Spin-triplet vortex state in the topological superconductor CuxBi2Se

Abstract

We report on the observation of bulk superconductivity from dc magnetization measurements in a cylindrical single crystal of Cu x Bi 2 Se 3 . The magnitude of the magnetization in the Meissner state is very small, and the magnetic-field dependence of the magnetization just above the lower critical field H c1 is very different from those of usual type-II superconductors. We studied the character of the vortex state theoretically in a spin-triplet pairing superconductor and compared it with the experimental results. The results showed that the superconductivity observed in Cu x Bi 2 Se 3 is consistent with the spin-triplet pairing superconductivity with odd parity. We also observed a rapid relaxation phenomenon of the superconducting diamagnetism.

Vortex state of topological superconductorCuxBi2Se3

“…The magnetization increases in the small region of magnetic field around H 0 c1 . This behavior is the same as that of the magnetization curve observed in the experiments with use of the superconducting single crystal of Cu 0.15 Bi 2 Se 3 [6]. Since our theory assumes that the vortex density is small and only takes into account the vortex-vortex interaction of the nearest neighbors, it is only adequate in the vicinity of H c1 .…”

“…λ is taken from the value obtained in the earlier experiment, λ = 7 × 10 −5 cm (ξ ab = 14 nm, κ = 50 [2]); the volume fraction of the superconducting domains is estimated to be 0.025/5 = 5 × 10 −3 using the value of 4πM = −0.025 gauss at H c1 = 5 Oe observed in the experiment [6]. The magnetization curve is shown in Fig.…”

“…Using the vortex density n and the formula experiment by Das et al [6], we take H 0 c1 = 5 Oe from the H c1 value observed in the experiment. λ is taken from the value obtained in the earlier experiment, λ = 7 × 10 −5 cm (ξ ab = 14 nm, κ = 50 [2]); the volume fraction of the superconducting domains is estimated to be 0.025/5 = 5 × 10 −3 using the value of 4πM = −0.025 gauss at H c1 = 5 Oe observed in the experiment [6].…”

“…Das et al made the cylindrical-shaped single crystal (diameter 6 mm and height 1 mm) of Cu 0.15 Bi 2 Se 3 [6]. The superconducting transitions of the sample occurs at the temperature of 3.6 K [6].…”

“…The superconducting transitions of the sample occurs at the temperature of 3.6 K [6]. They measured the DC magnetization of the crystal with the use of a SQUID magnetometer (Quantum Design Inc., USA).…”