Anisotropic upper critical field, Seebeck and Nernst coefficient of Nb0.20Bi2Se3 superconductor

Abstract

Abstract We present the magneto-transport and the thermoelectric (Seebeck and Nernst coefficient) studies of the Nb-doped Bi2Se3 superconductor. The angle-dependent magnetoresistance study highlights the anisotropy of upper critical field (Hc 2) for in-plane and out-of-plane magnetic field orientation with the anisotropy parameter Γ ∼ 1.3. The estimated value of the carrier concentration (∼1019 cm−3) for Nb0.2Bi2Se3 is one order larger than for Bi2Se3. Doping of Nb shows a significant decrease in the Seebeck coefficient value and the estimated Fermi temperature of the three-dimensional Fermi surface at the centre of Brillouin zone in the zero-temperature limit enhances by ∼4 times in comparison to pristine Bi2Se3. We have observed a large value (∼2.3 µV K−1T−1) of Nernst coefficient for Bi2Se3 at room temperature, which decreases with Nb doping (∼0.5 µV K−1 T−1).