Multiple Fermi surfaces in superconducting Nb-dopedBi2Se3

Abstract

Topological insulator Bi2Se3 has shown a number of interesting physical properties. Doping Bi2Se3 with copper (Cu) or strontium (Sr) has been demonstrated to make the material superconducting and potentially even a topological superconductor. The recent discovery of superconducting niobium (Nb) doped Bi2Se3 reveals an exciting new physical phenomenon, the coexistence of superconductivity and magnetic ordering, as well as signatures of an odd-parity p-wave superconducting order. To understand this new phenomenon, a detailed knowledge of the electronic structure is needed. To date, the quantum oscillations needed to reveal this structure have not been reported in Nb-doped Bi2Se3. In this rapid communication, we present the first observation of quantum oscillations in the magnetization (the de Haas-van Alphen effect) of Nb-doped Bi2Se3. In the fully superconducting crystal, two distinct orbits are observed, in sharp contrast to Bi2Se3, Cu-doped Bi2Se3, and Sr-doped Bi2Se3. The multiple frequencies observed in our quantum oscillations, combined with our electrical transport studies, indicate the multi-orbit nature of the electronic state of Nb-doped Bi2Se3.

An increase in T under hydrostatic pressure in the superconducting doped topological insulator Nb0.25Bi2Se3

“…Here, m * , v F , e, ρ and n are the effective mass, Fermi velocity, electron charge, resistivity, and carrier concentration, respectively. Using m * = 0.15 and v F = 7x10 5 m/sec from dHvA measurements (average values from [33]), ρ 0 = 0.25x10 −4 Ω*cm from Fig. 1, and n = 1.5x10 20 cm −3 from Hall measurements [13,33], we obtain l ∼ 50 nm.…”

“…The material is metallic with a residual resistivity ratio R 250K /R 4K ∼ 6 and a fairly low residual resistivity, ρ 0 ∼ 0.25 mΩ * cm. The observation of quantum oscillations in similar crystals [33] is taken as evidence of the high purity of this material. Using a single-band Drude model, the electron mean free path l is given as l = m * v F /(ne 2 ρ).…”

Superconducting and normal-state anisotropy of the doped topological insulator Sr0.1Bi2Se3

“…6. Furthermore, quantum oscillation measurements [39][40][41] on the Nb and Cu homologues suggest that the planar cross-section of the Fermi surface shows little warping, indicating that effective mass anisotropy cannot be the sole cause of the anisotropy in H c2 .…”

Evidence of nodes in the order parameter of the superconducting doped topological insulator NbxBi2Se3 via penetration depth measurements

“…For instance, impurity scattering can alter the linear T-dependence characteristic of line nodes to a quadratic variation as has been discussed for a variety of materials 43,[51][52][53][54][55] . We do not believe that our samples are in the dirty limit since the observation of quantum oscillations in the Cu-homologue 56,57 and more recently in the Nb-compound 46 suggests that these materials have in fact fairly high purity.…”