When studied by small-angle neutron scattering, the vortex lattice (VL) in ${\mathrm{UPt}}_3$ undergoes a gradual disordering as a function of time due to ${}^{235}\mathrm{U}$ fission. This temporarily heats regions of the sample above the critical temperature, where, upon recooling, the vortices remain in a quenched disordered state. The disordering rate is proportional to the magnetic field, suggesting that it is governed by collective VL properties such as the elastic moduli. An ordered VL can be re-formed by applying a small field oscillation, showing that the fission does not cause detectable radiation damage to the ${\mathrm{UPt}}_3$ crystals, even after long exposure.

Strain can tailor the band structures and properties of graphene nanoribbons (GNRs) with the well-known emergent pseudomagnetic fields and the corresponding pseudo Landau levels. We design one type of the zigzag GNR with reverse strains, producing pseudomagnetic fields with opposite signs in the lower and upper half planes. Therefore, electrons propagate along the interface as “snake states,” experiencing opposite Lorentz forces as they cross the zero field border line. By using the Landauer-Büttiker formalism combined with the nonequilibrium Green's function method, the existence and robustness of the reverse strain-induced snake states are further studied. Furthermore, the realization of long-thought pure valley currents in monolayer graphene systems is also proposed in our device.

Using an effective Dirac model, we study the orbital Hall effect (OHE) in bilayers of transition metal dichalcogenides with 2H stacking (2H-TMD). We use first-order perturbation theory in the interlayer coupling of the bilayer system to obtain analytical expressions for the orbital Hall conductivity in the linear response regime. We use two distinct descriptions of the orbital angular momentum (OAM) operator. The first one is the intra-atomic approximation that considers only the intrasite contribution to the OAM [Cysne et al., Phys. Rev. Lett. 126, 056601 (2021)]. The second one uses the Berry phase formula of the orbital (valley) magnetic moment to describe the OAM operator [Bhowal and Vignale, Phys. Rev. B 103, 195309 (2021)]. This approach includes both intersite and intrasite contributions to the OAM. Our results suggest that the two approaches agree qualitatively in describing the OHE in bilayers of 2H-TMDs, although they present some quantitative differences. We also show that interlayer coupling plays an essential role in understanding the OHE in the unbiased bilayer of 2H-TMD. This coupling causes the Bloch states to become bonding (antibonding) combinations of states of individual layers, demanding the consideration of the non-Abelian structure of the orbital magnetic moment to the occurrence of OHE. As we discuss throughout the work, the emerging picture of transport of OAM in the unbiased bilayer of 2H-TMDs based on OHE is very different from the usual picture based on the valley Hall effect, shedding new light on previous experimental results. We also discuss the effect of the inclusion of a gate-voltage bias in the bilayer system. Our work gives support to recent theoretical predictions on OHE in two-dimensional materials.

The linear charge transport properties of Weyl semimetals, such as negative magnetoresistance related to chiral anomaly, have been studied extensively. In this work, the nonlinear current response of Weyl semimetals to a strong dc-ac electric field in the ultraquantum regime with a strong magnetic field is explored by employing a nonperturbative treatment based on the stochastic Liouville equation. Our systematic studies of nonlinear charge transport for two types of ac fields (the cosinusoidal electric field and the periodic pulsed field) have revealed extraordinary modulation of nonlinear current response by the ac fields. For the case with the cosinusoidal electric field, we find the following: (i) in the high-frequency regime, dynamic localization (vanishing of current) and quasienergy band collapse occur under a suitable condition of $J_0\left(\frac{e{E}_{A}d}{\hslash {\omega }_0}\right)=0$, where $J_0$ is the Bessel function with $E_A$ and ${\omega }_0$ being the strength and frequency of the ac field, and $d$ denoting the lattice constant of Weyl semimetals; and (ii) in the intermediate- and low-frequency regimes, the multiple-photon-assisted transport leads to extremal values of current responses whose patterns can be tuned by the magnetic field. As for the pulsed electric field, our results show that (i) the dynamic localization and quasienergy band collapse appear under a different condition of $cos\left(\frac{e{E}_{A}d}{\hslash {\omega }_0}\right)=0$; and (ii) the influence of the ac field on the current response disappears when $\frac{e{E}_{A}d}{\hslash {\omega }_0}=m\pi$, with $m$ being an integer. The experimental conditions are also discussed and the predicted nonlinear transport effects could be observed in experiments.

Electrons undergoing a Mott transition may shed their charge but persist as neutral excitations of a quantum spin liquid (QSL). We introduce concrete two-dimensional models exhibiting this exotic behavior as they transition from superconducting or topological phases into fully charge-localized insulators. We study these Mott transitions and the confinement of neutral fermions at a second transition into a symmetry-broken phase. In the process, we also derive coupled-wire parent Hamiltonians for a non-Abelian QSL and a ${\mathbb{Z}}_4$ QSL.

Magnetic susceptibility, specific heat, and muon spin relaxation ($\mu \mathrm{SR}$) measurements have been performed on a synthesized three-dimensional sandglass-type lattice ${\mathrm{Tm}}_3{\mathrm{SbO}}_7$, where two inequivalent sets of non-Kramers ${\mathrm{Tm}}^{3+}$ ions (${\mathrm{Tm}}_1^{3+}$ and ${\mathrm{Tm}}_2^{3+})$ show crystal electrical field effect at different temperature ranges. The existence of an ordered or a glassy state down to 0.1 K in zero field is excluded. The low-energy properties of ${\mathrm{Tm}}_3{\mathrm{SbO}}_7$ are dominated by the lowest non-Kramers quasidoublet of ${\mathrm{Tm}}_1^{3+}$, and the energy splitting is regarded as an intrinsic transverse field. Therefore, the low-temperature paramagnetic phenomenon in ${\mathrm{Tm}}_3{\mathrm{SbO}}_7$ is explained by a transverse field Ising model, which is supported by the quantitative simulation of specific heat data. In addition, the perturbation from ${\mathrm{Tm}}_2^{3+}$ may play an important role in accounting for the low temperature spin dynamics behavior observed by $\mu \mathrm{SR}$.

The stationary state of the spin Hall bar is studied in the framework of a variational approach that includes nonequilibrium screening effects at the edges. The minimization of the power dissipated in the system is performed taking into account the spin-flip relaxation and the global constraints due to the electric generator and global charge conservation. The calculation is performed within the approximations of negligible spin-flip scattering and strong spin-flip scattering. In both cases, simple expressions of the spin accumulation and the longitudinal and transverse pure spin currents are derived analytically. In usual conditions, the maximum amplitude of the spin accumulation is expected to be of the order of 1% of the equilibrium density carriers.

The fluctuation conductivity of a moderately clean type II superconductor with strong Pauli paramagnetic pair breaking (PPB) is studied by focusing on the quantum regime at low temperatures and in high magnetic fields. First, it is pointed out that, as the PPB effect becomes stronger, the quantum superconducting fluctuation is generally enhanced so that the renormalized Aslamasov-Larkin (AL) fluctuation conductivity tends to vanish upon cooling above the irreversibility line. Furthermore, by examining other [the DOS and the Maki-Thompson (MT)] terms of the fluctuation conductivity, the field dependence of the resulting total conductivity is found to depend significantly on the type of the vortex lattice (or, glass) ordered state at low temperatures where the strong PPB plays important roles. By comparing the present results on the fluctuation conductivity with insulating and negative magnetoresistance behaviors seen upon entering a PPB-induced novel SC phase of iron selenide (FeSe), it is argued that the vortex matter states of the superconducting order parameter in the second lowest $(n=1)$ Landau level are realized in FeSe in the parallel field configuration in high fields and at low temperatures.

We have performed a combined experimental and theoretical study of the ${\mathrm{Co}}_{1+x}\mathrm{MnSb}$ system to understand the progressive evolution of the crystal structure and physical properties as a function of Co content. We find that all the arc-melted polycrystalline samples show superstructure ordering similar to CoMnSb. In the CoMnSb superstructure with $Fm\text{−}3m$ symmetry, one set of the $32f$ sites is filled with Co atoms while the other set is vacant. With increasing Co content, although the vacant set of $32f$ sites gets progressively filled with the Co atoms, some of the Co atoms segregate out of the main phase into the grain boundaries. The maximum Co that enters in the ${\mathrm{Co}}_{1+x}\mathrm{MnSb}$ phase is $x=\sim 0.45$. Thus, we find that the theoretically predicted ${\mathrm{Co}}_2\mathrm{MnSb}$ in $L{2}_1$ phase does not stabilize. All the samples are ferromagnetic above room temperature and the trend in the measured magnetic moments with increasing $x$, agrees reasonably well with the density-functional theory calculations done using the structural and compositional parameters obtained from the Rietveld refinement of the synchrotron x-ray diffraction patterns. However, the electronic structure indicates that in spite of the large magnetic moment, none of the alloys are half metallic. Finally, we find that a minor deviation from stoichiometry in CoMnSb, i.e., excess of Co and Sb as compared to Mn, is accommodated in the set of vacant $32f$ sites of the superstructure. This explains the increase in the lattice parameter and the saturation magnetization, as compared to the calculated stoichiometric CoMnSb superstructure. Calculations also predict that this minor deviation from stoichiometry destroys the half metallicity in the CoMnSb superstructure.

The interfacial Dzyaloshinskii-Moriya interaction (iDMI) was observed in the bilayer consisting of a heavy metal and a ferromagnetic insulator such as $\mathrm{Pt}|{\mathrm{Tm}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}$ (TIG), but the source and origin are still controversial. Here, we quantitatively investigate the iDMI strength in Pt|TIG by inserting a thin ${\mathrm{Y}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}$ layer and/or a thin Cu layer between Pt and TIG. Our results suggest the iDMI contributed by both the Pt|TIG and the TIG|substrate interfaces. At the Pt|TIG interface, we find that Pt is essential for the strong iDMI. The disentangled iDMIs for Fe-Fe and Tm-Fe pairs are comparable, revealing that the Tm ions provide not only an additional Tm-Fe iDMI, but also the spin-orbit coupling to enhance the iDMI. At the TIG|substrate interface, the iDMI is attributed to the lattice-mismatch-induced deformation of the electron cloud for the ferromagnetic ions.

After decades of debate, now there is a rough consensus that at zero temperature the spin-$1/2$ Heisenberg antiferromagnet on the triangular lattice is three-sublattice ${120}^{\circ }$ magnetically ordered, in contrast to a quantum spin liquid as originally proposed. However, there remains considerable discrepancy in the magnetization reported among various methods. To resolve this issue, in this work we revisit this model by the tensor-network state algorithm. The ground-state energy per bond $E_b$ and magnetization per spin $M_0$ in the thermodynamic limit are obtained with high precision. The former is estimated to be $E_b=-0.18334\left(10\right)$. This value agrees well with that from the series expansion. The three-sublattice magnetic order is firmly confirmed and the magnetization is determined as $M_0=0.161\left(5\right)$. It is about $32\%$ of its classical value and slightly below the lower bound from the series expansion. In comparison with the best estimated value by Monte Carlo and density-matrix renormalization group, our result is about $20\%$ smaller. This magnetic order is consistent with further analysis of the three-body correlation. Our work thus provides benchmark results for this prototypical model.

Without applied bias voltage, a superconducting phase difference can drive a charge Josephson supercurrent in a superconductor junction. In analogy, we here theoretically propose a spin phase that intrinsically generates spin Josephson supercurrent, and this spin Josephson effect is studied in a junction of superconducting nanowire (SNW). We show that spin-orbit coupling and magnetic field give rise to spin-triplet superconductivity in the SNW, thus allowing the superfluid of both charge and spin. Next we introduce the concept of a spin phase that can be generated by controls of spin current, magnetic field, or electric field. By the analysis of pairing correlations and Ginzburg-Landau-type theory, it is shown that the spin phase makes spin-up and spin-down $S=1$ Cooper pairs get opposite phases and move oppositely in a Josephson junction, so a dissipationless pure spin current is induced. We also derive the formula that the spin current is equal to the derivative of an Andreev bound state to the spin phase, which is analogous to that of charge Josephson effect. At last, our calculation verifies the existence of spin supercurrent inside the superconducting gap in the topologically nontrivial phase. Our paper provides a view on spin Josephson effect and indicates the potential combination of topological superconductivity and spintronics.

We have carried out soft x-ray photoemission experiments on itinerant ferromagnet ${\mathrm{Sr}}_{1-x}{\left({\mathrm{La}}_{0.5}{\mathrm{K}}_{0.5}\right)}_x{\mathrm{RuO}}_3$ to investigate how the electronic state varies with doping concentration. The Ru $4d$-derived coherent part of the valence spectra develops significantly with increasing $x$ for $x⩽0.3$, which can be explained by the suppression of the ferromagnetic exchange splitting. With further increasing $x$, this development is overwhelmed by the spectral weight transfer from the coherent to the incoherent parts due to the electron correlation. The enhancement of the electron correlation effect with doping is also confirmed by the Ru $3d$ core-level spectra as the suppression of the well-screened peak. In contrast to the remarkable variation of the Ru $4d$ spectral intensity as a function of $x$, the valence spectra hardly depend on temperature and do not show any noticeable change across the magnetic transition temperatures, indicating that the temperature dependence of the exchange splitting cannot be explained by a simple Stoner picture. We compare the present photoemission results with those for isostructural ${\mathrm{Sr}}_{1-x}{A}_x{\mathrm{RuO}}_3$ ($A=\mathrm{La}$ and Ca) and discuss the origin of the difference in the magnetic property between these doped compounds.

We have used a polarized microluminescence technique to investigate photocarrier charge and spin transport in depleted $n$-type GaAs nanowires ($\approx {10}^{17}{\mathrm{cm}}^{-3}$ doping level). At 6 K, a long-distance tail appears in the luminescence spatial profile, indicative of charge and spin transport, and only limited by the length of the nanowire (NW). This tail weakly depends on excitation power and temperature. Using a self-consistent calculation based on the drift-diffusion and Poisson equations as well as on photocarrier statistics (Van Roosbroeck model), it is found that this tail is due to photocarrier drift in an internal electric field nearly two orders of magnitude larger than electric fields predicted by the usual ambipolar model. This large electric field appears because of two effects. First, for transport in the spatial fluctuations of the conduction band minimum and valence band maximum, the electron mobility is activated by the internal electric field. This implies, in a counterintuitive way, that the spatial fluctuations favor long-distance transport. Second, the range of carrier transport is further increased because of the finite NW length, an effect which plays a key role in one-dimensional systems.

Graphene with its dispersion relation resembling that of photons offers ample opportunities for applications in electron optics. The spacial variation of carrier density by external gates can be used to create electron waveguides, in analogy to optical fiber, with additional confinement of the carriers in bipolar junctions leading to the formation of few transverse guiding modes. We show that waveguides created by gating graphene with carbon nanotubes (CNTs) allow obtaining sharp conductance plateaus, and propose applications in the Aharonov-Bohm and two-path interferometers, and a pointlike source for injection of carriers in graphene. Other applications can be extended to Bernal-stacked or twisted bilayer graphene or two-dimensional electron gas. Thanks to their versatility, CNT-induced waveguides open various possibilities for electron manipulation in graphene-based devices.

We investigate spin- and valley-symmetry-broken fractional quantum Hall phases within a formalism that naturally extends the paradigm of quantum Hall ferromagnetism from integer to fractional quantum Hall states, allowing us to construct detailed phase diagrams for a large class of multicomponent states. Motivated by recent experiments on graphene aligned with a boron nitride substrate, we predict a sequence of transitions realized by increasing the magnetic field, starting from a sublattice polarized state to a valley coherent Kekulé charge density wave state and further to an antiferromagnetic phase. Moreover, for filling fractions such as $\nu =\pm \frac{1}{3}$, we predict that the system undergoes a transition at low fields, that not only differ by the spin-valley orientation of the fractionally filled flavors, but also by their intrinsic fractional quantum Hall nature. This transition is from a Laughlin-type state to a two-component Halperin-type state both with a charge density wave order. Moreover, for $\nu =\pm \frac{1}{3},\pm \frac{2}{3}$, we predict a “canted Kekulé density phase” where the spinors of integer and fractionally occupied components have different orientations in the valley Bloch sphere, in contrast to the Kekulé state for the integer quantum Hall state at neutrality where both occupied components have the same orientation in the valley Bloch sphere.

We examine the full static nonlinear optical response of uniaxially strained transition metal dichalcogenide monolayers doped with a finite carrier density in the conduction band, in the presence of disorder. We find that the customary shift current is suppressed, yet we identify a strong, valley-dependent nonreciprocal response, which we term a unidirectional valley-contrasting photocurrent (UVCP). This DC current originates from the combined effect of strain and Kramers symmetry breaking by trigonal warping, while the contributions due to individual valleys can be separated by introducing an energy offset between them by means of a magnetization. This latter fact enables one to monitor intervalley transitions. The UVCP is proportional to the mobility and is enhanced by the excitonic Coulomb interaction and intervalley scattering, as well as by a top gate bias. We discuss detection strategies in state-of-the-art experiments.

Using the first-principles calculations, we present a prediction of the nontrivial topological phase in one-dimensional (1D) ${\mathrm{Ta}}_4{\mathrm{SiTe}}_4$ with high stability further verified by the molecular dynamics simulation and phonon spectrum. In this material, the band inversion intrinsically occurs between $\mathrm{Ta}\text{−}d$ and $\mathrm{Te}\text{−}p$ orbitals without the spin-orbit coupling effect. As a novel topological insulator, protected by time-reversal symmetry Tˆ and inversion symmetry Pˆ, we explicitly demonstrate the existence of nontrivial topological invariants and the protected edge states in it with a large bulk band gap of $\sim 163\mathrm{meV}$, which could facilitate the experimental verification at the room temperature. In addition, we find its topological states are robust against the external pressure. Our results uncover a potential 1D topological-insulating ${\mathrm{Ta}}_4{\mathrm{SiTe}}_4$ and promote it as a concrete material platform for exploring the intriguing physics of low-dimensional topological phases.

Density functional theory is used to calculate the optical absorption of oxygen vacancies in potassium titanyl phosphate ($\mathrm{K}\mathrm{Ti}\mathrm{O}\mathrm{P}{\mathrm{O}}_4$, KTP) crystals. A modified hybrid functional is used for the description of the midgap defect states and the optical excitation energies. Oxygen vacancies in the $+2$ charge state lead to rather minor modification of the bulk KTP optical response, while the $+1$ and neutral charge states give rise to characteristic midgap optical absorption covering the whole near-infrared and visible spectrum. Its intensity is strongly polarization dependent and strongest for light polarized parallel to the $z$ axis. The modification of the KTP optical absorption by oxygen vacancies predicted here corroborates the picture that the gray-track formation in KTP, i.e., its photochromic damage, is related to a successive charging of oxygen vacancies.