Spin Hall effect and Berry phase in two dimensional electron gas

The spin Hall effect is investigated in a high mobility two dimensional electron system with the spin-orbital coupling of both the Rashba and the Dresselhaus types. A spin current perpendicular to the electric field is generated by either the Rashba or the Dresselhaus coupling. The spin Hall conductance is independent of the stength of the coupling, but its sign is determined by the relative ratio of the two couplings. The direction of spin current is controllable by tuning the magnitude of the surface electric field perpendicular to the two dimensional plane via adjusting the Rashba coupling. It is observed that the spin Hall conductance has a close relation to the Berry phase of conduction electrons.Comment: 4 paper, 1 figure

Childhood Health Status and Adulthood Cardiovascular Disease Morbidity in Rural China: Are They Related?

Cardiovascular diseases (CVDs) are among the top health problems of the Chinese population. Although mounting evidence suggests that early childhood health status has an enduring effect on late life chronic morbidity, no study so far has analyzed the issue in China. Using nationally representative data from the 2013 China Health and Retirement Longitudinal Study (CHARLS), a Probit model and Two-Stage Residual Inclusion estimation estimator were applied to analyze the relationship between childhood health status and adulthood cardiovascular disease in rural China. Good childhood health was associated with reduced risk of adult CVDs. Given the long-term effects of childhood health on adulthood health later on, health policy and programs to improve the health status and well-being of Chinese populations over the entire life cycle, especially in persons’ early life, are expected to be effective and successful

Spin transverse force and quantum transverse transport

We present a brief review on spin transverse force, which exerts on the spin as the electron is moving in an electric field. This force, analogue to the Lorentz force on electron charge, is perpendicular to the electric field and spin current carried by the electron. The force stems from the spin-orbit coupling of electrons as a relativistic quantum effect, and could be used to understand the Zitterbewegung of electron wave packet and the quantum transverse transport of electron in a heuristic way.Comment: 4 pages, manuscript of invited talk on IAS Workshop on Spintronics at Nanyang Techological University, Singapore, 200

Topological superconducting states in monolayer FeSe/SrTiO3_{3}

The monolayer FeSe with a thickness of one unit cell grown on a single-crystal SrTiO$_{3}$ substrate (FeSe/STO) exhibits striking high-temperature superconductivity with transition temperature $T_{c}$ over 65K reported by recent experimental measurements. In this work, through analyzing the distinctive electronic structure, and providing systematic classification of the pairing symmetry , we find that both $s$-and $p$-wave pairing with odd parity give rise to topological superconducting states in monolayer FeSe, and the exotic properties of $s$-wave topological superconducting states have close relations with the unique non-symmorphic lattice structure which induces the orbital-momentum locking. Our results indicate that the monolayer FeSe could be in the topological nontrivial $s$-wave superconducting states if the relevant effective pairing interactions are dominant in comparison with other candidates.Comment: 11 pages, 4 figure

Topological phase in one-dimensional interacting fermion system

We study a one-dimensional interacting topological model by means of exact diagonalization method. The topological properties are firstly examined with the existence of the edge states at half-filling. We find that the topological phases are not only robust to small repulsive interactions but also are stabilized by small attractive interactions, and also finite repulsive interaction can drive a topological non-trivial phase into a trivial one while the attractive interaction can drive a trivial phase into a non-trivial one. Next we calculate the Berry phase and parity of the bulk system and find that they are equivalent in characterizing the topological phases. With them we obtain the critical interaction strengths and construct part of the phase diagram in the parameters space. Finally we discuss the effective Hamiltonian at large-U limit and provide additional understanding of the numerical results. Our these results could be realized experimentally using cold atoms trapped in the 1D optical lattice.Comment: 7 pages, 5 figures; revised version, references added, Accepted for publication in Physical Review

Finite-temperature conductivity and magnetoconductivity of topological insulators

The electronic transport experiments on topological insulators exhibit a dilemma. A negative cusp in magnetoconductivity is widely believed as a quantum transport signature of the topological surface states, which are immune from localization and exhibit the weak antilocalization. However, the measured conductivity drops logarithmically when lowering temperature, showing a typical feature of the weak localization as in ordinary disordered metals. Here, we present a conductivity formula for massless and massive Dirac fermions as a function of magnetic field and temperature, by taking into account the electron-electron interaction and quantum interference simultaneously. The formula reconciles the dilemma by explicitly clarifying that the temperature dependence of the conductivity is dominated by the interaction while the magnetoconductivity is mainly contributed by the quantum interference. The theory paves the road to quantitatively study the transport in topological insulators and other two-dimensional Dirac-like systems, such as graphene, transition metal dichalcogenides, and silicene.Comment: 5 pages, 5 figure

Optimal regularity of minimal graphs in the hyperbolic space

We discuss the global regularity of solutions $f$ to the Dirichlet problem for minimal graphs in the hyperbolic space when the boundary of the domain $\Omega\subset\mathbb R^n$ has a nonnegative mean curvature and prove an optimal regularity $f\in C^{\frac{1}{n+1}}(\bar{\Omega})$. We can improve the H\"older exponent for $f$ if certain combinations of principal curvatures of the boundary do not vanish, a phenomenon observed by F.-H. Lin.Comment: Accepted by Calc. Var. Partial Differential Equation

Double quantum dot as detector of spin bias

It was proposed that a double quantum dot can be used to be a detector of spin bias. Electron transport through a double quantum dot is investigated theoretically when a pure spin bias is applied on two conducting leads contacted to the quantum dot. It is found that the spin polarization in the left and right dots may be induced spontaneously while the intra-dot levels are located within the spin bias window and breaks the left-right symmetry of the two quantum dots. As a result, a large current emerges. For an open external circuit an charge bias instead of a charge current will be induced in equilibrium, which is believed to be measurable according to the current nanotechnology. This method may provide a practical and whole electrical approach to detect the spin bias (or the spin current) by measuring the charge bias or current in a double quantum dot.Comment: 13 pages, 5 figure