Link between superconductivity and a Lifshitz transition in intercalated Bi2Se3

Abstract

Topological superconductivity is an exotic phase of matter in which the fully gapped superconducting bulk hosts gapless Majorana surface states protected by topology. Intercalation of copper, strontium, or niobium between the quintuple layers of the topological insulator Bi 2 Se 3 increases the carrier density and leads to superconductivity that is suggested to be topological. Here we study the electronic structure of strontium-intercalated Bi 2 Se 3 using angle-resolved photoemission spectroscopy and Shubnikov-de Haas oscillations. Despite the apparent low Hall number of ∼2 × 10 19 cm −3 , we show that the Fermi surface has the shape of an open cylinder with a larger carrier density of ∼10 20 cm −3 . We suggest that superconductivity in intercalated Bi 2 Se 3 emerges with the appearance of a quasi-two-dimensional open Fermi surface.

Lifshitz transition in dirty nematic superconductor

“…Lifshitz transition appears in topological insulator Bi 2 Se 3 upon doping with Nb or Cu [38,39]. The appearance of this transition coincides with the emergence of superconductivity in the system [39].…”

“…In Ref. [39] the authors state that the superconductivity in doped topological insulators appears along with the Lifshitz transition from closed to open Fermi surface. Open Fermi surface has been observed in different compounds of doped topological insulators with the nematic superconductivity [38,50,51].…”

“…This transition occurs in underdoped cuprates and has a significant effect on the superconducting properties [35][36][37]. Lifshitz transition appears in topological insulator Bi 2 Se 3 upon doping with Nb or Cu [38,39]. The appearance of this transition coincides with the emergence of superconductivity in the system [39].…”

Pauli paramagnetism of triplet Cooper pairs in a nematic superconductor

“…Angle-resolved photoemission spectroscopy and measurements of Shubnikov-de Haas oscillations show that the Fermi surface in doped Bi 2 Se 3 is open in ΓZdirection [31,32]. An increase of the chemical potential by doping transforms the closed ellipsoid Fermi surface of undoped samples to a corrugated cylinder Fermi surface of doped samples.…”

“…Theoretical calculations predict the chiral phase is the ground state in 2D films of doped Bi 2 Se 3 [26,27] while in a 3D system with a closed Fermi surface, the nematic phase has the lower free energy than the chiral state [28][29][30]. Experimentally, the Fermi surface of doped Bi 2 Se 3 with the superconductivity has a topology of an open cylinder [31,32] which is an intermediate case between 2D and 3D Fermi surface. This transition to the open Fermi surface leads to the phase transition from nematic to chiral phase [33].…”