Magnetic topological materials are a realization of topologically nontrivial electronic band structure with magnetic correlation effects; they offer novel opportunities in manipulating charge/spin transport as well as spin texture. In the search for emergent phenomena that are specific in this class of materials, here we report on a type of quantum oscillation of a polar magnetic Weyl semimetal (WSM) NdAlSi in both the temperature dependent electrical resistivity and specific heat at a constant magnetic field. It is revealed that they arise from the destructive interference between field dependent quantum oscillations of the spin-split Fermi surfaces due to the strong Weyl fermion–$4f$ electron exchange interaction combined with Rashba-Dresselhaus and Zeeman effects. Our results demonstrate that the $f$ electrons bearing magnetic WSMs possess even richer responses to external stimuli compared to known $d$-electron magnetic WSMs and call for further in-depth investigations.

A microelectromechanical oscillator with a $0.73\mu \mathrm{m}$ gap structure is employed to probe the surface Andreev bound states in superfluid ${}^3\mathrm{He}\text{−}\mathrm{B}$. The surface specularity of the oscillator is increased by preplating it with 1.6 monolayers of ${}^4\mathrm{He}$. In the linear regime, the temperature dependence of the damping coefficient is measured at various pressures, and the normalized energy gap is extracted. The damping coefficient increases after preplating at lower pressures, which is attributed to the decreased energy minigap of the surface bound states. The device is also driven into the nonlinear regime, where the temperature independent critical velocity at each pressure is measured. The critical velocity is observed to increase after preplating at all pressures, which might be related to the increased average energy gap. The observed behavior warrants a microscopic theory beyond a single parameter characterization of the surface.

We consider superconductivity in a system with $N$ Fermi surfaces, including intraband and interband effective electron-electron interactions. The effective interaction is described by an $N\times N$ matrix whose elements are assumed to be constant in thin momentum shells around each Fermi surface, giving rise to $s$-wave superconductivity. Starting with attractive intraband interactions in all $N$ bands, we show that too strong interband interactions are detrimental to sustaining $N$ nonzero components of the superconducting order parameter. We find similar results in systems with repulsive intraband interactions. The dimensionality reduction of the order-parameter space is given by the number of nonpositive eigenvalues of the interaction matrix. Using general models and models for superconducting transition metal dichalcogenides and iron pnictides frequently employed in the literature, we show that constraints must be imposed on the order parameter to ensure a lower bound on the free energy and that subsequent higher-order expansions around the global minimum are thermodynamically stable. We also demonstrate that similar considerations are necessary for unconventional pairing symmetries.

We show a method to construct model Hamiltonians for describing multiplet excitations of transition-metal impurities. Here, we treat systems of a transition metal substituting Al in $\alpha \text{−}{\mathrm{Al}}_2{\mathrm{O}}_3$. Based on the results of quasiparticle self-consistent $\mathit{GW}$ (QSGW) calculations for the systems, we construct the model Hamiltonian of $3d$ orbitals. We determine not only the crystal-field parameters, but also the parameters of effective interactions based on the theoretical correspondence between the QSGW calculations and the model Hamiltonian, and investigate the systematic change in these parameters. Finally, we discuss the structures of multiplet excitations calculated from these parameters.

Systems with strong electronic Coulomb correlations often display rich phase diagrams exhibiting different ordered phases involving spin, charge, or orbital degrees of freedom. The theoretical description of the interplay of the corresponding collective fluctuations giving rise to this phenomenology, however, remains a tremendous challenge. Here, we introduce a multichannel extension of the recently developed fluctuating field approach to competing collective fluctuations in correlated electron systems. The method is based on a variational optimization of a trial action that explicitly contains the order parameters of the leading fluctuation channels. It gives direct access to the free energy of the system, facilitating the distinction between stable and metastable phases of the system. We apply our approach to the extended Hubbard model in the weak to intermediate coupling regime where we find it to capture the interplay of competing charge density wave and antiferromagnetic fluctuations with qualitative agreement with more computationally expensive methods. The multichannel fluctuating field approach thus offers a promising route for a numerically low-cost treatment of the interplay between collective fluctuations in small to large systems.

We study the honeycomb lattice $t\text{−}J$ model using the fermionic tensor network approach. By examining the ansatz with various unit cells, we discover several different stripe states with different periods that compete strongly with uniform states. At very small doping $\delta <0.05$, we find almost degenerate uniform $d$-wave superconducting ground states coexisting with antiferromagnetic order. While at larger doping $\delta >0.05$, the ground state is an approximately half-filled stripe-ordered state, where the stripe period decreases with increasing hole doping $\delta$. Furthermore, the stripe states with the lowest variational energy always display $d_{x^2-y^2}$-wave pairing symmetry. The similarity between our results and those on the square lattice contributes to a more comprehensive understanding of doped Mott insulators.

We have studied spin polarization due to proximity effect at the interface of nonmagnetic $5d$ metal (Me = Ta, W, Re, Os, Ir, Pt, and Au) and ferrimagnetic conducting (mixed-valence) magnetite ${\mathrm{Fe}}_3{\mathrm{O}}_4$ or insulating maghemite $\gamma \text{−}{\mathrm{Fe}}_2{\mathrm{O}}_3$ using ab initio electronic structure calculations. Four variants of chemical bonding at the interfaces have been modeled. It appears that the moments induced are oriented according to spin orientation of Fe ions to which Me atoms are bonded-parallel for the direct Fe-Me exchange path and antiparallel for the Fe-O-Me superexchange. The obtained densities of states show that notable spin polarization occurs only for Me atomic plane at very vicinity of the interface with the ferrite. The effect is maximum $\sim 0.2$–0.3 ${\mu }_B$ for Pt, where slightly higher moment is induced by insulating $\gamma \text{−}{\mathrm{Fe}}_2{\mathrm{O}}_3$. Among other metals the moment of $\sim 0.1{\mu }_B$ is calculated for Ir. The moment induced in Ta is also relatively large $\sim 0.1{\mu }_B$, but with opposite sign and only in the case of Fe-Me bonding. The exceptional behavior of Pt can be associated with the position of its Fermi level ($E_F$) near the edge of the wide $5d$ band at a local peak of density of states (spin-nonpolarized DOS = 6.2 ${\mathrm{eV}}^{-1}$ per atom).

We report a study of selenospinel ${\mathrm{Cu}}_{6-x}{\mathrm{Fe}}_{4+x}{\mathrm{Sn}}_{12}{\mathrm{Se}}_{32}\left(x=0,1,2\right)$ single crystals, which crystallize in a cubic structure with the $Fd\overline{3}m$ space group, and show typical semiconducting behavior. The large discrepancy between the activation energy for electrical conductivity $E_{\rho }\left(32.3–69.8\mathrm{meV}\right)$, and for thermopower $E_{\text{S}}\left(3.2–11.5\mathrm{meV}\right)$, indicates a polaronic transport mechanism between 350 and 50 K. With decreasing temperature, it evolves into variable-range hopping conduction. Furthermore, the heat capacity shows a hump around 25(5) K and diverges from the Debye $T^3$ law at low temperatures, indicating the observation of structural glassy features in these crystalline solids.

We have investigated a periodically driven Creutz ladder in the presence of two different driving protocols, namely, a sinusoidal drive and a $\delta$ kick imparted to the ladder at regular intervals of time. Specifically, we have studied the topological properties corresponding to the trivial and the nontrivial limits of the static (undriven) case via computing suitable topological invariants. Corresponding to the case where the chiral symmetry of the ladder is intact, in addition to the zero energy modes, $\pi$ energy modes appear in both these cases. Further, two different frequency regimes of the driving protocol emerge, where the Floquet-Magnus expansion is employed particularly to study the high-frequency regime for the sinusoidal drive. Apart from the physics being identical in the high-frequency and the static scenarios, the zero energy modes show distinctive features at low and high frequencies. For the sinusoidal drive, there exists a sharp frequency threshold beyond which the zero energy modes only exist in the topological limit, while in the trivial limit, it exist only up to the same threshold frequency. In presence of the $\delta$ kick, the Creutz ladder demonstrates higher values of the topological invariant, and as a consequence, the system possesses a larger number of edge modes.

One-dimensional (1D) van der Waals (vdW) heterostructures have attracted great attention due to their excellent photoelectric properties which potentially serve as key components for next-generation optoelectronic devices. However, investigations on the photoelectric conversion properties in 1D vdW heterostructures are still in the rudimentary stage. Addressing the mechanism of the role of flexoelectricity in nanotubes and electronegativity difference of Janus materials on photoelectric properties remains challenging. In this paper, we investigate the flexoelectric effect and electronegativity difference on the photoelectric properties of 1D Janus-MoSSe/${\mathrm{WSe}}_2$ vdW heterostructures and assess their potential for solar cells through the atomic-bond-relaxation approach combined with ab initio nonadiabatic molecular dynamics simulations. We find that a 1D MoSSe/${\mathrm{WSe}}_2$ vdW heterostructure with $\mathit{AB}1$ stacking configuration exhibits ultrafast interfacial charge transfer and superior photoelectric conversion properties owing to the beneficial effects of flexoelectricity and electronegativity difference. Specifically, the photogenerated electron (hole) transfer in the 1D MoSSe/${\mathrm{WSe}}_2$ system occurs quickly, within 55 (17) fs. Moreover, the optimal power conversion efficiency of 1D MoSSe/${\mathrm{WSe}}_2$ vdW heterostructure-based solar cells can reach up to 6.25%, which is significantly higher than those of 1D ${\mathrm{MoS}}_2/{\mathrm{WSe}}_2$ (5.45%) and 2D MoSSe/${\mathrm{WSe}}_2$ (1.94%). In this paper, we provide an effective strategy for the development of high-efficiency solar cells.

Twisted layers of atomically thin two-dimensional materials support a broad range of quantum materials with engineered optical and transport properties. Transition metal dichalcogenides (TMDs) in the rhombohedral ($3R$, i.e., $0^{\circ }$ twist) crystal phase have been the focus of significant research interest in optical applications due to their particular broken inversion symmetry. Here, we report experimental and theoretical study of $\mathrm{W}{\mathrm{Se}}_2$ homobilayers obtained in stable $3R$ configuration by chemical vapor synthesis. We investigate the electronic and structural properties of these $3R\mathrm{W}{\mathrm{Se}}_2$ bilayers with $3R$ stacking using micro-Raman spectroscopy, angle-resolved photoemission nanospectroscopy measurements, and density functional theory calculations. Our results demonstrate that $\mathrm{W}{\mathrm{Se}}_2$ bilayers with $3R$ crystal phase (AB stacking) show a significant valence-band splitting at the $K$ point estimated at $550\pm 20$ meV. We derived experimentally effective hole masses of $0.48m_e$ and $0.73m_e$ at the $K$ point for upper and lower bands, respectively. Our work opens up perspectives for the development of optoelectronic and spintronic devices based on $3R$ TMD homobilayers.

We study two-terminal configurations in junctions between a topological superconducting wire with spin-orbit coupling and magnetic field, and an ordinary conductor with an embedded quantum dot. One of the signatures of the Majorana zero modes in the topological phase is a quantization of the zero-bias conductance at $G(V=0)=2e^2/h$. However, the finite size of the wires and the presence of the quantum dot in the junction generate more complicated features, which lead to deviations from this simple picture. Here, we analyze the behavior of the conductance at zero and finite bias $G\left(V\right)$ as a function of a gate voltage applied at the quantum dot in the case of a finite-length wire. We analyze the effect of the angle between the magnetic field and the orientation associated to the spin-orbit coupling. We provide a detailed description of the spectral features of the quantum wire weakly and also strongly coupled to the quantum dot and describe the conditions to have zero-energy states in these two regimes for both the topological and nontopological phases. We also analyze the concomitant behavior of the noise. We identify qualitative features that are useful to distinguish between the topological and nontopological phases. We show that in a strongly coupled quantum dot the simultaneous hybridization with the topological modes and the supragap states of the wire mask the signatures of the Majorana bound states in both the conductance and the Fano factor.

In systems with a conserved density, the additional conservation of the center of mass (dipole moment) has been shown to slow down the associated hydrodynamics. At the same time, long-range interactions generally lead to faster transport and information propagation. Here, we explore the competition of these two effects and develop a hydrodynamic theory for long-range center-of-mass-conserving systems. We demonstrate that these systems can exhibit a rich dynamical phase diagram containing subdiffusive, diffusive, and superdiffusive behaviors, with continuously varying dynamical exponents. We corroborate our theory by studying quantum lattice models whose emergent hydrodynamics exhibit these phenomena.

The emergence of near-ambient temperature superconductivity under pressure in metal hydride systems has motivated a desire to further understand such remarkable properties, specifically critical magnetic fields. ${\mathrm{YH}}_6$ is suggested to be a departure from conventional superconductivity, due to apparent anomalous behavior. Using density functional calculations in conjunction with Migdal-Eliashberg theory we show that in ${\mathrm{YH}}_6$ the critical temperature and the isotope effect under pressure, as well as the high critical fields, are consistent with strong-coupling conventional superconductivity, a property anticipated to extend to other related systems. Furthermore, strong-coupling corrections occur to the expected BCS values for the isotope effect coefficient $\left(\alpha \right)$, Ginzburg-Landau parameter $\left[{\kappa }_1\left(T\right)\right]$, London penetration depth $\left[{\lambda }_L\left(T\right)\right]$, electromagnetic coherence length $\left[\xi \right(T\left)\right]$, and the energy gap $\left({\mathrm{\Delta }}_0\right)$.

In this paper, we present an elastic model coupled with a heat propagation process in order to reproduce the out-of-equilibrium dynamics of spin crossover materials driven by femtosecond laser excitation: a multiscale out-of-equilibrium dynamics driven by pulsed laser excitation in spin-crossover materials (thermoelastic step), the thermal switching (thermal step), and the subsequent relaxation to the initial state on cooling. The simulations were performed for open boundaries two and three-dimensional samples, composed of individual molecules linked by springs, which stand for elastic interactions. This building-up of the samples allows the propagation of elastic waves, which leads to accumulation of high spin molecules towards edges at the maximum of the thermoelastic step. We first show that a simple model with a single “temperature” reproduces the thermoelastic, the thermal step and the relaxation to the original equilibrium state. However, the too slow thermalization of the lattice obtained in this model does not correspond to the experimental data. Therefore, to overcome this drawback, we consider either an inhomogeneous photoexcitation or different “temperatures” for the lattice and the spin states. The effect of the sample size, which prevents the existence of a thermal step in the case of nanoparticles is also discussed, as well as the three-dimensional model.

Critical slowing-down (CSD) has been a trademark of critical dynamics for equilibrium phase transitions of a many-body system, where the relaxation time for the system to reach thermal equilibrium or the quantum ground state diverges with system size. The time-crystal phase transition has attracted much attention in recent years for it provides a scenario of phase transition of quantum dynamics, unlike conventional equilibrium phase transitions. Here, we study critical dynamics near the Floquet time-crystal phase transition. Its critical behavior is described by introducing a temporal coarse-grained correlation function, whose relaxation time diverges at the critical point revealing the CSD. This is demonstrated by investigating the Floquet dynamics of a one-dimensional disordered spin chain. Through finite-size scaling analysis, we show that the relaxation time has a universal subexponential scaling near the critical point, in sharp contrast to the standard power-law behavior for CSD in equilibrium phase transitions. This prediction can be readily tested in present quantum simulation experiments.

A real-space observation of the distribution state of valence electrons, which is responsible for physical properties, is a key methodology to understand the relation between the structure and functions of matter. Here, we observe Mo $4d$ orbital electrons at subangstrom resolution in a pyrochlore-type oxide ${\mathrm{Nd}}_2{\mathrm{Mo}}_2{\mathrm{O}}_7$ based on the core differential Fourier synthesis (CDFS) analysis of high-energy x-ray diffraction data. The ${\mathrm{Mo}}^{4+} 4d^2$ orbital state is directly determined from the obtained valence electron density (VED) distribution. We also find a dip in the radial profile corresponding to a node of the $4d$ wave function. The VED distribution around the Nd site might be ascribed to the hybridization of neighboring O $2p$ with Nd $6s/6p/5d$ orbitals as well as the anisotropic ${\mathrm{Nd}}^{3+} 4f^3$ electrons, which cannot be reproduced by the simple j-j or $\mathit{LS}$ coupling pictures. In this paper, we demonstrate the usefulness of the CDFS analysis to investigate the orbital states in crystalline materials.

It was discovered that crystal-field excitations involving spin-flip transitions play a crucial role in controlling switchable optomagnet effects in antiferromagnetic ${\left({\mathrm{Fe}}_{0.875}{\mathrm{Zn}}_{0.125}\right)}_2{\mathrm{Mo}}_3{\mathrm{O}}_8$. However, when the flipped spins are in excited states to frustrate the balanced spin moments, the photoinduced magnetization has not occurred yet. Only after the ultrashort pulses disappear does the gigantic magnetization start to grow from a zero moment. In this study, we demonstrate that the gigantic optomagnetic effect is triggered by a two-step spin-flip process. Through the use of Kerr-effect microscopy and applications of the magnetic field, we discern between photoinduced switchable magnetization and nonswitchable demagnetization. Our experimental designs uncover all indispensable factors for the development of antiferromagnetic memory devices using insulating oxides.

The Berry curvature dipole (BCD) induced nonlinear Hall effect can appear in a material with time-reversal symmetry but breaking space-inversion symmetry. Meanwhile, a two-dimensional (2D) noncentrosymmetric superconducting material can host exotic Ising pairing that leads to an upper critical magnetic field far exceeding the Pauli paramagnetic limit. Based on first-principles electronic structure calculations and theoretical analysis, we demonstrate that the large BCDs and the Ising superconductivity can coexist in the monolayer MXene heterostructures of $T\text{−}{\mathrm{Mo}}_2\mathrm{C}/H\text{−}{\mathrm{Mo}}_2\mathrm{C}$. The large BCDs are generated by the multiple band anticrossings and the band inversions near the Fermi level. The breaking of in-plane space-inversion symmetry in these 2D superconducting heterostructures can induce an Ising-type spin-orbit coupling. Additionally, one of the superconducting heterostructures is identified as a $Z_2$ topological metal. Our work suggests that the $T\text{−}{\mathrm{Mo}}_2\mathrm{C}/H\text{−}{\mathrm{Mo}}_2\mathrm{C}$ heterostructures may serve as a promising platform to explore the nonlinear Hall effect and potential Ising superconductivity.

The influence of the valence band structure on the optical properties of quantum wells with a parabolic potential, consisting of ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ and ${\mathrm{In}}_{1-x}{\mathrm{Ga}}_x{\mathrm{As}}_y{\mathrm{P}}_{1-y}$ alloys, is studied and compared. The distribution of photogenerated carriers over the parabolic potential is found to be responsible for specific selection rules: the recombination due to only odd-indexed confined levels is observed. The reason for this is the accumulation of photogenerated holes at the center of the parabolic potential, which results in interband electron-hole recombination occurring at the center of the parabolic quantum wells. Furthermore, a specific valence band structure is found to be responsible for the magnetic-field-induced change in the photoluminescence circular polarization. In particular, at a certain magnetic field, the hybridization of the states of a heavy hole and a light hole results in the intersection of Landau levels with different spins, which leads to the observed change in the circular polarization of photoluminescence. The processes of long-term spin relaxation of heavy holes in both studied parabolic quantum wells are demonstrated, and the corresponding times are obtained.