Tunneling spectroscopy between parallel two-dimensional (2D) electronic systems provides a powerful method to probe the underlying electronic properties by measuring tunneling conductance. In this work, we present a theoretical framework for spin transport in 2D-to-2D tunneling systems, driven by spin pumping. This theory applies to a vertical heterostructure where two layers of metallic 2D electron systems are separated by an insulating barrier, with one layer exchange coupled to a magnetic layer driven at resonance. Utilizing a nonperturbative Floquet-Keldysh formalism, we derive general expressions for the tunneling spin and charge currents across a broad range of driving frequencies, extending beyond the traditional adiabatic pumping regime. At low frequencies, we obtain analytical results that recover the known behaviors in the adiabatic regime. However, at higher frequencies, our numerical findings reveal significant deviations in the dependence of spin and charge currents on both frequency and precession angle. This work offers fresh insights into the role of magnetization dynamics in tunneling transport, opening up new avenues for exploring nonadiabatic spin pumping phenomena.

Understanding heat transfer at extreme near-field scales is crucial for advancing thermal management at nanoscale and subnanoscale levels, where traditional continuum theories often fail. However, existing studies have mainly focused on larger gap sizes $(>10\AA )$, and the transition between radiative and conductive mechanisms in the extreme near-field remains underexplored. To fill this gap, we use nonequilibrium molecular dynamics (NEMD) simulations to investigate heat transfer between two plates with vacuum gaps ranging from 0.5 to 7 Å. The choice of $3C$-SiC is motivated by its well-defined dielectric properties and relevance in nanotechnology. By using dielectric responses derived from equilibrium molecular dynamics simulations, we compare both local and nonlocal near-field radiative heat transfer with NEMD results and reveal significant deviations from continuum theory in the extreme near-field regime. Subsequently, we analyze the scaling behavior of thermal conductance with gap distance, identifying a power-law decay of $d^{-1.48}$ for gaps smaller than 3.8 Å and $d^{-5.37}$ for larger gaps, influenced by the interplay of the Vashishta potential, atomic interaction strength related to the lattice constant, and the system's tendency to minimize potential energy through gap relaxation. Moreover, due to lattice anharmonicity, energy transmission across the nanogap increases with rising temperature, as demonstrated by further simulations. These results provide insights into energy transfer mechanisms in the extreme near field and suggest directions for future research.

We present a theoretical model describing a Josephson junction featuring a magnetically textured barrier within two-dimensional (2D) $p$-wave superconductor, considering both ($p_x+p_y$)- and ($p_x+i{p}_y$)-type pairing symmetries. Our study reveals the influence of the magnetic barrier strength and its spatial periodicity on the system's topological properties, in terms of local density of states and Josephson current calculations. Notably, we demonstrate that these parameters regulate the number of Majorana zero modes at the junction in the topological regime. Our setup further allows for the identification of three distinct topological phases, the differentiation between one-dimensional (1D) Majorana edge (either flat or dispersive and arising from intrinsic 2D $p$-wave pairing) and localized Majorana end modes, and an analysis of their hybridization through the Josephson current. In particular, the Josephson current exhibits a discontinuous jump due to the edge modes and pronounced hump in the $p_x+i{p}_y$ pairing case, directly linked to the hybridized Majorana modes. Moreover, our study opens a possible interesting avenue to distinguish between 1D Majorana edge modes and zero-dimensional end modes via Josephson current signatures.

We study the formation of subgap impurity states in strongly correlated Mott insulators. We use a composite operator method that gives us access to both the bulk Green's function, as well as to the real-space Green's function in the presence of an impurity. Similar to the noninteracting systems, we show that the formation of impurity subgap states at large impurity potential (“Mott ring states”) depends rather on the band mixing than on the topological character of the system. Thus, even a trivial Mott insulator can under certain conditions exhibit ring states. For the system studied here the band mixing is that between the holon and doublon elementary excitations rather than an orbital mixing. Moreover, we study the formation of bands of zeros in the correlated Green's function, believed to exhibit a free quasiparticlelike behavior. We show that in the presence of an impurity the same conclusion can be applied, i.e., “Mott zeros' ring states” form in the presence of topological bands of zeros, but also for trivial quasiflat bands of zeros with band mixing.

We study the quantum dynamics of a strongly correlated electron pair in a one-dimensional lattice, focusing on the occurrence of local dissociation/pairing mechanisms induced by a site energy defect. To this end, we simulate the time evolution of two interacting electrons on a finite-size chain governed by an extended Hubbard Hamiltonian including on-site Coulomb repulsion $U$ and nearest-neighbor interaction $V$, along with single-electron hopping $J$. By introducing a local site energy defect with amplitude $\mathrm{\Delta }$, we show that a transition between spatially paired/dissociated electrons can occur in the vicinity of this site. Such mechanisms arise in a strongly correlated regime with nonzero nearest-neighbor Coulomb interactions and under the conditions $(U\sim V\sim \mathrm{\Delta })\gg J$. To rationalize these phenomena, we reformulate the two-electron dynamics of the original Hubbard chain as an effective single-particle problem on a two-dimensional network. Within this framework, we show that the pairing/dissociation dynamics are driven by resonances between two distinct families of two-electron eigenstates: (i) states with two spatially well-separated electrons with one located at the site defect, and (ii) states with a locally bound electron located away from the defect. At resonance, these states hybridize, allowing transitions from locally paired to dissociated electrons—and vice versa—in the vicinity of the defect. These results provide further insights into exotic pairing phenomena in strongly correlated electronic systems and may have implications for the design of tunable many-body states in low-dimensional quantum materials.

We propose twisted homobilayer of a carbon allotrope, ${\mathrm{C}}_{568}$, to be a promising platform to realize a controllable square lattice single-band extended Hubbard model. This setup has the advantage of a widely tunable $t^{\prime }/t$ ratio without adding external fields, and the intermediate temperature $t\ll T\ll U$ regime can be easily achieved. We first analyze the continuum model obtained from symmetry analysis and first-principle calculations, and calculate the band structures. Subsequently, we derive the corresponding tight-binding models and fit the hopping parameters as well as the Coulomb interactions. When a displacement field is applied, anisotropic nearest-neighbor hoppings can further be achieved. If successfully fabricated, the device could be an important stepping stone towards understanding high-temperature superconductivity.

Recent advancements in two-dimensional van der Waals (vdW) ferroelectric materials have highlighted the significance of both interlayer and intralayer degrees of freedom in governing their functional properties. Among these, ${\mathrm{CuInP}}_2{\mathrm{S}}_6$ (CIPS) stands out due to the unique displacement behavior of ${\mathrm{Cu}}^{+}$ ions within the layers and across the vdW gap in the layered CIPS structure. In this work, we present a comprehensive first-principles study of the structural, vibrational, ferroelectric, and electronic properties of CIPS under hydrostatic pressure (0–18 GPa). Our calculations predict a pressure-induced structural transition from the monoclinic $Cc$ phase to a trigonal $P31c$ phase above 6.8 GPa. At higher pressures, a metastable centrosymmetric $P\overline{3}1c$ phase can be stabilized, which serves as the paraelectric reference for the ferroelectric $P31c$ phase. Our lattice dynamics analysis reveals two zone-center instabilities, polar ${\mathrm{\Gamma }}_2^{-}$ and antipolar ${\mathrm{\Gamma }}_2^{+}$, in the centrosymmetric reference $P\overline{3}1c$ structure, leading to the identification of distinct ferroelectric ($P31c$) and antipolar ($P\overline{3}$) phases. By mapping the two-dimensional potential energy surface as a function of these two lattice instabilities, we further identify a low-energy-barrier polarization switching pathway for the ferroelectric $P31c$ phase, with the antipolar $P\overline{3}$ phase serving as an intermediate state, supporting the theory of asynchronous switching mechanism in CIPS. Using the modern theory of polarization, we distinguish between low- and high-polarization variants of the $P31c$ phase. Electronic structure analysis shows pressure-induced band-gap narrowing and a transition from direct to indirect gap, while retaining semiconducting character. These results provide key insights for designing pressure-tunable ferroelectric and electronic functionalities in layered materials, and highlight their potential for applications in nonvolatile memory, pressure-sensitive sensors, and flexible electronics.

Enhancement and peaks in near-field radiative heat transfer (NFRHT) typically arise due to surface phonon-polaritons, plasmon-polaritons, and electromagnetic (EM) modes in structured materials. However, the role of material quantum coherence in enhancing near-field radiative heat transfer remains unexplored. Here, we uncover that NFRHT in superconductor-ferromagnetic systems displays a unique peak at the superconducting phase transition that originates from the quantum coherence of Bogoliubov quasiparticles in superconductors. Our theory takes into account evanescent EM radiation emanating from fluctuating currents associated with Cooper pairs and Bogoliubov quasiparticles, in stark contrast to the current-current correlations induced by free electrons in conventional conductors. Our proposed NFRHT configuration exploits ferromagnetic resonance at frequencies deep inside the superconducting band gap to isolate this superconducting coherence peak. Furthermore, we reveal that Cooper pairs and Bogoliubov quasiparticles have opposite effects on near-field thermal radiation and isolate their effects on many-body radiative heat transfer near superconductors. Our proposed phenomenon could have applications for developing thermal isolators and heat sinks in superconducting circuits.

Ferrorotationally ordered materials possess a planar chiral lattice of electric dipoles that are a promising platform for exhibiting directionally asymmetric response functions. A key characteristic of such order is that enantiomorph conversion occurs when the solid is flipped by ${180}^{\circ }$ about an in-plane axis. Using second-harmonic interferometry, we show here that when circularly polarized light is incident on ${\mathrm{MnTiO}}_3$, the generated harmonic intensity depends on whether the incident light is parallel or antiparallel to the ferrorotational axis. For a particular photon helicity, constructive interference occurs in one direction while destructive interference occurs in the other. Our observations represent a fundamentally new optical effect, associated with circularly polarized light in ferrorotational solids, that is distinct from conventional optical activity observed in three-dimensional chiral and Faraday media.

The nondissipative quasistatic longitudinal optical response of insulators is characterized by an intrinsic geometric capacitance, determined by the ratio of the quantum metric to the energy gap, as recently established. We study the photonic spin Hall effect (PSHE) in this low-frequency regime, induced by reflection from an atomically thin material serving as the interface between two dielectrics. As a function of the magnitude of this geometric capacitance, covering values typical of graphene-family systems and for incidence close to the Brewster angle, the calculated in-plane and transverse beam shifts become comparable to the wavelength and thus detectable. At sufficiently low frequencies, we derive linear and quadratic approximations that allow the geometric capacitance to be extracted from measurements of the beam displacements. We provide upper bounds for the beam shifts. The results suggest that THz PSHE might be a useful probe of the quantum geometric capacitance of two-dimensional insulators.

Polymeric nitrogen (polynitrogen) is attractive candidate for high-energy-density materials due to the significant energy stored in nitrogen-nitrogen bonds. We firstly reported two two-dimensional layered polynitrogen structures (Amm2-${\mathrm{CN}}_6$ and Amm2-${\mathrm{CN}}_{10}$) using the ${\mathrm{C}}_2{\mathrm{N}}_8$ cage as the building blocks. The layered structures of Amm2-${\mathrm{CN}}_6$ exhibits the tunable size capabilities, as its monolayer can be exfoliated and restacked under ambient conditions. Besides, substituting carbon atoms with boron to introduce holes in Amm2-${\mathrm{CN}}_6$ transforms the material from a semiconductor into a superconductor, achieving a ${\mathrm{T}}_c$ of 7.1 K at ambient pressure. In addition, both Amm2-${\mathrm{CN}}_6$ and Amm2-${\mathrm{CN}}_{10}$ exhibit the outstanding energetic and explosive properties, with respective energy densities of 8.1 and 8.9 kJ/g, detonation velocities of 10.4 and 8.8 km/s, and detonation pressures of 60.9 and 44.9 GPa. These findings offer valuable insights for the design of advanced energetic and superconducting polynitrogen compounds.

Thermodynamic and magnetic properties as well as simulation of molecular dynamics of the Gd complex $\left[\mathrm{Gd}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6{\mathrm{Cl}}_2\right]\mathrm{Cl}$ are reported. The investigation of static susceptibility, magnetization, and electron paramagnetic resonance enabled the identification of the studied complex as an $S=7/2$ magnet with easy-axis anisotropy $D/k_B=-0.12\mathrm{K}$, rhombic anisotropy $E/D=0.008$, and effective magnetic interaction of maximal size $|J/k_B|\approx 12\mathrm{mK}$ of predominantly dipolar origin. Simulation of molecular dynamics suggests the presence of local low-energy vibrational modes with energies below $200{\mathrm{cm}}^{-1}$. Their existence is also indirectly supported by the analysis of lattice specific heat. The study of magnetic field–induced slow relaxation revealed the existence of two relaxation channels. The former is represented by extremal slow relaxation reaching a timescale of seconds, which was attributed to the coexistence of Raman and Orbach-like processes in a multilevel system in which degeneracy of Gd(III) ion doublets is lifted by static magnetic field. The latter process is effectively described by $\tau \approx T^{-2.18}$, deviating from the temperature dependence $\tau \approx T^{-3}$, which, as recently theoretically proposed, arises from the coexistence of standard Raman relaxation for a multilevel system with $\tau \approx T^{-5}$ and the interaction of Gd(III) ions with local low-energy vibrational modes. In addition, the magnetic field dependence of the relaxation time reveals a pronounced acceleration of dynamical response with increasing magnetic field, suggesting resonant phonon trapping as the dominant relaxation mechanism. The present work suggests that the interaction of a magnetic ion with local low-energy vibrational modes proposed as the origin of anomalous Raman relaxation in single-molecule magnets, despite the presence of local vibrational modes in the system, may not occur as the main relaxation mechanism.

The generation of collinear spin current (CSC) in the out-of-plane direction, where both the propagation direction and spin-polarized direction aligned perpendicularly to the applied charge current, is crucial for efficiently manipulating systems with perpendicular magnetic anisotropy used in high-density magnetic recording. However, the efficient generation of CSC remains a challenge. In this work, based on the symmetry analysis, we propose that CSC can be effectively generated using altermagnets when the charge current is aligned along specific directions, due to spin-dependent symmetry breaking. This proposal is supported by density functional theory and Boltzmann transport equation calculations on a series of altermagnetic materials, including ${\mathrm{RuO}}_2, {\mathrm{Mn}}_5{\mathrm{Si}}_3, {\mathrm{KRu}}_4{\mathrm{O}}_8$, and ${\mathrm{CuF}}_2$, where unusually large CSC is produced by the charge current along certain orientations. Furthermore, we introduce a physical quantity, the spin-splitting angle, to quantify the efficiency of CSC generated by the charge current. We find that the spin-splitting angle ranges from 0.24 to 0.57 in these altermagnets, which is significantly larger than the spin-Hall angle typically observed in the anomalous spin-Hall effect, where the spin-Hall angle is generally less than 0.1. Our findings provide an effective method for manipulating spin currents, which is advantageous for the exploration of altermagnetic spintronic devices with field-free perpendicular magnetization switching.

Nodal noncentrosymmetric superconductors can host zero-energy flat bands of Majorana surface states within the projection of the nodal lines onto the surface Brillouin zone. Thus, these systems can have stationary, localized Majorana wave packets on certain surfaces, which may be a promising platform for quantum computation. Such applications require protocols to manipulate the wave packets in order to move them without destroying their localization or coherence. As a step in this direction, we explore the idea that the surface states have a nontrivial spin polarization, which can couple for example to the magnetization of a ferromagnetic insulator in contact to the surface, via an exchange term in the Hamiltonian. Such a coupling can make the previously flat bands weakly dispersive. We aim to model the motion of spatially localized wave packets under the influence of an exchange field which is changed adiabatically. We calculate the time-evolved wave packet for a model system and discuss which factors influence the direction of motion and the broadening of the wave packet.

Topologically protected edge states, immune to various disorders, have been realized in a range of topological insulators. In this article we demonstrate that Landau levels in aperiodic acoustic structures can be realized under different pseudomagnetic fields (PMFs). The resulting zero-order Landau modes (ZOLMs) can propagate along the channels at the interior or exterior of the inhomogeneous array, referred to as “bulk-transport states” (BTSs) and “edge-transport states” (ETSs), respectively. Unlike conventional valley edge states, the ZOLMs exhibit a fascinating self-collimation feature. Additionally, when a pseudoelectric field (PEF) is introduced, the combination of a PMF and PEF leads to the formation of bulk or edge Landau rainbows, where the zeroth Landau modes are distributed at various positions within the bulk or boundary of the sample at different frequencies. These synthetic-gauge-field-controlled topological states enable full control over robust transmission, utilizing the entire footprint of a topological lattice. Our findings not only significantly advance the understanding of topological phase matter but also open up new possibilities for the design of topological acoustic devices.

The molecular-to-atomic liquid-liquid transition (LLT) in high-pressure hydrogen is a fundamental topic touching domains from planetary science to materials modeling. Yet, the nature of the LLT is still under debate. To resolve it, numerical simulations must cover length and time scales spanning several orders of magnitude. We overcome these size and time limitations by constructing a fast and accurate machine-learning interatomic potential (MLIP) built on the MACE neural network architecture. The MLIP is trained on Perdew-Burke-Ernzerhof (PBE) density functional calculations and uses a modified loss function correcting for an energy bias in the molecular phase. Classical and path-integral molecular dynamics driven by this MLIP show that the LLT is always supercritical above the melting temperature. The position of the corresponding Widom line agrees with previous ab initio PBE calculations, which in contrast predicted a first-order LLT. According to our calculations, the crossover line becomes a first-order transition only inside the molecular crystal region. These results call for a reconsideration of the LLT picture previously drawn.

Materials and devices subject to spatiotemporal modulation of their effective properties have a demonstrated ability to support nonreciprocal transmission of waves. Most notably, spatiotemporally modulated systems can restrict wave transmission to only one direction, i.e., a very large difference in the energy transmitted between two points in opposite directions. Taking on a different perspective on nonreciprocity, we present a response regime in spatiotemporally modulated systems that is characterized by equal transmitted amplitudes (energies) but different phases. The only contributor to nonreciprocity is therefore the nonreciprocal phase shift, the difference between the transmitted phases in the opposite directions. We develop a methodology for realization of nonreciprocal phase shifts based on the response envelopes. This includes a formulation that ensures the same transmitted waveform, along with a special case of near-reciprocal transmission. We focus primarily on steady-state vibration transmission in short, weakly modulated systems but include a special case of nonreciprocal phase shifts for systems with arbitrary length and strength of modulation. We discuss the main limitations of our methodology as well as a pathway to overcome it to motivate further developments on strongly modulated systems. While showcasing a way for controlling vibration information transmission, our findings highlight the potential role of phase as an additional parameter in nonreciprocal transmission in spatiotemporally modulated systems.

An efficient and scalable implementation of a method for locating first-order saddle points on the energy surface of a magnetic system is presented, along with several applications in which the mechanisms of various magnetic transitions are identified. The starting point for the iterative search algorithm can be anywhere, even close to a local energy minimum representing an initial state of the system, and the final state need not be specified. Convergence on a saddle point is obtained by inverting the component of the gradient along the minimum mode, thereby effectively transforming the neighborhood of the saddle point to that of a local minimum. The method requires only the lowest two eigenvalues and corresponding eigenvectors of the Hessian of the system's energy and they are found using a quasi-Newton limited-memory Broyden-Fletcher-Goldfarb-Shanno solver for the minimization of the Rayleigh quotient without explicit evaluation of the Hessian. The method is applicable to large systems, as it does not introduce additional scaling overhead to the computational complexity determined by the interactions present in the system. Applications are presented to transitions in systems that reveal significant complexity of coexisting magnetic states, such as skyrmions, skyrmion bags, skyrmion tubes, chiral bobbers, and globules. The identification of new metastable three-dimensional (3D) textures, such as magnetic bobbers with extended equilibrium distance between the base and the terminating Bloch point, and magnetic globules appearing as isolated states in 3D due to magnetostatic interactions, demonstrates the usefulness of the method for the characterization of complex energy surfaces of magnetic systems. When combined with rate theory within the harmonic approximation, the method can be used for simulations of the long timescale dynamics of complex magnetic systems characterized by multiple metastable states.

Superdiffusive transport with dynamical exponent $z=3/2$ has been firmly established at finite temperature for a class of integrable systems with a non-Abelian global symmetry $G$. On the inclusion of integrability-breaking perturbations, diffusive transport with $z=2$ is generically expected to hold in the limit of late time. Recent studies of the classical Haldane-Ishimori-Skylanin model have found that perturbations that preserve the global symmetry lead to a much slower time scale for the onset of diffusion, albeit with uncertainty over the exact scaling exponent. That is, for perturbations of strength $\lambda$, the characteristic timescale for diffusion goes as $t_{*}\sim {\lambda }^{-\alpha }$ for some $\alpha$. Using large-scale matrix product state simulations, we investigate this behavior for perturbations to the canonical quantum model showing superdiffusion: the $S=1/2$ quantum Heisenberg chain. We consider a ladder configuration and look at various perturbations that either break or preserve the $SU\left(2\right)$ symmetry, leading to scaling exponents consistent with those observed in one classical study [McCarthy et al., Phys. Rev. B 110, L180301 (2024)]: $\alpha =2$ for symmetry-breaking terms and $\alpha =6$ for symmetry-preserving terms. We also consider perturbations from another integrable point of the ladder model with $G=SU\left(4\right)$ and find consistent results. Finally, we consider a generalization to an $SU\left(3\right)$ ladder and find that the $\alpha =6$ scaling appears to be universal across superdiffusive systems when the perturbations preserve the non-Abelian symmetry $G$.