Low-temperature specific heat of single-crystal YBa2Cu3O7−δ

Abstract

The low-temperature specific heat has been measured on both orthorhombic (superconducting) and tetragonal single crystals of ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$. The Debye temperature extracted from the $T^3$ term decreases with increasing oxygen vacancy concentration consistent with glassy behavior in disordered solids. A linear γT term, however, exists for both phases. It is proposed that this term is at least in part electronic, even in the superconducting state, and is due to extended or localized states at the Fermi energy.