Low temperature specific heat of slightly overdoped YBa2Cu3O7−δ

Specific heat of a slightly overdoped YBa2Cu3O7−δ single crystal has been measured at magnetic fields up to 12 T in low temperature region. By subtracting a spare linear term (γ0T), the phonon contribution (βT3 + ηT5) and the Schottky anomaly (CSch), we obtain the field induced change of the specific heat coefficient Δγ which behaves as the AH dependence (A is a constant) in zero-temperature limit and satisfies the Simon-Lee scaling law at finite temperatures, as expected by pure d-wave theory. The upper critical field Hc2(0) is then determined according to the expression of A=0.74γn/Hc2(0) in the framework of d-wave theory. This may be an alternative way to derive the Hc2(0) value.