Superconducting properties and gap structure of the topological superconductor candidate Ti_(3)Sb

TL;DR

This study characterizes the superconducting and gap properties of Ti_3Sb, a candidate topological superconductor, revealing conventional s-wave pairing with extreme type-II behavior and modest coupling.

Contribution

It provides detailed measurements of superconducting parameters and confirms a full s-wave gap structure in Ti_3Sb, advancing understanding of its topological superconductor potential.

Findings

Superconducting transition temperature T_c,onset ~ 5.9 K

Full superconducting gap consistent with s-wave pairing

Extreme type-II superconductor with GL parameter ~55

Abstract

We present a study of the superconducting properties of the candidate topological superconductor Ti_(3)Sb. Electrical transport measurements show zero resistance with a T_(c,onset) of ~ 5.9 K with a transition width {\Delta}T_c~ 0.6 K. The superconducting phase boundaries as derived from magneto-transport and magnetic susceptibility measurements agree well. We estimate an upper critical field Bc2(0)~4.5 T. A Ginzburg-Landau (GL) analysis yields values of the coherence length and penetration depth of {\zeta} = 6.2 nm and {\lambda} = 340 nm, respectively, and a GL parameter ~ 55, indicating extreme type-II behavior. Furthermore, we observed a step height in the specific heat ({\Delta}C_e)/({\gamma}T_c )~1.61, a value larger than the Bardeen-Cooper-Schrieffer (BCS) value of 1.43, suggesting modest coupling. Measurements of the temperature dependence of the London penetration depth via the tunnel-diode oscillator (TDO) technique down to ~ 450 mK show a full superconducting gap, consistent with a conventional s-wave gap structure.