Evolution of the Fermi surface of a doped topological insulator with carrier concentration

Abstract

In an ideal bulk topological insulator (TI) conducting surface states protected by time-reversal symmetry enfold an insulating crystal. However, the archetypical TI, Bi 2 Se 3 , is actually never insulating; it is in fact a relatively good metal. Nevertheless, it is the most studied system among all the TIs, mainly due to its simple band structure and large spin-orbit gap. Recently, it was shown that copper intercalated Bi 2 Se 3 becomes superconducting and it was suggested as a realization of a topological superconductor. Here we use a combination of techniques that are sensitive to the shape of the Fermi surface (FS): the Shubnikov-de Haas effect and angle-resolved photoemission spectroscopy to study the evolution of the FS shape with carrier concentration, n. We find that as n increases, the FS becomes two-dimensional-like. These results are of crucial importance for understanding the superconducting properties of Cu x Bi 2 Se 3 .

Nematic superconductivity in CuxBi2Se3 : Surface Andreev bound states

“…A completely twodimensional model with zero hopping along the z direction is unsuitable because it cannot give the TSSs observed in experiments [2,28]. In addition, the relative magnitudes of the various parameters in Table I are in agreement with the set of parameters obtained previously by fitting the first-principle band structures for Bi 2 Se 3 [32,37].…”

“…After intercalating copper to interquintuple-layer positions, the material becomes more two-dimensional. According to the experiments [28], the Fermi surface for certain Cu x Bi 2 Se 3 becomes (corrugated) cylindrical, although the details of the evolution are still unclear. On the other hand, a common feature of the normal phase of superconducting Cu x Bi 2 Se 3 is that the TSSs are well defined and coexist with the Fermi surface [2,28].…”

Thermodynamic evidence for nematic superconductivity in CuxBi2Se3

“…We also performed calculations for a Q2D Fermi surface. We used a Q2D tight-binding model for the normal-state electronic band 17 and assumed a point-nodal gap 31 , as schematically shown in the inset of Supplementary Fig. 6c.…”

“…On the other hand, a scanning tunnelling microscopy (STM) experiment on the ab-plane revealed s-wave-like tunnelling spectra 15 , which was later actually found to be inconsistent with the s-wave (∆ 1 ) scenario 16 . Rather, it was proposed that the STM spectra may be explained within the topological superconductivity scenario by taking into account the possible quasi-two-dimensional (Q2D) nature of the Fermi surface 12,17 . More recently, by means of the nuclear-magnetic resonance (NMR), spin-rotational symmetry was revealed to be broken in the SC state 18 , suggesting realization of the ∆ 4x or ∆ 4y states.…”

Pressure-induced superconductivity in the three-dimensional topological Dirac semimetal Cd3As2

“…7,8 Under pressure, Bi 2 Te 3 , Bi 2 Se 3 , Sb 2 Te 3 and Sb 2 Se 3 become superconducting, which are also regarded as candidates for TSCs. [9][10][11][12][13][14] Note that there are debates on whether these candidates are indeed TSCs, [9][10][11][12][13][14][15][16][17] therefore further experimental works are needed to definitely identify a TSC and manipulate the Majorana fermions on its surface.…”