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Anisotropic Upper Critical Field, Seebeck and Nernst Coefficient in Nb0.20Bi2Se3 Topological Superconductor

We present the magneto-transport and the thermoelectric (Seebeck and Nernst coefficient) studies of the Nb-doped Bi2Se3 topological superconductor. The angle-dependent magnetoresistance study highlights the anisotropy in the upper critical field (Hc2) with the anisotropy parameter Gamma ~1.2. We observed a gradual decrease in low-temperature Hall resistivity on the application of magnetic field like any conventional superconductor, instead of the finite Hall resistivity which was linked to the chiral superconducting phase. The estimated value of the carrier concentration (~ 10^19 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 micro V K-1 T-1) of Nernst coefficient for Bi2Se3 at room temperature which decreases with Nb doping ( ~0.5 micro V K-1 T-1).