Pyrochlore Oxide Hg2Os2O7 on Verge of Metal–Insulator Boundary

Semimetallic osmium pyrochlore oxide Cd2Os2O7 undergoes a magnetic transition to an all-in-all-out (AIAO)-type order at 227 K, followed by a crossover to an AIAO insulator at around 210 K. Here, we studied the isostructural and isoelectronic compound Hg2Os2O7 through thermodynamic measurements, µSR spectroscopy and neutron diffraction experiments. A similar magnetic transition, probably to an AIAO-type order, was observed at 88 K, while the resistivity showed a decrease at the transition and remained metallic down to 2 K. Thus, the ground state of Hg2Os2O7 is most likely an AIAO semimetal, which is analogous to the intermediate-temperature state of Cd2Os2O7. Hg2Os2O7 exists on the verge of the metal–insulator boundary on the metal side and provides an excellent platform for studying the electronic instability of 5d electrons with moderate electron correlations and strong spin–orbit interactions.

Collapse of quasi-two-dimensional symmetrized Dresselhaus spin-orbit coupled Bose–Einstein condensate

Here, we study the collapse process of quasi-two-dimensional Bose–Einstein condensate with symmetrized Dresselhaus spin–orbit coupling. We show that at a sufficiently strong spin–orbit coupling the arising spin-dependent velocity compensates the attraction between particles and can prevent the collapse of the condensate. As a result, spin–orbit coupling can lead to a stable condensate rather than the collapse process.

Enhanced thermoelectric properties of polycrystalline CuCrS2-xSex (x = 0, 0.5, 1.0, 1.5, 2) samples by replacing chalcogens and sintering

The optimization of thermoelectric properties of the CuCrS2-xSex (x = 0, 0.5, 1.0, 1.5, 2) samples was achieved by substitution in anionic sublattice and sintering at high temperature. The maximum power factor PF ~ 0.3 mW/m•K^2 among a series of samples with chalcogen substitution was obtained for CuCrS0.5Se1.5 sample at T=300 K. The sintering made it possible to obtain the maximum value PF ~ 2.1 mW/m•K2 for CuCrSe2 sample. This is due to a more than threefold increase in the thermoelectric power S(T) in CuCrSe2 sample with a spin-orbital interaction in comparison with CuCrS0.5Se1.5 sample with the same optimal electrical conductivity σ (σ300K ~ 100 S/cm), but without spin-orbital interaction. In CuCrSe2 sample, sintering effectively reduced the s to an optimal value, suppressed of the magnetic phase transition in the range of 50-100 K, and the weak localization were replaced by weak antilocalization indicating the appearance of strong spin-orbit interaction below 20 K. As a result, an additional contribution to the S(T) appeared due to the filtration of current carriers caused by the strong spin-orbit interaction. The effect of grain boundaries on the properties σ(T) and S(T) of the samples was investigated. It was established that polycrystalline samples with a high sulfur content were low-conductivity materials consisting of high-conductivity crystallites with the charge carriers concentration n ~ 1020 cm-3 separated by low-conductivity grain boundaries with fluctuation-induced tunneling conductivity. Both the replacement of sulfur with selenium and sintering led to a decrease in the energy barriers connecting grain boundaries. Selenium-dominated samples (CuCrS0.5Se1.5 and CuCrSe2) had high electrical conductivity with negligible energy barriers between grain boundaries. Logarithmic quantum corrections to the electrical conductivity was observed below 20 K, which indicated a quasi-two-dimensional electron transport in these samples.

Irreversible Thermodynamics at Surfaces: Inverse Edelstein Effect for Topological Insulator

We employ Onsager’s irreversible thermodynamics (IrTh) to study the Inverse Edelstein effect (IEE) for a non-magnetic material (NM) adjacent to a topological insulator (TI) with a strong spin-orbit interaction. The TI surface state region is treated as quasi two-dimensional (2d). For the IEE, the source is a 3d spin flux incident from the NM that converts, at the NM/TI interface, to a quasi-2d charge current in the TI. For the Edelstein Effect (EE), the source is a quasi-2d charge flux incident from the TI that converts, at the interface, to a three-dimensional (3d) spin flux in the NM. For strong spin-orbit coupling, as considered here, when the 3d spin flux crosses to the 2d TI, the quasi-2d charge current is produced along with a quasi-2d spin accumulation. (For weak spin-orbit coupling, production of charge current and of spin accumulation are distinct processes.) We compute the associated rates of heating.

Searching strong ‘spin’-orbit coupled one-dimensional hole gas in strong magnetic fields

We show that a strong `spin'-orbit coupled one-dimensional (1D) hole gas is achievable via applying a strong magnetic field to the original two-fold degenerate (spin degeneracy) hole gas confined in a cylindrical Ge nanowire. Both strong longitudinal and strong transverse magnetic fields are feasible to achieve this goal. Based on quasi-degenerate perturbation calculations, we show the induced low-energy subband dispersion of the hole gas can be written as $E=\hbar^{2}k^{2}_{z}/(2m^{*}_{h})+\alpha\sigma^{z}k_{z}+g^{*}_{h}\mu_{B}B\sigma^{x}/2$, a form exactly the same as that of the electron gas in the conduction band. Here the Pauli matrices $\sigma^{z,x}$ represent a pseudo spin (or `spin' ), because the real spin degree of freedom has been split off from the subband dispersions by the strong magnetic field. Also, for a moderate nanowire radius $R=10$ nm, the induced effective hole mass $m^{*}_{h}$ ($0.065\sim0.08~m_{e}$) and the `spin'-orbit coupling $\alpha$ ($0.35\sim0.8$ eV~\AA) have a small magnetic field dependence in the studied magnetic field interval $1<B<15$ T, while the effective $g$-factor $g^{*}_{h}$ of the hole `spin' only has a small magnetic field dependence in the large field region.