Specific heat of high temperature superconductors in high magnetic fields

Abstract

We review investigations of the mixed-state specific heat (C) of extreme type-II superconductors in magnetic fields B≤16 T, from 1 K to T c. In YBa 2Cu 3O x (Y123) at low temperature T, a scaling law Δ C∞( TB 1 2 )ƒ( T/B 1 2 ) , which is a signature of d-wave symmetry, is observed for the background-free anisotropic component ΔCC(B//c)-C(B//ab). At intermediate T, a C(B)C(0)∞T nBlnB behaviour, which may be explained by the London model, smoothly sets in. Near T c, superconducting fluctuations are investigated using the background-free derivative ∂(C/T)/∂B. 3D-XY scaling properties are verified up to the overdoped regime. Fluctuations obey different laws in Bi 2Sr 2CaCu 2O x (Bi2212), which is strongly affected by its 2D character. Finally, the melting line of the vortex solid, which is now believed to be the only true phase transition above H c1 in the presence of fluctuations, is observed in Y123 either as a 1st- or 2nd-order transition, depending on pinning.