Theoretical Analysis On The Properties Of Two-band Degenerate-gaps Superconductor S_rPt₃P

Since the discovery of superconductivity at 39 K in magnesium diboride,extensive efforts have been devoted to understanding the superconducting mechanism and physical properties of this compound.The electronic structure of MgB₂ is now rather well known and the superconductivity is ascribed to the conventional electron-phonon mechanism.The Fermi surface of this compound consists of two three-dimensional sheets from thep-band,and two nearly cylindrical sheets from the two-dimensional s-band.The qualitative difference between these two bands suggests a multi-band description of the superconductivity in MgB₂.Thereafter,this two-gap picture was clearly confirmed by specific heat measurements,scanning tunneling microscopy,Raman spectrum and other experiments.We study the magnetic properties of two-band degenerate-gaps superconductor S_rPt₃P with two-band isotropic Ginzburg–Landau theory.The exact solutions of upper critical field and London penetration depth are obtained,and the calculations reproduce the experimental data of S_rPt₃P in a broad temperature range.It directly underlies that S_rPt₃P is a multi-band superconductor with equal gaps in two Fermi surface sheets.After that,we use the similar methods to analyze the upper critical filed and London penetration depth of non-centrosymmetric superconductor LaNiC₂,and the upper critical filed of centrosymmetric superconductor Cs Ni₂Se₂.The calculations fit the experimental data very well.Thus our results show strong evidence that two-gap scenario is better to account for the superconductivity of LaNiC₂ and CsNi₂Se₂.