We theoretically study the electronic transport through a ferromagnet-Ising superconductor junction. A tight-binding Hamiltonian describing the Ising superconductor is presented. Then by combing the non-equilibrium Green's function method, the expressions of Andreev reflection coefficient and conductance are obtained. A strong magnetoanisotropic spin-triplet Andreev reflection is shown, and the magnetoanisotropic period is π instead of 2π as in the conventional magnetoanisotropic system. We demonstrate a significant increase of the spin-triplet Andreev reflection for the single-band Ising superconductor. Furthermore, the dependence of the Andreev reflection on the incident energy and incident angle are also investigated. A complete Andreev reflection can occur when the incident energy is equal to the superconductor gap, regardless of the Fermi energy (spin polarization) of the ferromagnet. For the suitable oblique incidence, the spin-triplet Andreev reflection can be strongly enhanced. In addition, the conductance spectroscopies of both zero bias and finite bias are studied, and the influence of gate voltage, exchange energy, and spin-orbit coupling on the conductance spectroscopy are discussed in detail. The conductance reveals a strong magnetoanisotropy with period π as the Andreev reflection coefficient. When the magnetization direction is parallel to the junction plane, a large conductance peak always emerges at the superconductor gap. This work offers a comprehensive and systematic study of the spin-triplet Andreev reflection, and has underlying application of π-periodic spin valve in spintronics.PACS numbers:
The thermoelectric properties of the surface states in three-dimensional topological insulator nanowires are studied. The Seebeck coefficients Sc and the dimensionless thermoelectrical figure of merit ZT are obtained by using the tight-binding Hamiltonian combining with the nonequilibrium Green's function method. They are strongly dependent on the gate voltage and the longitudinal and perpendicular magnetic fields. By changing the gate voltage or magnetic fields, the values of Sc and ZT can be easily controlled. At the zero magnetic fields and zero gate voltage, or at the large perpendicular magnetic field and nonzero gate voltage, ZT has the large value. Owing to the electron-hole symmetry, Sc is an odd function of the Fermi energy while ZT is an even function regardless of the magnetic fields. Sc and ZT show peaks when the quantized transmission coefficient jumps from one plateau to another. The highest peak appears while the Fermi energy is near the Dirac point. At the zero perpendicular magnetic field and zero gate voltage, the height of nth peak of SC is k B e ln2/(|n| + 1/2) and k B e ln2/|n| for the longitudinal magnetic flux φ = 0 and π, respectively. Finally, we also study the effect of disorder and find that Sc and ZT are robust against disorder. In particular, the large value of ZT can survive even if at the strong disorder. These characteristics (that ZT has the large value, is easily regulated, and is robust against the disorder) are very beneficial for the application of the thermoelectricity.PACS numbers:
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