Quantum oscillations inCuxBi2Se3in high magnetic fields

Abstract

CuxBi2Se3 has drawn much attention as the leading candidate to be the first topological superconductor and the realization of coveted Majorana particles in a condensed matter system. However, there has been increasing controversy about the nature of its superconducting phase. This study sheds light on ambiguity in the normal-state electronic state by providing a complete look at the quantum oscillations in magnetization in CuxBi2Se3 at high magnetic fields up to 31 T. Our study focuses on the angular dependence of the quantum oscillation pattern in a low carrier concentration. As the magnetic field tilts from the crystalline c-axis to the ab-plane, the change of the oscillation period follows the prediction of the ellipsoidal Fermi surface. As the doping level changes, the 3D Fermi surface becomes quasi-cylindrical at high carrier density. Such a transition is potentially a Lifshitz transition of the electronic state in CuxBi2Se3.

Bulk Fermi surface and electronic properties of Cu0.07Bi2Se3

“…Surprisingly, this value is nearly identical to those previously obtained on the undoped Bi 2 Se 3 [9,10]. Nevertheless, our result for 7% Cu doping seems to be in line with a recent report, where a very small enhancement (m * = 0.19m 0 ) was reported for the superconducting samples with x = 0.25, three times as much Cu as in our samples [11]. Therefore, while a large increase of m * may occur with Cu doping in some cases, it does not appear to be a general trend.…”

“…[8] and Ref. [11]. the critical temperature was very similar T c ≈ 3K, underlying the complex nature of doping in Bi 2 Se 3 .…”

“…The anisotropy is k c F /k ab F = 1.8, slightly larger than previous values of k c F /k ab F =1.2-1.6 obtained for Bi 2 Se 3 [9,10], making un-likely that anisotropy plays an important role in superconductivity. Moreover, anisotropy was found to decrease slightly for 25% Cu doping [11]. These results are rather relevant for the non-monotonic effect of Cu addition on the band structure of Bi 2 Se 3 .…”

“…The carrier concentration is n = 1/3π 2 k ab 2 F k c F ≈ 5×10 18 cm −3 , almost identical to the value we obtained from Hall coefficient. It is important to mention that larger carrier concentrations, up to about 2-3 ×10 19 cm −3 were reported in recent studies of undoped Bi 2 Se 3 [10,11] and that the superconducting samples of Cu x Bi 2 Se 3 seem to have n ≥ 5×10 19 cm −3 . Therefore, it is possible that there is a threshold carrier concentration required for superconductivity.…”

“…Heat capacity measurements [8] on superconducting Cu x Bi 2 Se 3 , with x = 0.29 and n = 1.3 × 10 20 cm −3 , found a manyfold enhancement of the electron effective mass, with m * = 2.6m 0 , compared to undoped Bi 2 Se 3 , where m * ≈ 0.14m 0 [9,10]. However, a much less significant increase, m * ≈ 0.2m 0 , was observed from quantum oscillations for similar doping level, x = 0.25 and n = 4.3 × 10 19 cm −3 [11]. In both Ref.…”