The appearance of angular momentum in the nuclear motion of molecular systems lacking inversion symmetry under imposed thermal gradients presents a novel mechanism with potential implications for spintronics, magnetic response, and energy transport in such systems. Here, we explore this phenomenon, using theoretical analysis and numerical simulations to study angular momentum generation in several driven chiral molecular models. We demonstrate that significant vibrational angular momentum can be induced under both mechanical and thermal driving, with magnitude comparable to those values calculated for optically driven chiral phonons. We find that generation of angular momentum is a common and general phenomenon in driven chiral structures, highlighting the role of symmetry breaking in the (nonequilibrium) internal atomic motion of such systems.

We report on the exchange coupling phenomena emerging at low temperatures in amorphous TbFe-based bilayers with perpendicular magnetic anisotropy. The ferrimagnetic layers have different compositions: one layer is dominated by the magnetic moment of Fe, the other by the magnetic moment of Tb. The antiferromagnetic exchange coupling between the two layers, along with the formation of an intermixing layer at the interface, leads to the emergence of (double) exchange bias [(D)EB] at low temperatures after field cooling. The composition of the Fe-dominated layer and the stacking order of layers are shown to have a significant impact on this behavior, while changes in the Tb-dominated layer and tailoring of the interlayer region influences it to a lesser degree. The most stable DEB was obtained in a ${\mathrm{Tb}}_{36}{\mathrm{Fe}}_{64}/{\mathrm{Tb}}_{19}{\mathrm{Fe}}_{81}$ bilayer structure, with clearly separated, oppositely biased subloops at temperatures up to 120 K. Further, a substantial overcrossing of hysteresis branches between 80 and 140 K was observed for some samples. This is shown to be connected to ultraslow magnetization dynamics similar to magnetic viscosity, which are greatly influenced by the applied magnetic field and temperature. Relaxation times ranging from tens of seconds to several hours are observed. By comparing minor loops with and without relaxation, a simple qualitative model is derived to explain the observed behavior of magnetization relaxation.

Using pump-probe Faraday and Kerr rotation measurements, we investigate the ultrafast magnetization dynamics induced by femtosecond laser pulses in a BiYIG/Co-based heterostructure epitaxially grown on GGG(001) substrate. The Kerr measurements reveal the excitation of high-frequency exchange standing spin-wave modes, whereas the Faraday measurements detect only the ferromagnetic resonance mode. Moreover, the Kerr response exhibits faster remagnetization following the demagnetization dynamics. These differences are explained by considering the average magnetization profile of the magneto-optical (MO) Faraday effect and the unequal depth sensitivity of the MO Kerr effect. They also allow deeper insight into the mechanisms driving the magnetization dynamics. Furthermore, we identify in the Kerr signal a contribution induced by the strain pulse in the BiYIG layer and gadolinium gallium garnet (GGG) substrate, which is absent in the Faraday response and should not be misinterpreted as a magnetic effect. These findings establish important connections with existing literature on laser-induced ultrafast magnetization dynamics in magnetic garnets and advance the fundamental understanding of these dynamics.

Recently, proposals for realizing a nonreciprocal superradiant quantum phase transition (SQPT) have been put forward, based on either nonreciprocal interactions between two spin ensembles or the Sagnac-Fizeau shift in a spinning cavity. However, experimental implementation of such a nonreciprocal SQPT remains challenging. This motivates the search for new mechanisms capable of producing a nonreciprocal SQPT. Here, we propose an alternative approach to realize a nonreciprocal SQPT, induced by the magnon Kerr effect (MKE), in a cavity magnonic system, where magnons in a yttrium iron garnet (YIG) sphere are coupled to cavity photons. The MKE coefficient is positive ($K>0$) when the bias magnetic field is aligned along the crystallographic axis [100], but negative ($K<0$) when aligned along the axis [110]. We show that the steady-state phase diagram for $K>0$ differs markedly from that for $K<0$. This contrast is the origin of the nonreciprocal SQPT. By further studying the steady-state magnon occupation and its fluctuations versus the parametric drive strength, we demonstrate that the SQPT becomes nonreciprocal, characterized by distinct critical thresholds for $K>0$ and $K<0$. Moreover, we introduce a bidirectional contrast ratio to quantify this nonreciprocal behavior. Our work provides a mechanism for realizing the nonreciprocal SQPT, with potential applications in designing nonreciprocal quantum devices.

Spin precession experiments in lateral spin devices are a powerful tool for probing the spin transport properties of materials. These experiments can be quantitatively described using the Bloch diffusion equation, which offers a practical framework for modeling spin-related phenomena. In this work, we present calculations of the spin density across heterogeneous, diffusive spintronic devices. The modeled devices feature spin transport channels that include both isotropic and in-plane anisotropic spin relaxation regions. We analyze how different geometric configurations and spin transport parameters influence the lineshape of spin precession signals under magnetic fields applied in different orientations and compare the results with experimental observations. Our results introduce a theoretical framework for interpreting spin transport measurements in lateral graphene spin devices. The framework is especially relevant when the graphene is partially proximitized by other two-dimensional materials, where proximity-induced spin-orbit coupling leads to anisotropic spin relaxation.

Multilayer graphene materials have recently emerged as a fascinating versatile platform for correlated electron phenomena, hosting superconductivity, fractional quantum Hall states, and correlated insulating phases. A particularly striking experimental observation is the recurring correlation between nematicity in the normal state—manifested by spontaneous breaking of the underlying $C_3$ symmetry—and the stabilization of robust superconducting phases. Despite its ubiquity across different materials, devices and experiments, this trend has thus far lacked a clear microscopic explanation. In this work, we identify a concrete mechanism linking nematic order to enhanced superconductivity. We demonstrate that $C_3$-symmetry breaking strongly reshapes the Bloch wave functions near the Fermi level, producing a pronounced enhancement and redistribution of the so-called quantum metric. This effect drastically amplifies superconducting pairing mediated by the quantum geometric Kohn-Luttinger mechanism [G. Shavit et al., Phys. Rev. Lett. 134, 176001 (2025)]. Our analysis reveals that nematicity naturally boosts the superconducting coupling constant in experimentally relevant density regimes, providing a compelling explanation for observed correlations. These results establish the central role of geometric effects in graphene superconductivity and highlight nematicity as a promising avenue for engineering stronger unconventional superconducting states.

We report a ferromagnetic-like anomalous Hall resistivity and giant isotropic negative magnetoresistance (NMR) in the antiferromagnetic half-Heusler compound DyPdBi. The FM-like anomalous Hall resistivity appears exclusively in antiferromagnetic state II, yet it is not coupled to magnetization, indicating a Berry-curvature origin. Additionally, the magnetoresistance drops by 98%, and the NMR persists above the Néel temperature ($T_{\mathrm{N}}$). We attribute both phenomena to a half-topological-semimetal (HTS) state, similar to that proposed for TbPdBi, arising from weak band inversion strength (BIS). This state enhances spin polarization, reducing Berry curvature cancellation and strengthening anomalous Hall effect (AHE). These observations suggest that weak BIS in the RPdBi family gives rise to an HTS that potentially interacts with exotic spin states, producing an exceptionally large AHE. This study highlights a strategy for engineering large AHE in half-Heusler antiferromagnets, and advances the further topological spintronics design.

Anisotropic skyrmion Hall effect (A-SkHE) in two-dimensional (2D) magnetic systems represents a captivating phenomenon in condensed-matter physics and materials science. While conventional antiferromagnetic systems inherently suppress this effect through parity-time symmetry-mediated cancellation of Magnus forces acting on skyrmions, A-SkHE is primarily confined to ferromagnetic platforms. Here, we present a paradigm-shifting demonstration of this phenomenon in spin-splitting 2D antiferromagnets through the investigation of altermagnetic skyrmions. Combining comprehensive symmetry analysis with theoretical modeling, we elucidate the mechanism governing A-SkHE realization in 2D altermagnetic systems and establish a quantitative relationship between the transverse velocity of altermagnetic skyrmions and applied current orientation. Using first-principles calculations and micromagnetic simulations, this mechanism is further illustrated in a prototypical altermagnetic monolayer ${\mathrm{V}}_2\mathrm{SeTeO}$. Crucially, we identify that the $\left[C_2\parallel C_{4z}\mathbf{t}\right]$ symmetry-protected anisotropic field serves as the critical stabilizer for maintaining the A-SkHE in this system. Our results greatly enrich the research on 2D altermagnetism and skyrmions.

This paper presents a theoretical investigation of electron-magnon scattering processes in the ultrafast demagnetization in itinerant ferromagnets. In the framework of a ferromagnetic model system, we compute the spin-dependent dynamics of electrons in itinerant Bloch states by including electron-magnon and electron-electron scattering processes on an equal footing. While the former process flips the electronic spin accompanied by the creation or destruction of a magnon, the latter exchanges electronic angular momentum with the lattice due to the influence of spin-orbit coupling. We show that, for a realistic choice of the electron-magnon interaction and deposited pulse energy, the interplay of these two different scattering mechanisms leads to the creation of magnons and a transfer of angular momentum to the lattice that constitutes an essentially nonequilibrium microscopic scenario for the ultrafast demagnetization process in itinerant ferromagnets.

Can strong repulsive interactions be shown to give rise to pairing in a controlled way? We find that for a single flavor-polarized band, there is a small expansion parameter in the low density limit, once the Bloch wave-function form factor is taken into account. A perturbative expansion is possible, even if the interaction is much stronger than the Fermi energy ${\epsilon }_F$. As a matter of principle, our work shows analytically how strong pairing can emerge from strong repulsion. We illustrate our method with two examples: a two-dimensional Dirac model and a one-dimensional tight-binding model with two orbitals. In the latter case, using density matrix renormalization group, we show that the analytical theory indeed guided us to discover the parameter regime where $p$-wave pairing with order-1 strength is dominant.

We report the emergence of Majorana flat bands (MFBs) in the vortex line of superconducting (SC) time-reversal symmetry-breaking Weyl semimetals. By considering a Weyl semimetal as a stack of Chern insulators with varying Chern numbers along one ($z$) direction, we decompose the vortex bound states of SC Weyl semimetals into those of $k_z$-resolved SC Chern insulators. Through analytical and numerical calculations of the topological phase diagram of the SC Chern insulators, we explain the appearance of MFBs and determine the exact boundaries of them. Notably, the tuning of chemical potential or pairing strength results in the MFBs along the entire $k_z$ axis. We find that the MFBs are absent in SC type-$\mathrm{II}$ Weyl semimetals due to the inversion symmetry-breaking term. To characterize the MFBs, we propose a $k_z$-resolved $Z_2$ Chern-Simons invariant as the topological indicator. Finally, we take an attractive Hubbard interaction into consideration, and the aforementioned SC Weyl semimetal with BCS pairing can be realized under appropriate parameters.

Classical and quantum Markov networks—including Gibbs states of commuting local Hamiltonians—are characterized by the vanishing of conditional mutual information (CMI) between spatially separated subsystems. Adding local dissipation to a Markov network turns it into a hidden Markov network, in which CMI is not guaranteed to vanish even at long distances. Nevertheless, it is unclear whether the Markov property still holds approximately after dissipation, i.e., whether CMI decays with distance. In this work, we show that high-temperature hidden Markov networks are approximately Markovian under a wide class of local perturbations. We establish that CMI in high-temperature Gibbs states subject to local dissipation decays exponentially: (i) for classical Hamiltonians subject to arbitrary local transition matrices and (ii) for commuting local Hamiltonians subject to unital channels that obey certain mild restrictions. Our result provides the first rigorous understanding of long-range CMI in a broad class of models, offering a new lens to analyze quantum states through their information structure. It also leads to new results in understanding teleportation, mixed-state phases of matter, state preparation, and compressibility of quantum states.

We investigate low-energy excitons in rhombohedral pentalayer graphene encapsulated by hexagonal boron nitride (hBN/R5G/hBN), focusing on the regime at the experimental twist angle $\theta =0.{77}^{\circ }$ and with an applied electric field. We introduce a new low-energy two-band model of rhombohedral graphene that captures the band structure more accurately than previous models while keeping the number of parameters low. Using this model, we show that the centres of the exciton Wannier functions are displaced from the moiré unit cell origin by a quantized amount—they are instead localized at $C_3$-symmetric points on the boundary. We also find that the exciton shift is electrically tunable: by varying the electric field strength, the exciton Wannier center can be exchanged between inequivalent corners of the moiré unit cell. Our results suggest the possibility of detecting excitonic corner or edge modes, as well as novel excitonic crystal defect responses in hBN/R5G/hBN. Lastly, we find that the excitons in hBN/R5G/hBN inherit excitonic Berry curvature from the underlying electronic bands, enriching their semiclassical transport properties. Our results position rhombohedral graphene as a compelling tunable platform for probing exciton topology in moiré materials.

While type-II silicon clathrates have shown promising room-temperature photoluminescence, their intrinsic optical properties remain unclear due to the presence of surface oxides, inhomogeneous and significant residual sodium concentrations, and contributions from disordered phases. These factors have hindered reliable identification of the emission band and limited development of the clathrates as light-emitting materials. In this work, we present a systematic photoluminescence (PL) study of deuterium-passivated, low-Na-doped, Si clathrate films, in which Na-related donor states and native defect levels are significantly reduced. A previously unrecognized emission feature associated with a surface oxide layer is identified and chemically removed, revealing a sharper emission spectrum composed of two dominant emission bands. We associate the higher energy band with the emission from the clathrate framework and the lower one with hydrogenated disordered or amorphous Si present as an impurity phase in the material. Temperature- and excitation-dependent PL measurements place the optical band gap of the clathrate phase near 1.9 eV, consistent with theoretical predictions. These results resolve long-standing ambiguities in Si clathrate PL emission and demonstrate a practical route to accessing near-intrinsic optical transitions. This lays the groundwork for engineering clathrate-based optoelectronic materials and highlights their potential as silicon-compatible light emitters.

Photovoltaic Hall effect, i.e., generation of a photocurrent perpendicular to the bias electric field, is an interesting platform of Berry curvature engineering by external fields. Floquet engineering aims at generation of light-induced Berry curvature associated with topological phase transition in solids, which may manifest itself as a light-induced anomalous Hall effect. However, recent studies have pointed out a larger contribution by momentum asymmetry of photocarriers, termed a field-induced circular photogalvanic effect. Except for numerical studies, the two mechanisms have been described by different theoretical frameworks, hindering a coherent understanding. Here, we develop a unified theory of the photovoltaic Hall effect capable of describing both mechanisms on an equal footing. We reveal that the bias electric field alters the interband transition dipole moment and transition energy, both contributing to the field-induced circular photogalvanic effect in nonmagnetic materials. These effects are governed by an electric field-induced Berry curvature and the shift vector coupled to bias field, respectively. A resonant enhancement of the transverse photocurrent is found in GaAs owing to the topological character of the valence band. We also clearly distinguish the anomalous Hall effect by light-dressed states within the density matrix calculation using the length gauge. Our theory unifies a number of nonlinear optical processes in a physically transparent way and presents a geometric picture of the third-order nonlinear response under light and bias fields, shedding new light on Berry curvature engineering.

Monolayer 1$T{}^{\prime }-{\mathrm{MoS}}_2$ exhibits spin- and valley-dependent massive tilted Dirac cones with two velocity correction terms in low-energy effective Hamiltonian. We theoretically investigate the longitudinal diffusive magneto-conductivity of monolayer 1$T{}^{\prime }-{\mathrm{MoS}}_2$ by using the linear response theory. It is shown that the Weiss oscillations are polarized in spin and valley degrees of freedom, under uniform electric fields and a weak one-dimensional spatially periodic electrostatic potential modulation. The spin polarization, the valley polarization and the spin-valley polarization can be switched by flipping the external electric fields. The polarization is found not only in the amplitudes but also in the periods of the Weiss oscillations. It is found that the period polarization in Weiss oscillations originates from the polarized effective Fermi energies or the polarized Landau level spacing scales. In Weiss oscillations, polarization in amplitude does not imply the presence of polarization in period, whereas polarization in period is accompanied by polarization in amplitude. The superposition of polarization in amplitude and polarization in period enables the appearance of considerable polarization in Weiss oscillations under relatively weak external electric fields.

Deciphering the atomistic mechanism governing humidity-dependent interfacial friction remains a fundamental challenge across physics, chemistry, medicine, and materials science. Here, we employ first-principles calculations to systematically investigate the frictional behaviors of bilayer graphene (BLG) with varying interfacial water (${\text{H}}_2\text{O}$) coverage, with a particular focus on the contrasting responses of commensurate and incommensurate contacts. Our findings reveal a striking dichotomy: As ${\text{H}}_2\text{O}$ coverage increases to approximately 0.4 monolayer, commensurate BLG interfaces experience a dramatic reduction in friction, reaching a minimum, whereas incommensurate contacts exhibit a moderate increase in friction, peaking near 0.6 monolayer. Beyond these critical humidity cites, friction in commensurate systems gradually increases toward a saturation regime, while incommensurate systems display a declining trend before plateauing. To validate these distinct behaviors, we establish a generalized registry index framework that extends the conventional registry index [N. Marom $et al$., Phys. Rev. Lett. 105, 046801 (2010)] by explicitly incorporating (i) interlayer-distance-dependent vdW interactions modulated by water intercalation, (ii) humidity-induced commensurate-incommensurate phase transitions, and (iii) molecular pinning sites imparted by confined ${\text{H}}_2\text{O}$ molecules within the BLG heterostructure. Collectively, this work not only reveals the atomistic mechanism of humidity as an effective tuning parameter for frictional control in two-dimensional materials but also provides a robust descriptor with predictive power for the rational design of adaptive, environment-responsive nanolubrication systems.