Understanding the transport of spin current in antiferromagnetic materials is indispensable to develop antiferromagnetic spintronic devices. In this work, we study the spin current transmission through an antiferromagnetic IrMn insertion layer in a W/IrMn($t$)/CoFeB structure by measuring the spin Hall magnetoresistance (SMR) and spin-orbit torque (SOT). The temperature dependences of SMR and SOT effective fields indicate that the spin current transmission reaches its maximum at the Néel temperature of IrMn. The enhancement is ascribed to the increase in the interfacial spin mixing conductance, which is related to the maximum magnetic susceptibility of the IrMn layer at the Néel temperature. The spin transmission decreases monotonically as a function of the IrMn thickness, which is different from the case with an insulating antiferromagnetic NiO insertion layer in previous works. In addition, we found that the spin transmission through an antiferromagnetic IrMn layer is independent of the exchange bias orientation. Our results suggest that the spin current transmission through the IrMn layer (from W layer to CoFeB layer) is mainly mediated by spin-polarized electrons rather than magnons, which is likely due to the absence of the effective excitation of magnons in the IrMn layer by the spin-polarized current.

After the theoretical prediction that ${\mathrm{SmB}}_6$ is a topological Kondo insulator, there has been an explosion of studies on the ${\mathrm{SmB}}_6$ surface. However, there is not yet an agreement on even the most basic quantities such as the surface carrier density and mobility. In this paper, we carefully revisit Corbino disk magnetotransport studies to find those surface transport parameters. We first show that subsurface cracks exist in the ${\mathrm{SmB}}_6$ crystals, arising both from surface preparation and during the crystal growth. We provide evidence that these hidden subsurface cracks are additional conduction channels, and the large disagreement between earlier surface ${\mathrm{SmB}}_6$ studies may originate from previous interpretations not taking this extra conduction path into account. We provide an update of more reliable magnetotransport data than the previous one (S. Wolgast et al., Phys. Rev. B 92, 115110) and find that the orders-of-magnitude large disagreements in carrier density and mobility come from the surface preparation and the transport geometry rather than the intrinsic sample quality. From this magnetotransport study, we find an updated estimate of the carrier density and mobility of $2.71\times {10}^{13}$ (1/${\mathrm{cm}}^2$) and 104.5 (${\mathrm{cm}}^2$/$\mathrm{V}\sec$), respectively. We compare our results with other studies of the ${\mathrm{SmB}}_6$ surface. By this comparison, we provide insight into the disagreements and agreements of the previously reported angle-resolved photoemission spectroscopy, scanning tunneling microscopy, and magnetotorque quantum oscillations measurements.

We study the spin-resolved subgap transport in a triple quantum-dot system coupled to one superconducting and two ferromagnetic leads. We examine the Andreev processes in the parallel and antiparallel alignments of ferromagnets magnetic moments in both the linear and nonlinear response regimes. The emphasis is put on the analysis of the current cross-correlations between the currents flowing through the left and right arms of the device and relevant electron waiting time distributions. We show that both quantities can give important insight into the subgap transport processes and their analysis can help optimizing the system parameters for achieving the considerable Andreev current and efficient Cooper pair splitting. Strong positive values of cross-correlations are associated with the presence of tunneling processes enhancing the Cooper pair splitting efficiency, while short waiting times for electrons tunneling through distinct ferromagnetic contacts indicate fast splitting of emitted Cooper pairs. In particular, we study two detuning schemes and show that an antisymmetric shift of side quantum dots energy levels is favorable for efficient Cooper pair splitting. The analysis of spin-resolved waiting time distributions supports the performance enhancement due to the presence of ferromagnetic contacts, which is in particular revealed for short times. Finally, we consider the effect of changing the interdot hopping amplitude and predict that strong interdot correlations lead to a reduction of Andreev transport properties in low-bias limit.

We have investigated the magnetotransport properties and the topological electronic structure of the half-Heusler compound TbPtBi. Our experiments reveal an exceptionally large anomalous Hall effect (AHE) in the canted antiferromagnetic state of TbPtBi with the anomalous Hall angle reaching $\sim 0.68-0.76$, which is a few times larger than the previously reported record in GdPtBi. First-principles electronic structure and the associated anomalous Hall conductivity were computed in order to interpret the experimental results. Our analysis shows that the AHE in TbPtBi does not originate from the Weyl points but that it is driven by the large net Berry curvature produced by the anticrossing of spin-split bands near the Fermi level in TbPtBi.

We consider a contribution $w_{\text{ch}}$ to the micromagnetic energy density that is linear with respect to the first spatial derivatives of the local magnetization direction. For a generalized two-dimensional Rashba ferromagnet, we present a microscopic analysis of this contribution and, in particular, demonstrate that it cannot be expressed through Lifshitz invariants beyond the linear order in the spin-orbit coupling (SOC) strength. Terms in $w_{\text{ch}}$ beyond Lifshitz invariants emerge as a result of spin rotation symmetry breaking caused by SOC. The effects of these terms on the phase diagram of magnetic states and spin-wave dispersion are discussed. Finally, we present a classification of terms in $w_{\text{ch}}$, allowed by symmetry, for each crystallographic point group.

We explore the role played by electron doping in the electronic structure and transport properties of tetragonal FeTe using the local density approximation plus dynamical mean-field theory treatment. Semiconducting and metal-insulator crossover behavior observed in a paramagnetic and strained FeTe superconductor are shown to be driven by the interplay between multiorbital electron interactions and doping-induced normal-state massive Dirac fermions. The doping-dependent self-energy pole structure we derive is promising in the sense that it leads to results that explain why moderate electron band filling can generate orbital-selective Dirac valleys with strong electron mass enhancement consistent with experiments.

In transition metal dichalcogenides, defects have been found to play an important role, affecting doping, spin-valley relaxation dynamics, and assisting in proximity effects of spin-orbit coupling. Here we study localized states in ${\mathrm{WS}}_2$ and how they affect tunneling through van der Waals heterostructures of h-BN/graphene/ ${\mathrm{WS}}_2$/metal. The obtained conductance maps as a function of bias and gate voltage reveal single-electron transistor behavior (Coulomb blockade) with a rich set of transport features including excited states and negative differential resistance regimes. Applying a perpendicular magnetic field, we observe a shift in the energies of the quantum levels and information about the orbital magnetic moment of the localized states is extracted.

In this work, we theoretically investigate the optical properties of a topological-insulator nanoparticle–quantum emitter dimer interacting in the strong-coupling regime. The calculations are based on a recently developed semianalytical technique based on a multiple-scattering polaritonic-operator formalism in conjunction with an electromagnetic coupled dipole method. We calculate the light spectrum of the above dimer and report the emergence of a mode that stems from the coupling of the surface topological particle polariton of the topological insulator with the resonance state of the quantum emitter.

Dirac matters provide a platform for exploring the interplay of their carriers with other quantum phenomena. ${\mathrm{Sr}}_{1-x}{\mathrm{Mn}}_{1-y}{\mathrm{Sb}}_2$ has been proposed to be a magnetic Weyl semimetal and provides an excellent platform to study the coupling between Weyl fermions and magnons. Here, we report comprehensive inelastic neutron scattering (INS) measurements on single crystals of ${\mathrm{Sr}}_{1-x}{\mathrm{Mn}}_{1-y}{\mathrm{Sb}}_2$, which have been well characterized by magnetization and magnetotransport measurements, both of which demonstrate that the material is a topologically nontrivial semimetal. The INS spectra clearly show a spin gap of $\sim 6$ meV. The dispersion in the magnetic Mn layer extends up to about 76 meV, while that between the layers has a narrow band width of 6 meV. We find that the linear spin-wave theory using a Heisenberg spin Hamiltonian can reproduce the experimental spectra with the following parameters: a nearest-neighbor ($S{J}_1\sim 28.0$ meV) and next-nearest-neighbor in-plane exchange interaction ($S{J}_2\sim 9.3$ meV), interlayer exchange coupling ($S{J}_c\sim -0.1$ meV), and spin anisotropy constant ($SD\sim -0.07$ meV). Despite the coexistence of Weyl fermions and magnons, we find no clear evidence that the magnetic dynamics are influenced by the Weyl fermions in ${\mathrm{Sr}}_{1-x}{\mathrm{Mn}}_{1-y}{\mathrm{Sb}}_2$, possibly because that the Weyl fermions and magnons reside in the Sb and Mn layers separately, and the interlayer coupling is weak due to the quasi-two-dimensional nature of the material, as also evident from the small $S{J}_c$ of $-0.1$ meV.

The upper critical field of multiband superconductors is an important quantity that can reveal details about the nature of the superconducting pairing. Here we experimentally map out the complete upper-critical-field phase diagram of a stoichiometric superconductor, ${\mathrm{CaKFe}}_4{\mathrm{As}}_4$, up to $90\mathrm{T}$ for different orientations of the magnetic field and at temperatures down to $4.2\mathrm{K}$. The upper critical fields are extremely large, reaching values close to $\sim 3T_{\mathrm{c}}$ at the lowest temperature, and the anisotropy decreases dramatically with temperature, leading to essentially isotropic superconductivity at $4.2\mathrm{K}$. We find that the temperature dependence of the upper critical field can be well described by a two-band model in the clean limit with band-coupling parameters favoring intraband over interband interactions. The large Pauli paramagnetic effects together with the presence of the shallow bands is consistent with the stabilization of an FFLO state at low temperatures in this clean superconductor.

${\mathrm{EuCd}}_2{\mathrm{As}}_2$ is a magnetic semimetal that has the potential of manifesting nontrivial electronic states, depending on its low temperature magnetic ordering. Here, we report the successful synthesis of single crystals of ${\mathrm{EuCd}}_2{\mathrm{As}}_2$ that order ferromagnetically or antiferromagnetically depending on the level of band filling, thus allowing for the use of magnetism to tune the topological properties within the same host. We explored their physical properties via magnetization, electrical transport, heat capacity, and angle-resolved photoemission spectroscopy measurements and conclude that ${\mathrm{EuCd}}_2{\mathrm{As}}_2$ is an excellent, tunable system for exploring the interplay of magnetic ordering and topology.

Toroidal spin arrangements are emerging as promising candidates for the realization of quantum state manipulation in single molecule magnets (SMM). Being protected by weak short-range interactions, they are formed spontaneously due to simultaneous time- and space-inversion symmetry breaking. While according to the Mermin-Wagner theorem, the toroidal moment vanishes in the thermodynamic limit, the toroidal ground states could still exist in finite spin systems, remarkably, in magnetic trimers as our exact diagonalization reveals. Here we demonstrate a mechanism with which toroidal states can be induced and controlled externally using an electric field by the interplay of the spin-orbit coupling and the Aharonov-Casher effect. Conditions for the observation using the Landau-Zener-Stückelberg interferometry are identified. A control of symmetry-broken toroidal magnetic states in spin rings with Heisenberg exchange interactions is demonstrated as a paradigm for the quantum state manipulation.

We find that an atomically thin $\mathrm{Mo}{\mathrm{S}}_2$ monolayer with squared pentagon structure motifs, distinct from all the conventional $\mathrm{Mo}{\mathrm{S}}_2$ monolayers, has unique electronic band structures with Dirac cones comprising $d$ orbitals. The squared pentagon $\mathrm{Mo}{\mathrm{S}}_2$ monolayer is an intrinsic ferromagnet with a high Curie temperature and behaves as a half semimetal, which possesses spin-polarized Dirac fermions around the Fermi level. Moreover, when spin-orbit couplings are included, the magnetic Dirac band is gapped, hosting quantized conductance channels. This work provides insights in achieving two-dimensional topological materials with unique atomistic patterns.

We investigate magnetization dynamics in asymmetric interlayer exchange coupled Py/Ru/Py trilayers using both vector network analyzer–based and electrically detected ferromagnetic resonance techniques. Two different ferromagnetic resonance modes, in-phase and out-of-phase, are observed across all three regimes of the static magnetization configurations, through antiparallel alignment at low fields, the spin-flop transition at intermediate fields, and parallel alignment at high fields. The nonmonotonic behavior of the modes as a function of the external field is explained in detail by analyzing the interlayer exchange and Zeeman energies and is found to be solely governed by the interplay of their dynamical components. In addition, the linewidths of both modes were determined across the three regimes and the different behaviors of the linewidths versus external magnetic field are attributed to mutual spin pumping induced in the samples. Interestingly, the difference between the linewidths of the out-of-phase and in-phase modes decreases at the spin-flop transition and is reversed between the antiparallel and parallel aligned magnetization states.

We present a 2D bosonization duality using the language of tensor networks. Specifically, we construct a tensor network operator (TNO) that implements an exact 2D bosonization duality. The primary benefit of the TNO is that it allows for bosonization at the level of quantum states. Thus we use the TNO to provide an explicit algorithm for bosonizing fermionic projected entangled pair states (fPEPs). A key step in the algorithm is to account for a choice of spin structure, encoded in a set of bonds of the bosonized fPEPS. This enables our tensor network approach to bosonization to be applied to systems on arbitrary triangulations of orientable 2D manifolds.

One of the most significant drawbacks of the all-electron ab initio diffusion Monte Carlo (DMC) is that its computational cost drastically increases with the atomic number ($Z$), which typically scales with $Z^{\sim 6}$. In this study, we introduce a very efficient implementation of the lattice regularized diffusion Monte Carlo (LRDMC), where the conventional time discretization is replaced by its lattice space counterpart. This scheme enables us to conveniently adopt a small lattice space in the vicinity of nuclei, and a large one in the valence region, by which a considerable speedup is achieved, especially for large atomic number $Z$. Indeed, the computational performances of the improved LRDMC can be theoretically established based on the Thomas-Fermi model for heavy atoms, implying the optimal $Z^{\sim 5}$ scaling for all-electron DMC calculations. This improvement enables us to apply the DMC technique even for superheavy elements ($Z\ge 104$), such as oganesson ($Z=118)$, which has the highest atomic number of all synthesized elements so far.

Noble-metal surfaces (Au, Ag, Cu, etc.) have been extensively studied for Shockley-type surface states (SSs). Very recently, some of these Shockley SSs have been understood from the topological consideration, with the knowledge of global properties of electronic structure. In this paper, we show the existence of Dirac-like excitations in the elemental noble-metal Ru, Re, and Os based on symmetry analysis and first-principles calculations. The unique SS-driven Fermi arcs have been investigated in detail for these metals. Our calculated SSs and Fermi arcs are consistent with the previous transport and photoemission results. We attribute this Dirac excitation-mediated Fermi arc topology as the possible reason for several existing transport anomalies, such as large nonsaturating magnetoresistance, the anomalous Nernst electromotive force and its giant oscillations, magnetic breakdown, etc. We further show that the Dirac-like excitations in these elemental metals can further be tuned to three component Fermionic excitations, using a symmetry-allowed alloy mechanism.