Abstract 4H b -TaS 2 is a natural heterostructure of correlated (T) and superconducting (H) layers. Using time- and angle-resolved photoemission spectroscopy, we observe a narrow feature slightly above the Fermi level on the T-layer termination, corresponding to the band edge of a charge-density-wave (CDW)-gapped electron-like dispersion. Above a characteristic incident fluence, the fitted CDW gap becomes indistinguishable from zero, while enhanced occupied-state spectral weight persists for tens of picoseconds after hot carriers decay. Together, these spectral and dynamical signatures identify a transient metastable electronic state. Its much shorter lifetime than that of the persistent hidden state in bulk 1T-TaS 2 is consistent with a role for interrupted direct T–T stacking, although relaxation channels involving the H layers may also contribute. These results highlight the influence of the interlayer environment on nonequilibrium-state stability and establish 4H b -TaS 2 as a platform for ultrafast control of correlated states.
Abstract We investigate the quantized charge pumping in graphene with Rashba spin–orbit coupling (RSOC) under two time-periodic staggered potentials. Surprisingly, the quantized charge pumped per cycle exhibits a sharp dependence on the transverse boundary conditions: a zero quantized charge is obtained under periodic boundary conditions (consistent with bulk thermodynamic limits), whereas a quantized value of 1 per spin emerges under open boundary conditions. This topological transition induced by the transverse boundary conditions persists even for large system widths, revealing a discontinuous crossover from finite to infinite geometries without relying on topological edge states at the boundaries. We attribute this phenomenon to RSOC-induced intravalley reflection at transverse boundaries, which modifies the winding number of the pumping cycle. These results challenge conventional wisdom about finite-to-infinite transitions in condensed matter systems and advance the fundamental understanding of boundary-sensitive quantum transport in multivalley systems.
Abstract We present a refined strong-field approximation (SFA) theory incorporating the intermediate-state Coulomb interaction for nonsequential double ionization (NSDI). By introducing the Coulomb−Volkov wave function into the intense-field many-body S-matrix theory, we develop an intermediate-state Coulomb-corrected strong-field approximation (ICSFA) to address the long-standing deficiency of neglecting the Coulomb potential acting on the recolliding electron. Using the recollision excitation with subsequent ionization (RESI) mechanism in helium as a benchmark, we perform a systematic comparison between the conventional SFA and the ICSFA. The correlated electron momentum distributions (CEMDs) calculated via ICSFA show a significant redistribution of electron yield toward high-momentum regions and off-axis quadrants, which aligns quantitatively with experimental observations, whereas the SFA fails to reproduce these features. Concurrently, the joint energy distributions (JEDs) manifest a corresponding evolution. Analysis reveals that the Coulomb potential promotes large-angle scattering, thereby reshaping the CEMD and the JED. Furthermore, the ICSFA reveals a substantial enhancement of multiple-return recollision (MRR) trajectories, stemming from the combined effects of Coulomb focusing (manifested through the normalization factor) and the energy-dependent enhancement of the inelastic scattering cross-section. Our work establishes that the intermediate-state Coulomb interaction is indispensable for a quantitatively accurate description of strong-field correlated electron dynamics.
Abstract Terahertz (THz) pump–THz probe spectroscopy has emerged as a powerful platform for investigating ultrafast nonlinear light–matter interactions. However, the physical origin of recently reported THz signal enhancement remains controversial because contributions from THz generation and electro–optic detection are often coupled. Here, we use a Fe 4 GeTe 2 spintronic THz emitter together with a ZnTe electro–optic detector to demonstrate that, with fixed THz pump polarity, reversing the magnetic-field direction of the Fe 4 GeTe 2 emitter does not change the signal enhancement or induce suppression, indicating that the modulation originates from the nonlinear electro–optic response of the ZnTe detector rather than the THz emitter. Furthermore, controlling the polarity of the THz pump field reveals a pronounced asymmetric response: a positive THz field induces signal enhancement, whereas a negative field leads to suppression, revealing strong polarity-dependent THz pump–THz probe modulation. This behavior cannot be solely attributed to carrier redistribution in the conduction band and is consistently described by a model incorporating both linear Pockels and nonlinear Kerr effects in ZnTe. This polarity-dependent reversal of the linear Pockels contribution accounts for the observed polarity-dependent THz-field-induced absorption modulation. These results clarify the physical origin of THz pump–THz probe modulation, establish detection-induced nonlinearity as the dominant mechanism governing the measured response, and highlight the importance of treating electro–optic detection as an active nonlinear element in THz pump–THz probe spectroscopy.
Abstract Rydberg atom-based time receiving systems enable high-sensitivity demodulation of long-wave signals for precise one-pulse-per-second (1PPS) output, surpassing limitations of conventional electronic long-wave receivers. Here, we first report the theoretical and experimental demonstration of a nanosecond-jitter Rydberg time receiving system for eLoran signals. We establish a novel theoretical model that quantitatively reveals the relationship between timing jitter and system parameters exemplified by DC Stark shift and coupling-beam Rabi frequency. Experimentally, we first demonstrate timing 1PPS output based on atomic system, achieving a root-mean-square (RMS) timing jitter of 27.90 ± 0.39 ns. Furthermore, we demonstrate timing performance of our system across high noise levels or low input signal amplitudes, validating the robustness under practical weak eLoran signal. This work validates the feasibility of Rydberg atom-based architectures for high-precision ground-based timing and establishes a performance benchmark for next-generation atomic-optical positioning, navigation, and timing (PNT) systems.
Abstract Recent experiments support that the magic-angle graphene family can be modeled by a periodic array of correlated quantum impurities immersed in a Dirac sea. This work analytically demonstrates that, with (anti-) Hund’s interactions that can originate from electron-phonon couplings, a single impurity can exhibit novel quantum phase transitions, and readily nurture the pairing potential and pseudogap phenomenon relevant to this moiré family. For broad applicability, we tackle a spin-valley Anderson impurity with general symmetry-allowed (anti-) Hund’s parameters ( J D , J S ), and derive its full phase diagram at half-filling. While the model reduces to well-known Kondo problems in certain limits, we uncover that in the large J D regime, the low-energy physics is controlled by a novel “pair-Kondo” coupling between the bath and an impurity valley-doublet. Using bosonization–refermionization mapping, we show there is a BKT transition from a Fermi liquid with pairKondo resonance, into an anisotropic doublet phase that exhibits a non-analytic zero-energy kink in the impurity spectral function, and non-universal power-law scaling in impurity susceptibilities. Importantly, by analyzing the pairing potentials across the phase diagram, we unveil ubiquitous existence of attractive channels under general (anti-) Hund’s interactions. More crucially, we analytically reveal the pseudogap shoulders represent multiplet excitations induced by the injected electron or hole, and derive ansätze of correlation self-energy that reproduce the pseudogap phenomenon in the lattice. All results are established analytically, with further verification by numerical renormalization group calculations.
Abstract Multiaxial magnetic states offer a route beyond binary spintronic functionalities and enable zero-magnetic-field spin orbit torque (SOT) switching via mirror symmetry breaking, yet remain unexplored. Here, we uncover field-free multistate SOT switching in a SrIrO 3 /SrRuO 3 bilayer with exceptionally large monoclinic distortion. Pulsed current excitations fully map all twelve deterministic transitions among the four states, through a systematic switching protocol defined by two characteristic current densities. In-situ scanning nitrogen-vacancy (NV) center magnetometry provides direct real-space evidence for previously unobserved in-plane canted states, and spin dynamics simulations uncover a two-step switching pathway, driven by the concerted action of spin torques and the effective anisotropy field within the fourfold anisotropy landscape. Our results demonstrate that precise lattice-symmetry engineering enables the creation and control of multiaxial magnetic states for field-free multistate spintronic devices.
Abstract Multiferroic materials offer a promising platform for ultrafast optical control of coupled magnetic and polar orders. However, a prerequisite for such control is to precisely identify how the magnetically induced polarization manifests itself on the ultrafast timescale, and then to probe its dynamics upon external perturbations. Here, we address this issue in the polar magnet Fe 2 Mo 3 O 8 by combining static and time-resolved second harmonic generation (SHG). Temperature-dependent static SHG reveals that, among the symmetry-allowed tensor elements, only χ ccc (2) exhibits a pronounced anomaly at the antiferromagnetic transition ( T N ≈ 60 K), identifying χ ccc (2) as the nonlinear susceptibility tensor element coupled to the magnetically induced polarization. Guided by this result, time-resolved SHG selectively tracks the dynamics of this tensor element following ultrafast photoexcitation. We observe a rapid enhancement of the χ ccc (2) -related SHG signal, followed by biexponential recovery. The response is independent of the pump polarization and reaches saturation at a remarkably low fluence, indicating a highly efficient coupling between optical excitation and the magnetically induced polarization. These results establish SHG as tensor-selective probe of ultrafast magnetoelectric dynamics and demonstrate the high sensitivity of the magnetically induced polarization in Fe 2 Mo 3 O 8 to optical excitation.
Abstract The reliability of simulations of thermal properties in micro-/nano-scale structures critically depends on the accuracy of potential function. While empirical force fields offer limited precision, machine learning potentials effectively bridge this gap by combining the computational accuracy of density functional theory with the efficiency of empirical force fields. This review provides a systematic investigation of various frameworks of machine learning potentials, including descriptors, training methodologies, and accuracy. Furthermore, a comparison of their predictive performance for thermal conductivity across different material systems is presented. Finally, key challenges and future research directions for machine learning potentials are discussed, aiming to promote their applications in thermal transport studies and enhance the understanding of heat conduction mechanisms.
Abstract Topological materials, ranging from topological insulators to semimetals, host many novel quantum phenomena, including the quantum spin Hall effect and topological Fermi arcs. Transitions between these topological phases have attracted considerable research interest. We performed angle-resolved photoemission spectroscopy on WTe 2 , from monolayer to bulk, and revealed the evolution of the electronic structure and the band gap. Notably, the gap observed in the monolayer system is suppressed in the three layers, where the film becomes metallic. Variations in the topological properties with thickness are demonstrated by first-principles calculations. The topological Z 2 invariant is shown to oscillate between 1 and 0 upon addition of layers, originating from interlayer coupling-induced changes in band crossing. The system evolves into a Weyl semimetal when the conduction and valence bands touch near the Fermi level, and its topological nature is characterized by the Chern number. Our findings demonstrate the nonmonotonic dependence of topological states on dimensionality and how layer-driven electronic band reconfiguration leads to phase transitions in solids.
Abstract The exploration of high- T c superconducting hydrides at ambient pressure is significant for the field of physics and materials science. Herein, by employing hydrogen-storage alloys as the template, we incorporate quasi-molecular H 2 units into binary Laves phase alloy F d 3 ¯ m - A 2 X , thereby achieving robust electron–phonon coupling (EPC) at significantly reduced pressures. Through high-throughput screening of F d 3 ¯ m - A 2 X H 16 ( A = group IIA elements, X = group IIIB elements), we identify eight dynamically stable compounds within 150 GPa. Among these candidates, Mg 2 AcH 16 is dynamically stable at 20 GPa, and Ca 2 AcH 16 maintains dynamic stability at ambient pressure. Our calculations demonstrate that charge transfer occurs from A and X atoms to the antibonding orbitals of elongated H 2 units (with H-H bond lengths from 0.85 to 0.96 Å), which concurrently activates mid-frequency H-dominated phonon modes that dominate EPC strength. Notably, Mg 2 AcH 16 exhibits a superconducting transition temperature of 221 K at 70 GPa ( λ = 5.17 and quality factor S = 4.34). Ca 2 AcH 16 has a T c of 165 K at 95 GPa. Our work advances the fundamental understanding of high-temperature superconductors and provides a viable strategy for the further discovery of high-temperature superconductors at ambient pressure.
Abstract Emerging altermagnets with zero net magnetic moment and momentum-dependent spin splitting offer a promising avenue for antiferromagnetic spintronic devices; yet their integration into magnetic tunnel junctions has been hindered by reliance on ferromagnetic electrodes (introducing stray fields) or by limited functionality (non-tunable magnetoresistance without spin filtering). Here, we propose an all-altermagnetic tunnel junction (AAMTJ) paradigm composed exclusively of altermagnets—exemplified by the experimentally feasible RuO 2 /NiF 2 /RuO 2 structure. By introducing an altermagnetic NiF 2 barrier, the achieved tunneling magnetoresistances of 11,704%, 2,496%, and 1,892% for RuO 2 /NiF 2 /RuO 2 are much higher than that of 221% for RuO 2 /TiO 2 /RuO 2 with a nonmagnetic TiO 2 barrier. High spin-filtering efficiencies of ∼90% are also obtained. This architecture unlocks multistate high magnetoresistance and spin filtering via magnetization control of the electrodes and barrier, stemming from their synergistic and antagonistic alignments of momentum-dependent altermagnetic spin splitting. Importantly, high tunneling magnetoresistances are still achieved in the AAMTJ with a TiO 2 spacer in the RuO 2 /TiO 2 /NiF 2 /TiO 2 /RuO 2 configuration. Our AAMTJ inherently exhibits low consumption and zero stray field, with nonrelativistic spin splitting and a vanishing magnetic moment, combining the advantages of both ferromagnetic and antiferromagnetic tunnel junctions. This AAMTJ paradigm opens an interesting avenue within the area of high-performance altermagnet-based tunnel junctions.
Biomolecules can form condensates through liquid-liquid phase separation(LLPS)to perform biological functions.It is well established that intrinsically disordered proteins play essential roles in driving LLPS,and their conformations tend to adopt more extended states within the dense phase.However,for proteins with folded structures,how the folding of individual chains and phase separation mutually influence each other remains unclear.Here,using the nucleocapsid protein 7(NCp7)of human immunodeficiency virus 1(HIV-1)and its cognate RNA as a model system,we investigated the coupling between protein folding and phase separation through coarse-grained molecular dynamics simulations.We found that the folding of NCp7 into its native structure,which contains two zinc finger(ZF)motifs,increases the multivalency of protein-RNA interactions and promotes their co-condensation.In turn,phase separation further stabilizes the native structure of the protein by facilitating non-native interactions within the condensates,where biomolecule concentration and molecular crowding are high.Additionally,RNA exhibits a highly dynamic structure,which enables it to simultaneously engage in protein interactions and adopt interchain double-stranded helical conformations,thereby mediating a balance between protein-RNA attraction and RNA-RNA repulsion.The results of this work suggest that tuning the folding and stability of individual biomolecules(e.g.,through metal-ion binding)offers an effective route to modulate biomolecular condensation,highlighting a promising strategy for drug design targeting the macroscopic phase behavior of biomolecules.
Abstract One-dimensional (1D) transition-metal dichalcogenide (TMDC) nanoribbons are appealing for a plethora of emergent physics and innovative high-tech applications unattainable with their two-dimensional (2D) and bulk counterparts. Despite notable progress in synthesizing TMDC monolayer nanoribbons, the production of TMDC heterostructure nanoribbons, which can integrate the best characteristics of the constituent monolayers, remains elusive. Here, we realize the synthesis of rhombohedral, single-crystalline WS 2 /MoS 2 nanoribbons through a multi-mechanism atomic manufacturing strategy combining vapour–solid–solid growth, vapour–liquid–solid growth, and self-etching. Over 90% of the as-produced rhombohedral WS 2 /MoS 2 nanoribbons display an axial orientation parallel to the zigzag direction, evidencing excellent chiral homogeneity and controllability. Benefiting from the rhombohedral stacking order and 1D geometric structure, spatial inversion, out-of-plane mirror, and C 3 rotational symmetries are all broken, resulting in enhanced nonlinear optical responses and the emergence of a spontaneous photovoltaic effect. Our work establishes an effective and universal multi-mechanism route for implementing stacking-controlled TMDC nanoribbons, as well as other diverse 2D-material nanoribbons, potentially outlining a bright vision for a broad portfolio of emerging quantum, electronic, and optoelectronic devices.
