD) simulations to investigate the crystallisation kinetics of supercooled liquid palladium and relate the results to time-resolved X-ray diffraction measurements on rapidly quenched Pd thin films. Crystal nucleation and growth rates are determined over the temperature range $700$--$1150~\mathrm{K}$ ($0.38$--$0.65 T_{\mathrm{m}}$) by analysing the evolution of the microstructure during the liquid-to-crystal transition. The self-diffusion coefficient of Pd, obtained from the atomic mean-squared displacement, follows Arrhenius behaviour over the investigated temperature range, with an activation energy of $467(6)~\mathrm{meV/atom}$, consistent with available data for supercooled liquid metals. The steady-state homogeneous nucleation rate exhibits a maximum of approximately $4 \times 10^{35}~\mathrm{m^{-3} s^{-1}}$ near $0.5 T_{\mathrm{m}}$. Crystal growth occurs at velocities of the order of metres per second, with a temperature dependence consistent with diffusion-limited Wilson-Frenkel kinetics rather than the collision-limited regime. Based on multiple statistically independent simulations, a time-temperature-transformation (TTT) diagram for crystallisation onset is constructed. The TTT curve exhibits a nose near $0.5 T_{\mathrm{m}}$ and $100~\mathrm{ps}$, corresponding to a critical cooling rate for vitrification on the order of $10^{13}~\mathrm{K s^{-1}}.$ The simulations reproduce the crystallisation onset time and temperature observed in time-resolved X-ray diffraction experiments on optically molten Pd thin films quenched at $5 \times 10^{11}~\mathrm{K s^{-1}}.$ These results indicate that homogeneous, rather than heterogeneous, nucleation governs the achievable supercooling in the experimentally studied films.
Advanced Materials, EarlyView.
Superconducting domes are conspicuous features of the phase diagrams of most unconventional and high-temperature superconductors. The superconducting transition temperature ($T_{c}$) of FeSe can be dramatically enhanced with electron doping, but unlike all other high-temperature and unconventional superconductors, its full phase diagram and superconducting dome have yet to be fully explored. Here, we employ a combination of molecular beam epitaxy synthesis, alkali surface doping, in-vacuum electrical transport, and angle-resolved photoemission spectroscopy to investigate the entire superconducting dome of electron-doped FeSe, achieving a fully metallic state where superconductivity is suppressed in the heavily overdoped regime. We discover a robust scaling between $T_{c}$ and the residual resistivity ($\rho_{0}$) which holds across the entire superconducting dome, suggesting that the evolution of $T_{c}$ is heavily influenced by the evolution of the elastic scattering rate in the high-$T_{c}$ electron-doped phase. This in turn suggests that the superconducting dome in electron-doped FeSe appears to be fundamentally different than that of other unconventional superconductors where doping plays the primary role, and may be driven primarily by the sensitivity of the superconductivity to disorder.
We theoretically investigate the ultrafast generation of spin and orbital magnetism in a two-dimensional gapped Dirac system with spin-orbit coupling. This system is representative of two-dimensional hexagonal semiconductors, such as transition-metal dichalcogenides that exhibit valley-selective optical selection rules arising from the valley-contrasting magnetic texture of their band structure. Using a time-dependent density-matrix formalism, we demonstrate that circularly polarized laser pulses generate nonequilibrium magnetization under both resonant and multiphoton resonant conditions. We show that the induced spin and orbital magnetic moments can be distinctly controlled via the photon energy and polarization of the driving field. Furthermore, spin and orbital dynamics originate from fundamentally different light-matter coupling mechanisms, leading to qualitatively dissimilar temporal behaviors. The orbital magnetic moment couples directly to the external electric field, resulting in faster dynamics and pronounced Rabi-like oscillations, whereas the spin response develops gradually through spin-orbit coupling. Consequently, orbital dynamics is significantly more sensitive to electron-hole dephasing than the spin response. Our results highlight the importance of properly accounting for orbital contributions in future technologies that utilize femtosecond control of magnetism.
In a vast array of materials, including cuprates, transition metal dichalcogenides (TMDs) and rare earth tritellurides, superconductivity is found in the vicinity of short-range charge density wave (CDW) order. The crossover from long-range to short-range charge order often occurs as quenched disorder is introduced, yet it is unclear how this disorder disrupts the CDW. Here, using x-ray photon correlation spectroscopy (XPCS), we investigate the prototypical TMD superconductor CuxTiSe2 and show that disorder induces substantial CDW dynamics. We observe CDW phase fluctuations on a timescale of minutes to hours above the nominal transition temperature while the order parameter amplitude remains finite. These long timescale fluctuations prevent the system from finding the global free energy minimum upon cooling and ultimately traps it in a short-range ordered metastable state. Our findings demonstrate how correlated disorder can give rise to a distinct mechanism of domain formation that may be advantageous to the emergence of superconductivity.
Disordered superconductors represent an important area in modern condensed matter physics, where superconductivity survives even in the presence of strong electron scattering and localization effects. Understanding how disorder modifies the high-frequency electrodynamic response is not only important from physics point of view, but is also essential for developing next-generation quantum detectors and superconducting devices. In this work, we investigate the terahertz electrodynamics of disordered Ti40V60 alloy thin films using terahertz time-domain spectroscopy (THz-TDS) to understand the relationship between disorder, quasiparticle dynamics, and kinetic inductance. By analysing the complex conductivity, penetration depth and superfluid response, we show that structural disorder can be systematically used to tune the inductive response while maintaining a robust superconducting phase. Unlike conventional nitride superconductors that require tightly controlled reactive growth conditions, Ti40V60 alloys provide a simpler and more adaptable route for tuning the superconducting energy scales directly through the deposition conditions. These findings establish Ti40V60 alloys as a promising material for kinetic inductance detectors and provide useful insights into the electrodynamics of strongly disordered superconductors.
The reversible stress limit (\mathit{R}_{rev}) of second-generation high-temperature superconducting (2G-HTS) tapes is a critical performance indicator, typically characterized through uniaxial tensile testing. In practice, the accuracy of the measured Rrev value is often compromised by stress concentration induced by the voltage tap solder joint. The present study investigates the underlying interference mechanism using integrated experimental and numerical methods. Mechanistic analysis reveals that under uniaxial tensile loading, the local geometric inhomogeneity introduced by the solder joint induces an external, bending-like stress in the vicinity of the solder joint, transitioning from additional tensile stress in the zone adjacent to the joint to additional compressive stress in the zone remote from it. When the solder joint is attached to the front surface of the tape (the side closer to the superconducting layer), the superconducting layer experiences localized additional tensile stress, triggering premature damage and early \mathit{I}_{c} degradation. Consequently, an optimized back-surface soldering approach is proposed, which positions the superconducting layer in a localized compressive zone. Experimental validation demonstrates that the proposed approach effectively mitigates testing errors for various tape configurations. Notably, for the tape with a copper layer thickness of 5 {\mu}m, the measured \mathit{R}_{rev} increased from 546 MPa to 734 MPa, corresponding to a 42% increase, and moved closer to the actual value. The findings provide essential insights for the precision characterization of the electromechanical performances (EMPs) of 2G-HTS tapes.
We present a new class of topological phenomena in inhomogeneous systems arising from the adiabatic spatial embedding of parametrized families of quantum states such as charge pumps and their generalizations. We demonstrate that each topologically distinct class of these "diabolical textures" gives rise to distinct gapped states that are separated by "trap-scaling" critical points. When the texture varies sufficiently rapidly in space, the critical line terminates abruptly, producing an "unnecessary critical" surface. We demonstrate our results using a microscopic model of non-interacting fermions with a spatially embedded Thouless pump. We study its phase diagram comprehensively and establish its stability to arbitrary perturbations, including interactions, in the vicinity of the critical regions. For systems in arbitrary spatial dimensions and global symmetries, we present a framework to systematically classify diabolical textures using Kitaev's $\Omega$ spectrum conjecture.
The geometry of the CISS effect Score 0.13
Using scanning tunneling microscopy, and a careful selection of chiral molecules and anchoring groups, we systematically carried out a series of magnetoresistance experiments. We observed a reversal of the signal upon changing the magnetization direction, the molecular chirality, and the molecular orientation. The orientation of the molecules and the magnetization of the substrate are vectors, and by associating an axial vector with the molecule, the observations can be explained. Other recent experiments, among them null experiments showing no CISS related magnetoresistance can be explained using our framework. The physical interpretation is, that the polar electrical polarization of the molecule cannot play a direct role, while the axial magnetic polarization vector operator is a much more realistic candidate. This vector plays an important role in the creation of a magnetic moment in the interface between molecule and metallic lead.
Acute spectral sensitivity to boundary conditions and the formation of a generalized Brillouin zone associated with complex quasimomenta are features frequently attributed to systems with non-trivial non-Hermitian topology, showcasing the non-Hermitian skin effect. We show that, away from the thermodynamic limit, these features themselves are not uniquely tied to this phenomenon; they can similarly arise as parity-induced even-odd effects in non-Hermitian systems without skin effect. Despite an underlying generalized Brillouin zone description, wavefunctions remain delocalized. In addition, the effect can arise in skin-effect models as entirely separate distinguishable feature
Odd-Parity Magnons Score 0.12
Magnons, as charge-neutral spin excitations, can transport spin information without Joule heating and therefore offer a promising platform for low-power spintronics. However, in collinear magnets, the effective time-reversal symmetry forbids odd-parity magnon band splitting. Here we propose odd-parity magnons and establish a general mechanism for realizing them in collinear antiferromagnets. We provide a complete spin-point-group classification of odd-parity magnon splitting in two-dimensional collinear antiferromagnets by identifying the leading splitting types and their symmetry-allowed basis functions. This classification serves as a practical guide for searching for odd-parity magnons. We show that breaking effective time-reversal symmetry, for example by circularly polarized light or loop currents, can induce highly tunable $p$- and $f$-wave magnon splitting. In bilayer systems, the dynamical modulation can drive a topological magnon phase transition, accompanied by chiral edge modes and an abrupt jump in the magnon thermal Hall conductivity. Material-specific first-principles calculations further demonstrate the feasibility of this mechanism in real van der Waals antiferromagnets. Our study identifies the odd-parity magnons as a new class of spin excitations and provides a theoretical foundation for odd-parity magnons and ultrafast optically controlled topological magnonic devices.
Gapless fracton quantum spin liquids are exotic phases of matter described by higher-rank U(1) gauge theories which host gapped and immobile fracton matter excitations as well as gapless photons. Despite well-known field theories, no spin models beyond purely classical systems have been identified to realize these phases. Using error-controlled Green function Monte Carlo, here we investigate a square lattice spin-1 model that shows precise signatures of a fracton quantum spin liquid without indications of conventional ordering. Specifically, the magnetic response exhibits characteristic patterns of suppressed pinch points that accurately match the prediction of a rank-2 U(1) field theory and reveals the existence of emergent photon excitations in 2+1 spacetime dimensions. Remarkably, this type of fracton quantum spin liquid is not only identified in the system's ground state but also in generic low-energy sectors of a strongly fragmented Hilbert space.
Achieving sub-millikelvin electron temperatures in nanoelectronic devices could unveil new transport phenomena, extend quantum coherence times, and enhance the precision of quantum metrology. However, maintaining such low temperatures continuously remains a long-standing challenge. Here, we propose and simulate an on-chip cooling cycle that harnesses the entropy difference between an electron liquid (EL) and a Wigner crystal (WC) in flavor-degenerate flat-band materials. Cooling is driven by a current through a device with a locally gated region. Within this region, the charge carrier density is tuned such that a WC forms beneath the gate. As carriers transition from an EL to WC phase, their entropy increases, extracting heat and the sliding WC advects this heat along the device. The heat is then released when carriers transition back to the EL phase, which establishes distinct hot and cold regions and a steady temperature gradient over the device. Simulations show net cooling for sufficiently low current densities, typically below $1~\mathrm{nA}/\mu\mathrm{m}$, whereas Joule heating dominates at higher currents. Within the gated region, we estimate cooling powers of up to $8.4~\mathrm{aW}/\mu\mathrm{m}$ at a bath temperature of $4~\mathrm{mK}$. Our approach can achieve electron temperatures well below $1~\mathrm{mK}$ under suitable conditions, promising a route towards continuous on-chip cooling in this temperature regime. Our approach applies to any flat-band material with low-energy flavor degeneracy (valley and/or orbital) and low disorder, including gapped Bernal-stacked bilayer graphene, rhombohedral-stacked multilayer graphene, and magic-angle twisted bilayer graphene.
No-insulation (NI) and metal-insulation (MI) high-temperature superconducting (HTS) magnets require three-dimensional (3D) models to describe the current distribution around critical current defects. In this work, we design and validate the EXTRA homogenisation method, standing for explicit turn resolution with anisotropic homogenisation method. It allows 3D magneto-thermal finite-element (FE) simulations of large-scale magnets to be performed with high accuracy at a reasonable computational cost. The method combines the anisotropic homogenisation of turn-to-turn contact layers (T2TCLs) and their neighbouring winding turns with the explicit resolution of specific T2TCLs. In particular, the inner- and outermost winding turns and adjacent contact layers are explicitly resolved to properly describe the current distribution near current leads. In addition, the method is able to simulate local $J_{\textrm{c}}$ defects for a broad range of turn-to-turn contact resistances, provided the winding turns and T2TCLs next to the defect are explicitly resolved. For efficiency, the resolved T2TCLs are modelled using the surface contact approximation. The consistency of the proposed method is first verified on a 50-turn single pancake benchmark. It is shown to reproduce AC losses and temperature distributions obtained with a turn-resolved FE reference model, for both nominal operation and during thermal runaway. The computational efficiency of the EXTRA method is demonstrated with the simulation of a stack of three 150-turn pancake coils, for which computation time is reduced by a factor of up to 13 with respect to a turn-resolved FE reference model. Finally, the results of a large-scale 3D FE simulation, currently out of reach of turn-resolved models, are provided for an insert HTS magnet with 10,000 turns. The EXTRA method is open-source and input files to reproduce all results are made available.
Perturbations in moir\'e materials, such as due to substrates or strain, are common in many experiments and can significantly modify the electronic properties of the system. Here, we show that perturbations in twisted bilayer graphene tend to be transferred between the coupled Dirac cones, eventually reaching an equilibrium near the magic angle. We connect our results to experiments and show that this equilibrium behavior remains robust even when the moir\'e potential itself is perturbed. Our findings extend the notion of the magic angle to a more general regime governed by moir\'e-driven equilibrium.
Superconducting microwave circuits with and without Josephson inductances are the Swiss Army knife for many experiments and technologies from quantum information science to astrophysical particle detectors. Despite a large variety of existing circuit types, thin film materials and Josephson junction technologies, a flexible and reliable platform for high-magnetic-field and high-temperature applications is yet to be found. In this manuscript, we investigate coplanar waveguide cavities made of the high-temperature cuprate superconductor YBa$_2$Cu$_3$O$_7$ (YBCO), integrated with Josephson inductances and quantum interferometers that are generated by the controlled local irradiation of the YBCO with a focused helium ion beam. We obtain strongly flux-tunable microwave resonators, which not only display periodic interferometer oscillations of resonance frequency and decay rate, but also a superimposed Fraunhofer-like modulation pattern. The latter originates from the magnetic field tuning of the individual Josephson junction critical currents due to the out-of-plane junction barriers. It allows adjusting resonance frequency and flux responsivity independently of each other, potentially enabling tunable microwave circuits with low sensitivity to external magnetic-field noise over a broad range of frequencies. Finally, we investigate the temperature dependence of the cavities, show that they have promising characteristics up to 14$\,$K, and present a model for the junction-induced cavity losses.
Anderson localization is a phase transition between a "metallic phase", where wavefunctions are extended and delocalized in space, and an "insulating phase", where wavefunctions are completely localized. These transitions are driven by uncorrelated or quasiperiodic disorder, e.g., in the case of the Aubry-Andr\'e model. Here, I consider a family of Hamiltonians that generalizes the Aubry-Andr\'e model, obtained by replacing the position and momentum operators with an arbitrary pair of canonically conjugate operators. These models exhibit a hidden localization transition. The system transitions between phases where wavefunctions are either localized or delocalized with respect to the new canonically conjugate operators, acting as an insulator or metal in this rotated space. These canonically conjugate operators can be taken as a linear combination of position and momentum, corresponding to a "rotation" in the abstract space of canonical operators. In this case, the hidden localization transition is signaled by the simultaneous vanishing of both the inverse participation ratio (IPR) and the normalized participation ratio (NPR) in the position and momentum space in the thermodynamic limit. This identifies the emergence of multifractal states that are neither fully extensive nor localized on the lattice. Hence, the states exhibit a multifractal dimension at the hidden phase transition, while remaining extended (i.e., one-dimensional) in both momentum and position everywhere else in the parameter space. Surprisingly, I found that at the phase transition, this model Hamiltonian coincides with the lattice Hamiltonian of a massless Dirac fermion in a curved spacetime background, indicating an unexpected relation between localization transitions and analog gravity.
In the presence of spin-orbit coupling and in geometrically frustrated materials, a noncollinear treatment the magnetization density is essential. However, in density functional theory most exchange--correlation functional approximations were originally developed for locally collinear magnetization. Many practical approaches to noncollinear DFT have emerged over the past decade. However, a first-principles connection between widely used semilocal collinear functionals and their noncollinear generalizations remains lacking. In this work, a locally exact relation between collinear and noncollinear exchange--correlation functionals is derived at the level of gradient expansions within a $u(2)$ matrix representation of the energy functional. Within this framework, collinear semilocal variables naturally acquire distinct dependencies on transverse and longitudinal magnetization gradient components. The widely used Scalmani--Frisch scheme emerges as a first-order approximation. The transformation of collinear functional derivatives to noncollinear space is implemented through numerically robust $SU(2)$ rotations. A consistent description of local magnetic torques is demonstrated for the prototypical spin-frustrated Cr$_3$ cluster. The approach further extends to fully nonlocal functionals and provides a direct route towards numerically stable relativistic response calculations. The influence on magnetic properties in presence of spin-orbit coupling is illustrated through calculations of hyperfine couplings in the high-spin ground states of uranium and the uranium ion.
We explore the long-time behavior of Local Operator Entanglement entropy (LOE) in finite-size interacting integrable systems. For certain operators in the Rule 54 automaton, we prove that the LOE saturates to a value that is at most logarithmic in system size. This bound extends previous work [PRL $\textbf{122}$, 250603; Commun. Math. Phys. $\textbf{371}$, 651-688] showing LOE grows logarithmically in the early time regime, $t\ll L$, to the late time regime, $t\gg L $. However, the late-time logarithmic bound relies on a feature of Rule 54 that does not generalize to other interacting integrable systems: namely, that there are only two types of quasiparticles, and therefore only two possible values of the phase shift between quasiparticles. We present a heuristic argument, supported by numerical evidence, that for generic interacting integrable systems (such as the Heisenberg spin chain) the saturated value of the LOE is volume-law in system size.
arXiv:2512.10704v2 Announce Type: replace-cross Abstract: We consider the quantum Gibbs state of an interacting Bose gas on the 2D torus. We set temperature, chemical potential and coupling constant in a regime where classical field theory gives leading order asymptotics. In the same limit, the repulsive interaction potential is set to be short-range: it converges to a Dirac delta function with a rate depending polynomially on the other scaling parameters. We prove that the free-energy of the interacting Bose gas (counted relatively to the non-interacting one) converges to the free energy of the $\Phi^4_2$ non-linear Schr\"odinger-Gibbs measure, thereby revisiting recent results and streamlining proofs thereof. We combine the variational method of Lewin-Nam-Rougerie to connect, with controled error, the quantum free energy to a classical Hartree-Gibbs one with smeared non-linearity. The convergence of the latter to the $\Phi^4_2$ free energy then follows from arguments of Fr\"ohlich-Knowles-Schlein-Sohinger. This derivation parallels recent results of Nam-Zhu-Zhu.
The two-dimensional metallic quantum critical problem is a long-standing puzzle that is widely believed to hold the key to resolving ubiquitous non-Fermi liquid behavior in strongly correlated electronic systems. In this study, we present a non-perturbative renormalization group (RG) analysis of the metallic Ising-nematic quantum critical point in two dimensions, formulated directly around an intrinsically nonlocal infrared (IR) boson propagator. Rather than treating the anomalous dynamical critical exponent $a$ as a fixed phenomenological parameter, we regard it as an intrinsic component of the fixed-point data to be determined from the internal consistency of the low-energy patch field theory under highly anisotropic scaling dimensions ($[k_0]=a+1$, $[k_x]=2$, $[k_y]=1$). While the leading two-loop diagrammatics vanish identically due to kinematic pole configurations, our three-loop evaluation reveals a profound structural asymmetry between the sectors: the fermion self-energy and Yukawa vertex receive non-vanishing logarithmic corrections, whereas the corresponding bosonic counter-term remains strictly zero. Consequently, we find that no self-consistent, intersecting fixed-point solution for the exponent $a$ exists within the three-loop truncation, failing to reproduce the physical value of $a \approx 1.85$ observed in quantum Monte Carlo simulations. We conjecture that the cross-linked topology of the four-loop boson self-energy diagrams is exactly marginal and yields the minimal, mandatory bosonic counter-term required to restore multi-sector self-consistency. Our framework establishes a rigid multi-loop matching scheme necessary to uniquely pin down the critical exponent, and uncovers a stable phase space for field anomalous dimensions.
Magnetostriction, a fundamental phenomenon bridging magnetism and mechanics, has enabled a broad spectrum of applications. For almost two centuries, it has been mainly investigated for ferromagnets. Regarding the magnetostriction of antiferromagnets (AFMs), limitedly known examples for both conventional collinear AFMs and noncollinear AFMs predominantly exhibit non-saturating magnetic-field dependence. Herein, we report an easily saturated magnetostriction effect in a prototypical altermagnet - MnTe, which is an emerging class of collinear AFMs with special crystal symmetries. For high-quality MnTe single crystals, the magnetostriction saturates under a moderate field of ~0.7 T with an intriguing two-fold-symmetry anisotropy. First-principles calculations reveal that the saturated and anisotropic magnetostriction originates from symmetry-allowed coupling between elastic strain and its N\'eel order parameter. These findings break the traditional wisdom on antiferromagnetic magnetostriction.
Condensable algebras in 2+1d non-chiral topological orders characterize gapped boundary conditions and interfaces. Applied to the Symmetry Topological Field Theory, they allow classification of symmetric gapped phases and impose sharp constraints on possible phase transitions. A condensable algebra is specified not only by its underlying set of anyons, which end on the boundary or interface, but also by its algebra structure. We introduce the concept of twin condensable algebras, which have the same anyon decomposition, but inequivalent algebra structure. We revisit the classification of condensable algebras in $\mathcal{Z}(\text{Vec}_G^\omega)$, i.e. in group-theoretical topological orders for finite groups $G$ with anomaly $\omega$. In this context we are able to identify twin algebras that arise from different mechanisms, such as subgroup data, SPT cocycles, and symmetry actions. In particular, we construct infinite families of examples of twins from so-called Gassmann triples, and exhibit cases in which the reduced topological orders are inequivalent despite having identical anyon content. Physically, twin algebras describe distinct symmetric phases that have isomorphic spaces of ground states, but inequivalent order parameters. Such twin phases never exhibit relative spontaneous symmetry breaking, and can be used to construct phase transitions without hidden symmetry breaking, which are intrinsically beyond Landau transitions.
The regolith of rocky bodies, such as planets or asteroids, generally settles under gravity conditions different from those of Earth. The behavior of granular material is not easily scalable for different gravities. To predict these highly complex systems where cohesive inter particle forces can be comparable to gravitational forces, we need simulations and experiments. We did experiments on settling of three different granular samples in varying reduced gravities and examined their packing densities. We used a high precision linear stage to artificially induce reduced gravities inside the zero $g$ environment provided by the ZARM drop tower and observe the settling of our samples. The three samples were fine basalt with particle diameters of $1\text{-}200\,\mu$m, coarse basalt with $2\text{-}5\,$mm and glass beads with $750\text{-}1000\,\mu$m. The artificial gravities were $150,\,250,\,500,\,750$ and $1000\,$mm/s$^2$ and therefore ranged from large asteroid gravity to almost moon gravity. We saw the granular samples have higher volumes in lower gravities and therefore lower packing densities, we also saw the fine basalt be the most sensitive to changes in gravity, up to $+19.6\,\%$ in volume for $250\,$mm/s$^2$, followed by the coarse basalt particles, up to $+12.2\,\%$ for $150\,$mm/s$^2$ and the glass beads packing density being the least sensitive to changes in gravity, up to $+4.25\,\%$ for $250\,$mm/s$^2$. With these experiments we show change in volume is not solely dependent of particle size but also roughness and uniformity, we provide real life experimental data to validate theoretical works and highlight the role of cohesive forces in low gravity environments.