The quasiparticle DOS in the vortex state of YBa2Cu3O7 inferred from specific heat measurements

The specific heat C(B,T) of an YBa2Cu3O7.00 single crystal is measured from 1.2 to 10 K in magnetic fields up to 14 T. The anisotropic component C-ani so(T, B) = C(T, B parallel to c) - C(T, B perpendicular to c) is a pure vor tex quantity. Our data suggest that the electronic density of state (DOS) d ue to the vortices peaks at E = E-F, a very unusual behaviour. This result, necessary for thermodynamic considerations, agrees with a recent d-wave ca lculation. Moreover, this model predicts a scaling relation that is followe d by our data. Our experimental range corresponds to a crossover region whe re the limit C-aniso(T,B) proportional to TB1/2 used in former works does n ot strictly apply. (C) 1998 Elsevier Science Ltd. All rights reserved.