Upper critical magnetic field in superconducting Dirac semimetal

Abstract

Temperature dependence of the upper critical field H-c2 of the Dirac semimetal (DSM) with phonon-mediated pairing is considered within the semiclassical approximation. The low-temperature dependence deviates from conventional BCS superconductor with parabolic dispersion relation (WERTHAMER N. R., HELFAND E. and HOHENBERG P. C., Phys. Rev., 147 (1966) 295; HELFAND E. and WERTHAMER N. R., Phys. Rev. Lett., 13 (1964) 686) even for large adiabaticity parameter, gamma = mu/(sic)Omega), where mu is the chemical potential and Omega the Debye frequency. In particular the "reduced field", ratio of zero-temperature H (c2) to the derivative at critical temperature, h* = H (c2)(0)/(-T dH(c2)/dT)vertical bar T-c, depends on gamma and can be extended beyond the adiabatic limit. The reduced magnetic field ratio is universal (independent of the chemical potential, interaction strength, etc.) and smaller than the Werthamer ratio for clean superconductors: h* = 0.55 for DSM, h* (0) = 0.69 for parabolic band. The results are in good agreement compared with recent experiments on TaP. Copyright (C) EPLA, 2018