We theoretically investigate the physical properties of the magnetic van der Waals material GdGaI. Using first-principles calculations, we compute the phonon dispersion of GdGaI and show no imaginary phonons, suggesting that phonon-driven phase transitions are unlikely to occur in GdGaI. Our band calculation reveals that the electronic bands near the Fermi energy are composed of Gd $5d$ and Ga $4p$ orbitals. We construct a tight-binding model that incorporates the Gd $5d$ and Ga $4p$ orbitals to investigate the magnetic structure. We introduce Kondo coupling between electrons in Gd $\text{5}d$ orbitals and localized spins in Gd $\text{4}f$ orbitals and present the modified band structure when localized spins form a magnetic order characterized by three $\mathit{q}$ vectors that connect the valence and conduction bands. We discuss the origin of the spin order based on the Ruderman-Kittel-Kasuya-Yosida mechanism and suggest that Coulomb interactions acting on electrons near the Fermi level can contribute to the ordering of localized spins.

In the phenomenon known as electron drag, a phonon thermal flux is established in a conducting crystal by an electric field applied under isothermal conditions through directed transfer of quasimomentum from the electronic charge current to the phonon subsystem. Prior understanding of this phenomenon involves a thermal current composed of low-frequency acoustic phonons that is in the same direction as the charge current. This results in an increase of the Peltier thermopower. Here, we show that it is also possible to establish a phonon thermal current that is in the opposite direction to the charge current, which we refer to as a reverse phonon thermal flux. We demonstrate this behavior both through a simple qualitative model and through first-principles calculations performed for three materials: p-type $\theta$-TaN, n-type BAs, and n-type Si. The reverse phonon flux is shown to arise through intervalley electron-phonon scattering processes involving high-frequency acoustic phonons. Unlike n-BAs and n-Si, the combined features in the band structure and phonon dispersions of p-type $\theta$-TaN promote a particularly large reverse phonon thermal flux comparable in magnitude to the oppositely directed thermal flux from low-frequency phonons. This work highlights a previously unrecognized behavior in the coupled electron-phonon system and advances our understanding of the rich physics of transport in solids.

Proper analysis of electron collisions in two spatial dimensions leads to the conclusion that the odd harmonics of the electron distribution function decay much slower than the even ones. At the same time, the number of long-lived odd harmonics quickly shrinks with increasing temperature. Focusing on a channel geometry with boundary scattering, we show that such behavior of the odd decay rates leads to a characteristic behavior of the conductance that we dub anomalous Knudsen effect: It initially grows with temperature but then starts to decrease, forming a peak. Further increase of the temperature forces the conductance to grow again because of the Gurzhi effect, associated with the crossover from ballistic to hydrodynamic transport. The simultaneous observation of the Gurzhi dip preceded by the anomalous Knudsen peak constitutes a particular signature of the long-lived modes in 2D electron transport at low temperatures.

Quantum geometry provides an intrinsic framework for characterizing the geometric structure of quantum states. It highlights its relevance to various aspects of fundamental physics. However, its direct implications for magnetic phenomena remain largely unexplored. Here, we report the observation of electric-field-induced nonlinear magnetization in the nonmagnetic semimetal ${\mathrm{WTe}}_2$ by using a second-harmonic magneto-optical Kerr effect (SMOKE) spectroscopy. We observe a robust nonlinear SMOKE signal that scales quadratically with current and persists up to 200 K. Theoretical modeling and scaling analysis indicate that this nonlinear magnetization is dominated by the orbital contribution and is intrinsically linked to the quantum Christoffel symbol. Just as the Christoffel symbol is a fundamental quantity encoding spacetime geometry in Einstein's general relativity, our work establishes a direct link between quantum geometry and nonlinear magnetization, and provides a geometric perspective for designing future orbitronic devices.

Conventional spin pumping, driven by magnetization dynamics, is longitudinal since the pumped spin current flows normal to the interface between the ferromagnet and the conductor. We predict Hall-type/transverse and unidirectional spin pumping into conductors by near-field electromagnetic radiation emitted by, e.g., magnetization dynamics. The joint effect of the electric and magnetic fields results in a pure spin current flowing parallel to the interface, i.e., a Hall-type spin pumping, which is highly efficient due to the strong coupling to the electric field. Such a transverse spin current is unidirectional, with the spatial distribution controlled by the magnetization direction. Our finding reveals a robust approach for generating and manipulating spin currents in future low-dimensional spintronic and orbitronic devices.

We investigate the superconducting properties of the two-dimensional electron gas at the (111) ${\mathrm{LaAlO}}_3/{\mathrm{SrTiO}}_3$ interface. Using a multiorbital tight-binding model defined on a hexagonal lattice, we analyze the emergence of superconductivity driven by both interlayer (nearest-neighbor) and intralayer (next-nearest-neighbor) pairing interactions, with a particular focus on the symmetry of the superconducting gap. We demonstrate that, in both pairing scenarios, the superconducting gap transforms according to the $A_1$ irreducible representation of the $C_{6v}$ point group. Within the interlayer pairing scenario, the superconducting phase is characterized by a fully gapped quasiparticle excitation spectrum exhibiting extended $s$-wave symmetry, accompanied by an enhancement of the superconducting gap magnitude in the vicinity of the van Hove singularity. Conversely, the intralayer pairing channel produces a distinctive double-dome structure in the superconducting phase diagram, with the gap symmetry evolving from a fully gapped, extended $s$-wave at low carrier densities to a nodal extended $s$-wave state at higher electron concentrations. The qualitative agreement with experimentally observed nonmonotonic behavior of the critical temperature $T_c\left(V_g\right)$ suggests that intralayer next-nearest-neighbor pairing may play a dominant role in the superconductivity of the (111) LAO/STO interface.

We report thermal-expansion and heat-capacity studies on ${\mathrm{Li}}_2{\mathrm{FeSiO}}_4$ single crystals which enable us to investigate critical behavior in magnetically quasi-two-dimensional (2D) material. Pronounced $\lambda$-shaped anomalies at the magnetic ordering temperature $T_{\mathrm{N}}$ imply significant magnetoelastic coupling. Our analysis of both the thermal-expansion and the specific heat data implies the crossover from 2D Ising-like behavior for $|(T-T_{\mathrm{N}})/T_{\mathrm{N}}|>0.3$ to 3D Ising behavior below $\simeq 1.3\times T_{\mathrm{N}}$. The 2D-like behavior is further supported by density functional calculations which show minimal dispersion perpendicular to the crystallographic ac planes of the layered structure, thereby indicating the 2D nature of magnetism at higher temperatures. Our results extend the available model materials of quasi-2D magnetism to a high-spin $S=2$ system with tetrahedrally coordinated ${\mathrm{Fe}}^{2+}$ ions, thereby illustrating how magnetic order evolves in a 2D Ising-like system with orbital degrees of freedom.

Using state-of-the-art quantum chemistry, we present a microscopic mechanism for ultrafast laser-induced long-range spin transfer in carbon chains to which two magnetic atoms (Ni) are attached. Here, the Ni atoms function as spin carriers, while the carbons provide the delocalized conjugated $p_z$-character orbitals to bridge them. First, we establish that the key to the whole process is the virtual excitations between the localized Ni atomic orbitals, and the conjugated orbitals, through which the two Ni atoms can indirectly couple to each other. Second, the efficiency of dynamic interaction depends on the orbital phases of carbon atoms bonded to Ni, with longer-distance transfers benefiting from favorable degeneracies and phase alignments. Third, even when conjugated orbitals interact with only one Ni atom, their coherent superposition facilitates long-distance spin coupling. Fourth, the different structural characters between cis and trans configurations result in distinct spin-transfer behavior. Fifth, the spin-transfer speed and efficiency are tunable based on the position of magnetic centers. We name this set of interaction mechanisms dynamical Goodenough-Kanamori-Anderson (GKA) rules, because it resembles the well-known static GKA rules, in which the nature of the indirect metal-to-metal coupling (i.e., ferromagnetic versus antiferromagnetic) is dictated by the occupancy of the degenerate $p_z$ orbitals of the bridging oxygen. Unlike in the static case, the spin density here is dynamically transferred between two Ni atoms via well-designed laser pulses.

In collinear antiferromagnetic insulators, the Dzyaloshinskii-Moriya interaction and dipolar interaction can induce spin-orbit fields and influence magnon spin transport behavior. Beyond these mechanisms, we propose that the symmetric $\widehat{\mathrm{\Gamma }}$ interaction can also couple the spin-degenerate magnon modes as an effective spin-orbit field. To investigate the effect of $\widehat{\mathrm{\Gamma }}$ interaction on spin relaxation, we construct the magnon kinetic equations by self-consistently incorporating all relevant magnon-magnon scattering processes arising from both the isotropic exchange $J$ interaction and the symmetric $\widehat{\mathrm{\Gamma }}$ interaction. Numerical solutions reveal that the momentum-dependent effective spin-orbit field induced by the $\widehat{\mathrm{\Gamma }}$ interaction leads to inhomogeneous broadening and results in D'yakonov-Perel' type spin relaxation. Moreover, emergent scattering channels generated by the $\widehat{\mathrm{\Gamma }}$ interaction partially exhibit the Elliott-Yafet characteristics, which become more pronounced in strongly anisotropic crystals. Our results provide theoretical support for magnon spin dynamics in antiferromagnetic insulators and offer potential guidance for the design of spintronic devices.

We present an analytical study of the ground-state phase diagram for dilute two-dimensional spin-$\frac{1}{2}$ Fermi gases exhibiting $d$-wave altermagnetic spin splitting under $s$-wave pairing. Within the Bogoliubov–de Gennes mean-field framework, four distinct phases are identified: a Bardeen-Schrieffer-Cooper type superfluid, a normal metallic phase, a nodal superfluid with topological Bogoliubov Fermi surfaces (TBFSs), and Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states with finite center-of-mass momentum. Among these, the FFLO states and TBFSs exemplify two unconventional forms of superconductivity. Considering the simplicity of this model, with only one band, zero net magnetization, and $s$-wave paring, the emergence of both unconventional phases underscores the pivotal role of altermagnetic spin splitting in enabling exotic pairing phenomena. This analytical study not only offers a valuable benchmark for future numerical simulations, but also provides a concrete experimental roadmap for realizing FFLO states and TBFSs in altermagnets.

The Josephson diode effect, where the switching current magnitude depends on its direction, arises when both time-reversal and inversion symmetries are broken, often achieved by a combination of spin-orbit interaction and applied magnetic fields. Taking advantage of the strong spin-orbit coupling inherent in three-dimensional topological insulators, we study this phenomenon in $\mathrm{Nb}/{\mathrm{Bi}}_{0.8}{\mathrm{Sb}}_{1.2}{\mathrm{Te}}_3/\mathrm{Nb}$ Josephson weak-link junctions. Under an in-plane magnetic field perpendicular to the current direction, we observe a pronounced Josephson diode effect with efficiencies up to 7%. A crucial component of this behavior is the nonsinusoidal current-phase relationship and an anomalous phase shift, which we attribute to the presence of a ballistic supercurrent component due to the surface states. These findings open up new avenues for harnessing and controlling the Josephson diode effect in topological material systems.

We investigate the spin properties of charge carriers in vertically coupled InAs/InAlGaAs quantum dots grown by molecular beam epitaxy, emitting at telecom C-band wavelengths, with a silicon $\delta$-doped layer. Using time-resolved pump-probe Faraday ellipticity measurements, we systematically study single-, two-, and four-layer quantum dot (QD) configurations to quantify how vertical coupling affects key spin-coherence parameters. Our measurements reveal distinct layer-dependent effects: (i) Adding a second QD layer flips the resident charge from electrons to holes, consistent with optically induced electron tunneling into lower-energy dots and resultant hole charging. (ii) Starting from the four-layer sample, the pump-probe signal develops an additional nonoscillating, decaying component absent in single- and two-layer samples, attributed to multiple layer growth changing the strain environment, which reduces heavy-hole and light-hole mixing. (iii) With four layers or more, hole spin mode locking (SML) can be observed, enabling quantitative extraction of the hole coherence time $T_2\approx 13$ ns from SML amplitude saturation. We also extract longitudinal spin relaxation ($T_1$) and transverse ($T_2^{*}$) spin dephasing times, g-factors, and inhomogeneous dephasing parameters for both electrons and holes across all layer configurations. The hole spin dephasing times $T_2^{*}$ remain relatively constant (2.3–2.7 ns) across layer counts, while longitudinal relaxation times $T_1$ decrease with increasing layers (from $0.9\mu \mathrm{s}$ for single-layer to $0.32\mu \mathrm{s}$ for four-layer samples). These findings provide potential design guidelines for engineering spin coherence in telecom-band QDs for quantum information applications.

The growing interest in topological materials with symmetry-protected surface states as catalytic platforms has sparked the emerging field of topocatalysis. As robust transport is one of the key features of topological insulators, here we explore current-induced molecular dissociation in a transport setup. Using the non-equilibrium Green's function formalism, we compare how the occupancies of bonding and antibonding levels, as well as the associated electronic forces in a diatomic molecule, are affected when the molecule is coupled to either a metallic (graphene) or a topological (Kane-Mele) substrate. We find a greater dissociative capability in the topological substrate than in graphene, a difference mainly attributed to the localized nature of the edge states. The inclusion of vacancy disorder within the substrate further enhances this disparity in the dissociative force. Our findings highlight the role of topological protection in molecular dissociation under non-equilibrium conditions, pointing to opportunities for robust catalysis in topological materials.

Magic-angle twisted bilayer graphene displays a complex phase diagram as a function of flat-band filling, featuring compressibility cascade transitions and a variety of competing ground states with broken spin, valley, and point-group symmetries. Recent terahertz photocurrent spectroscopy experiments have shown a dependence on the filling, which is not consistent with the simplest cascade picture of sequential filling of equivalent flat bands. In this work, we show that when time-reversal symmetry is broken due to valley polarization, a magnetic injection photocurrent develops, which can be used to distinguish different spin-valley polarization scenarios. Using the topological heavy fermion model, we compute both shift and injection currents as a function of filling. We argue that current experiments can be used to determine the spontaneous valley polarization.

Quantum phase transitions are among the most intriguing phenomena that can occur when the electronic ground state of correlated metals are tuned by external parameters such as pressure, magnetic field, or chemical substitution. Such transitions between distinct states of matter are driven by quantum fluctuations, and can give rise to macroscopically coherent phases that are at the forefront of condensed matter research. However, the nature of the critical fluctuations, and thus the fundamental physics controlling many quantum phase transitions, remain poorly understood in numerous strongly correlated metals. Here we study the model material ${\mathrm{CeCu}}_{5.8}{\mathrm{Ag}}_{0.2}$ to gain insight into the implications of critical fluctuations originating from different regions in reciprocal space. By employing an external magnetic field along the crystallographic $a$ and $c$ axis as auxiliary tuning parameter, we observe a pronounced anisotropy in the suppression of the quantum critical fluctuations, reflecting the spin anisotropy of the long-range ordered ground state at larger silver concentration. Coupled with the temperature dependence of the quantum fluctuations, these results suggest that the quantum phase transition in ${\mathrm{CeCu}}_{5.8}{\mathrm{Ag}}_{0.2}$ is driven by three-dimensional spin-density wave fluctuations.

We investigate $26–110\mathrm{nm}$-thick tensile strained HgTe films, which possess surface-state transport characteristic of three-dimensional topological insulators. The high transport mobility and low intrinsic doping of the material permits investigating the Landau level spectrum around the charge neutrality point to low magnetic fields and with small electric fields from the top gate electrode. The experimental findings are in quantitative agreement with eight-orbital $\mathbf{k}·\mathbf{p}$ band structure theory. We quantify the parameter regimes where transport can be attributed solely to topological surface states and those where bulk states from quantum confinement have to be taken into account, as a function of layer thickness and carrier density.

Hilbert space fragmentation induced by dynamical constraints has emerged as a novel mechanism underlying nonergodic behavior in quantum many-body systems. Focusing on this phenomenon, we report a parameter-dependent Hilbert space fragmentation of the one-dimensional Rydberg atom array in the antiblockade regime. We explicitly identify and classify a set of distinct nonequilibrium dynamical phases in the parameter space and analyze their dynamical characteristics. We point out that their quasiperiodic behavior is jointly governed by multipath excitation interference and multiphoton cascaded excitation structures, further revealing fundamental differences in the state connectivity structure and effective dimensionality of the corresponding subspaces. By constructing a complete fragmented quantum phase diagram, we clearly delineate the transition of the Hilbert space from global thermalization to fragmented behavior. Furthermore, we demonstrate the process of secondary fragmentation that enables additional control over the accessible subspaces through local constraints. This work demonstrates the potential of realizing highly programmable nonthermal dynamics through antiblockade mechanisms, providing a theoretical foundation for the exploration and control of exotic nonequilibrium quantum phases in many-body systems.