Low temperature specific heat of slightly overdoped YBa2Cu3O7-δ

Specific heat of a slightly overdoped YBa2Cu3O7-delta single crystal has been measured at magnetic fields up to 12 T in low temperature region. By subtracting a spare linear term (gamma T-0), the phonon contribution (beta T-3 + eta T-5) and the Schottky anomaly (C-Sch), we obtain the field induced change of the specific heat coefficient Delta gamma which behaves as the A root H 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 H-c2(0) is then determined according to the expression of A = 0.74(gamma n)/root H-c2(0) in the framework of d-wave theory. This may be all alternative way to derive the H-c2(0) value. (c) 2005 Elsevier B.V. All rights reserved.