Low temperature specific heat studies on the pairing states of high-Tc superconductors:: a brief review

Low temperature specific heat (LTSH) data on a variety of high-T-c superconductors, such as YBa2Cu3O7, La1-xSrxCuO4, Bi2Sr2CaCu2O8, and Ba0.6K0.4BiO3 are reviewed. The agreement between the experimental data and theoretical predictions, such as T-2-dependence of specific heat at zero magnetic field and H-1/2-dependence of electronic specific heat is widely discussed within the scenario of d-wave superconductivity. Impurity scattering effects and scaling model on d-wave superconductivity are verified using Zn- and Ni-doped La1-xSrxCuO4. The low energy quasiparticle density of states N(E) = N(0) + E-1/2 are deduced from dirty d-wave superconductors. Absence of paramagnetic contribution to LTSH is found both in superconducting and nonsuperconducting underdoped samples suggesting that a mechanism beyond Kondo screening model maybe required to explain its magnetic property. (C) 2001 Elsevier Science Ltd. All rights reserved.