We study superconducting transport phenomena involving the lensing effect and supercurrent in AA-stacked bilayer graphene, which is characterized by a linear gapless band with two shifted Dirac cones. Our findings indicate that cross Andreev reflection and Josephson current occur exclusively within the intracone process, while intercone scatterings are strictly prohibited. The normal/superconductor/normal junction can act as a superconducting lens for the upper and lower cones. Depending on the cone index, the transmitted electrons and holes can be focused, collimated, or diverged by adjusting the gate voltages. In the superconductor/normal/superconductor junction, due to interlayer coupling, the critical currents of the two cones exhibit distinct oscillation periods with junction width, leading to an irregular oscillation of the total critical current. Furthermore, the oscillations of the critical currents with the exchange field maintain a stable phase difference of one quarter period between the two cones. Consequently, a cone-dependent $0\text{−}\pi$ transition is achieved in this Josephson junction.

We construct the first integrable models based on the Haagerup fusion category $H_3$. We introduce a Haagerup version of the anyonic spin chain and use the boost operator formalism to identify two integrable Hamiltonians of PXP type on this chain. The first of these is an analog of the golden chain; it has a topological symmetry based on $H_3$ and satisfies the Temperley-Lieb algebra with parameter $\delta =(3+\sqrt{13})/2$. We prove its integrability using a Lax formalism, and construct the corresponding solution to the Yang-Baxter equation. We present numerical evidence that this model is gapless with a dynamical critical exponent $z\ne 1$. The second integrable model we find breaks the topological symmetry. We present numerical evidence that this model reduces to a CFT in the large volume limit with central charge $c\sim 3/2$.

Using optical technology for current injection and electromagnetic emission simplifies the comparison between materials. Here, we inject current into monolayer graphene and bulk gallium arsenide (GaAs) using two-color quantum interference and detect the emitted electric field by electro-optic sampling. We find the amplitude of emitted terahertz (THz) radiation scales in the same way for both materials even though they differ in dimension, band gap, atomic composition, symmetry, and lattice structure. In addition, we observe the same mapping of the current direction to the light characteristics. With no electrodes for injection or detection, our approach will allow electron scattering timescales to be directly measured. We envisage that it will enable exploration of new materials suitable for generating terahertz magnetic fields.

Two-dimensional (2D) magnetic materials are promising candidates for spintronics and quantum technologies. One extensively studied example is the ferromagnetic (FM) ${\mathrm{CrI}}_3$ monolayer with the honeycomb ${\mathrm{Cr}}^{3+}$ ($t_{2g}^3, S$ = 3/2) spin lattice, while ${\mathrm{VPS}}_3$ has the same honeycomb $S$ = 3/2 spin lattice (${\mathrm{V}}^{2+}, t_{2g}^3$) but displays Néel antiferromagnetism. In this paper, we study the electronic structure and particularly the contrasting magnetism of ${\mathrm{VPS}}_3$ and ${\mathrm{CrI}}_3$ monolayers, using density functional calculations, magnetic exchange pictures, maximally localized Wannier function (MLWF) analysis, and parallel tempering Monte Carlo simulations. We find that ${\mathrm{VPS}}_3$ is a Mott-Hubbard insulator but ${\mathrm{CrI}}_3$ is a charge-transfer insulator, and therefore their magnetic exchange mechanisms are essentially different. The first-nearest-neighbor (1NN) direct $d\text{−}d$ exchange dominates in ${\mathrm{VPS}}_3$, thus leading to a strong antiferromagnetic (AF) coupling. However, the formation of vanadium vacancies, associated with instability of the low-valence ${\mathrm{V}}^{2+}$ ions, suppresses the AF coupling and thus strongly reduces the Néel temperature ($T_N$) in line with experimental observation. In contrast, our results reveal that the major 1NN $d\text{−}p\text{−}d$ superexchanges in ${\mathrm{CrI}}_3$ via different channels give rise to competing FM and AF couplings, ultimately resulting in a weak FM coupling as observed experimentally. After revisiting several important superexchange channels reported in the literature, based on our MLWF and tight-binding analyses, we note that some antiphase contributions must be subtly and simultaneously considered, and thus we provide a deeper insight into the FM coupling of ${\mathrm{CrI}}_3$. Moreover, we identify and compare the major contributions to the magnetic anisotropy, i.e., a weak shape anisotropy in ${\mathrm{VPS}}_3$ and a relatively strong exchange anisotropy in ${\mathrm{CrI}}_3$. Our paper offers a comprehensive understanding of 2D magnetism using spin-orbital states and distinct exchange channels.

In antiferromagnetic insulators, spin angular momentum can be transferred even above the Néel temperature, where the material becomes a paramagnetic insulator. In this regime, spin transport takes the form of short-range spin fluctuations (paramagnons) rather than long-range spin waves. In this study, we demonstrate optically driven spin transport in a Pt/NiO/Co trilayer structure, where Pt is the spin generation layer, NiO is the spin transporting layer, and Co is the spin absorbing layer. By quantitatively comparing optically and electrically driven spin transport, we determine the interfacial coupling efficiency of 0.1 (optical) and 0.3 (electrical) and the relaxation length of 2.2 nm (optical) and 10.3 nm (electrical) of paramagnons of NiO. We attribute this discrepancy to the energy difference between the nonthermal and thermal processes.

A mechanism to enhance the magnetoelectric (ME) coupling in the noncentrosymmetric transition metal compound is exhibited utilizing the dynamic Jahn-Teller effect. It is noted that, despite lacking well-ordered magnetic ordering, the material would still be an interesting candidate for probing the ME effect. In $\mathrm{CoZnM}{\mathrm{o}}_3{\mathrm{O}}_8$, obvious anomalies were observed in the magnetic susceptibility ${\chi }_c$($T$) and heat capacity $C_p$, which move towards the high-temperature region with the increase of the magnetic field, and the width of these anomalies gradually widens, suggesting a possible Schottky anomaly. Correspondingly, the observed electric polarization and ME responses along the $c$ axis, considering the presence of a disorder-induced spin excitation continuum, indicate an intrinsic ME effect. Notably, the second-ordering and linear ME effect were obtained with increasing magnetic field along the $c$ axis, which is very different from the situation in $\mathrm{F}{\mathrm{e}}_2\mathrm{M}{\mathrm{o}}_3{\mathrm{O}}_8$ hosting a spin-flip phase transition with the magnetic field parallel to the $c$ axis. The p-d hybridization and exchange-striction mechanisms are believed to be the possible microscopic origins of the complex ME behaviors. Therefore, these results demonstrate an unconventional ME effect in materials, regardless of whether a complete magnetic ordering occurs, due to the ${\beta }_{ijk}{E}_i{H}_j{H}_k$ term of the density of stored free enthalpy, and this expands the scope of ME materials.

Cubic perovskite hydrides with the general formula of $MX{\mathrm{H}}_3$ have recently been predicted to have the potential to achieve superconductivity at ambient pressure. Here, based on first-principles calculations as well as the BCS theory, we propose that replacing the Mg in $\mathrm{KMg}{\mathrm{H}}_3$, which is an experimentally synthesized cubic perovskite hydride exhibiting insulating behavior, with Sc can give rise to a mechanically, dynamically, and kinetically stable superconductor, $\mathrm{KSc}{\mathrm{H}}_3$. Its superconducting transition temperature ($T_c$) is up to 40.37 K at ambient pressure. Further substitution of the K in ${\mathrm{KScH}}_3$ with Rb and Cs leads to structurally stable $\mathrm{RbSc}{\mathrm{H}}_3$ and $\mathrm{CsSc}{\mathrm{H}}_3$, with $T_c$'s of 32.91 and 18.64 K, respectively. Electron-phonon coupling calculations reveal that the soft modes in the intermediate-frequency region associated with the vibrations of H atoms in the phonon spectra play a non-negligible role in determining the high $T_c$'s of $M\mathrm{Sc}{\mathrm{H}}_3$ ($M$ = K, Rb, Cs). All these three perovskite hydrides are intermediate or strong BCS superconductors. Our results provide guidance for the design and study of ambient-pressure hydride superconductors and supply fundamental understanding of the superconductivity physical mechanism.

We investigate pair superfluidity in a generalized Bose-Hubbard model, extending the framework to include pair hopping and direct on-site pair interactions. Our study reveals unique features of the pair superfluid phase, such as reentrant behavior and pockets of the normal state within the superfluid region—phenomena absent in single-particle superfluid models. Through compressibility analysis, we identify Mott insulating features at zero temperature and a complex interplay between temperature, chemical potential, and pair hopping. We highlight the importance of the occupation basis size in accurately modeling pair-superfluid dynamics, demonstrating that excessive truncation leads to unphysical artifacts. Additionally, we present phase diagrams contrasting pair and single-particle superfluidity, showing the distinct nature of their respective transitions and phase boundaries. Our findings provide theoretical insights relevant to experimental platforms, such as ultracold atomic gases and Josephson junction systems, and utilize Floquet engineering as a justification for achieving and controlling pair-hopping dynamics. This paper enhances our understanding of pair superfluidity and paves the way for further exploration of complex quantum many-body systems.

The thermomagnetic Nernst effect and chiral edge states are key signatures of nontrivial topology and emerging Berry curvature in magnonic systems. Implementing atomistic spin simulations, we theoretically demonstrate the emergence of chiral magnon edge states at the boundaries of a ferromagnetic hexagonal lattice in the presence of Dzyaloshinskii-Moriya and Kitaev interactions, which are robust against nonlinear magnon interactions. In our simulations, we consider the spin parameters of ${\mathrm{CrI}}_3$ as a prototype of van der Waals magnetic layers. We show that the spin accumulation is reduced in the presence of Kitaev spin interactions compared to systems governed by Dzyaloshinskii-Moriya interactions. This reduction stems from the breaking of the $U\left(1\right)$ symmetry, which leads to a shorter spin coherence length imposed by the Kitaev interaction. We propose that measuring the angular dependence of the Nernst signal in a magnetic field provides an effective indirect method for identifying the microscopic origin of topological magnons. Our findings hold promising potential for advancing next-generation energy-harvesting Nernst materials and facilitating the integration of topological magnetic materials with spintronic-based quantum technologies.

We investigate the planar Hall effect (PHE) in topological insulators (TIs) in proximity to an altermagnet (AM). We find that, due to the interplay between altermagnetism and spin-momentum locking, in-plane magnetic fields can induce PHE in the TI surface states by modulating the anisotropy of the Fermi velocity, the characteristic vectors associated with spin-momentum locking, and the tilt of the Dirac cone. Both linear and nonlinear PHE can be significantly enhanced by the adjacent AM, particularly when the Néel vector lies within the TI surface. Notably, the planar Hall conductivities are tunable by the spin-momentum locking properties and change sign as the Néel vector rotates by ${180}^{\circ }$ in the TI surface. Therefore, the PHE can serve as a powerful tool for detecting both the Néel vector and the spin-momentum locking characteristics.

We investigate the critical behavior of the Kondo compensation in the presence of a power-law pseudogap in the density of states, $\rho \left(\omega \right)\sim {\left|\omega \right|}^{\epsilon }$. For $\epsilon <1$, generically—in the absence of particle-hole symmetry—this model exhibits a quantum phase transition from a partially screened doublet ground state to a fully screened many-body ground state upon increasing the exchange coupling $j$. At the critical point $j_{\text{c}}$, the Kondo compensation is found to scale as $\kappa (j<j_{\text{c}})=1-g\left(j\right)$ with the local $g$-factor vanishing as $g\sim |j-j_{\text{c}}{|}^{\beta }$. We combine the perturbative drone fermion method with the nonperturbative numerical renormalization group computations to determine the critical exponent $\beta \left(\epsilon \right)$, which exhibits a nonmonotonous behavior as a function of $\epsilon$. Our results confirm that the Kondo cloud builds up continuously in the presence of a weak pseudogap as one approaches the phase transition.

A generalized fluctuational electrodynamics-based many-body approach for calculating near-field radiative heat transfer (NFRHT) between nonspherical dipoles is proposed. The geometric parameters of nonspherical dipoles are implemented in the definition of the self-term of the free-space Green's function. Dipole polarizability is defined a posteriori from the free-space Green's function solution such that polarizability calculation is an optional postprocessing step rather than a required input. Both strong and weak forms of the generalized many-body approach are presented. It is shown that the approximate weak form is less computationally expensive but is only applicable to small particles characterized by size parameters less than ∼0.24. The generalized many-body method is compared against an analytical solution for NFRHT between two spheroidal dipoles. A good agreement is obtained, and the small discrepancies are ascribed to differences in approximations for multiple reflections. The generalized many-body method is then applied to analyze the near-field spectral conductance between two SiC ellipsoidal dipoles. Results reveal that changes in the orientation of one of the ellipsoidal dipoles lead to active tuning of localized surface phonon resonance by up to three orders of magnitude. Finally, the spectral radiative thermal conductivity of a metamaterial composed of 1000 $\mathrm{Si}{\mathrm{O}}_2$ ellipsoidal particles is studied. The metamaterial displays anisotropic radiative thermal conductivity, with resonance values differing by up to a factor of 2.8 between different directions. The generalized many-body model of NFRHT presented in this paper may be used to develop particle-based metamaterials with novel, engineered radiative thermal properties.

Interactions have strong effects in systems with flat bands. We examine the role of Coulomb interactions in two-dimensional chiral anisotropic quasiparticles that disperse linearly in one direction and have relatively flat bands near the neutrality point in the other direction, dispersing with an arbitrary, positive, even power law $2n\ge 2$. As in the conventional semi-Dirac case $(n=1)$, we show, using the renormalization group, that strong logarithmic divergences in the self-energy of generalized semi-Dirac fermions resum and lead to a restoration of linearity in the spectrum for arbitrary $n$ over a sizable energy window in the perturbative regime. We discuss those results in light of previous nonperturbative large-$N_f$ results and address the implications for physical observables.

We have proposed a scheme of coherent spin manipulation in a triangulene using the electric field generated by a scanning-tunneling-microscope (STM) tip. The study was inspired by successful synthesis of triangulenes and atomic-scale manipulation of STM tips. The electric-field evolutions of the energy spectra and the system's spin are obtained using both the Hartree-Fock (HF) model and the configuration-interaction (CI) model. The advantage of the CI model, compared with the HF model, is the ability to accurately describe the mixing of spin states, which is necessary for studying spin manipulation. The results show that the tip electric field can achieve both the spin depolarization and the mixing of spin states. Moreover, the energy splitting induced by the spin mixing can meet the requirement for the coherence of the spin manipulation. Our findings support the possibility of using the spin of a triangulene as a carbon-based qubit.

Magnetic materials with enhanced magnetoelectric couplings have been sought for decades to explore the deep correlation between spin orders and electric fields and to realize multifunctional, energy-efficient devices. Using a combination of first-principles simulations and spin superexchange theory, we predict an intrinsic nonvolatile magnetoelectric coupling in artificial multiferroic van der Waals heterostructures composed of $\mathrm{CrGeT}{\mathrm{e}}_3$ and breathing kagome lattice $\mathrm{N}{\mathrm{b}}_3\mathrm{C}{\mathrm{l}}_8$. Our calculations show that the interlayer spin orders can be tuned between ferromagnetic and antiferromagnetic by changing the ferroelectric phase of $\mathrm{N}{\mathrm{b}}_3\mathrm{C}{\mathrm{l}}_8$. Notably, this nonvolatile magnetoelectric coupling is robust with respect to the stacking order and layer thickness. This effect is explained by the variation in hybridization between the spin states of $\mathrm{CrGeT}{\mathrm{e}}_3$ and flat bands of the breathing kagome lattice $\mathrm{N}{\mathrm{b}}_3\mathrm{C}{\mathrm{l}}_8$ at two ferroelectric phases. The proposed nonvolatile magnetoelectric coupling and its mechanisms offer promise for the development of artificial two-dimensional multiferroic heterostructures for magnetoelectric applications.

Superconductivity beyond the conventional Bardeen-Cooper-Schrieffer framework often emerges out of a normal state that is accompanied by exotic magnetism and thereby displays many exceptional transport and thermodynamic properties. Here we report that the normal state of the heavy $d$-electron superconductor ${\mathrm{Rh}}_{17}{\mathrm{S}}_{15}$ is characterized by a weak ferromagnetism that persists up to room temperature. We show that the broad hump in its resistivity likely results from the Kondo interaction of the conduction electrons with this magnetism. By applying pressure, superconductivity is fully suppressed first. In the high-pressure regime, however, we observe a second dome of superconductivity with its maximum $T_c$ greater than the ambient pressure value, highlighting the possible unconventional superconductivity in this heavy $d$-electron sulfide.