Evidence of d-wave pairing in MTG-YBa_2Cu_(2.99)Li_(0.01)O_x crystals determined from the low-temperature specific heat

摘要

The specific heat of a melted-textured-growth (MTG) YBa_2Cu_(2.99)Li_(0.01)O_x. crystal has been measured from 1.8 to 30 K in different fields up to 9 T parallel to the c-axis by the thermal relaxation technique. The defects induced by Li-doping and the paramagnetic centres have a strong effect on the low-temperature specific heat. The electronic specific heat C_e(T, H)/T at lower temperatures (T < 5 K) follows alpha T at 0 T and AH~(1/2) in the magnetic field, and can be scaled on a line, C_e(T, H)/TH~(1/2) = F(T/H~(1/2)). These results are consistent with that of the d-wave superconductor predicted theoretically by Volovik, indicating that a Li-doped MTG-Ba_2Cu_(2.99)Li_(0.01)O_x crystal should be a d-wave superconductor.