ORAL SESSION 2C3: Thermal Properties

Tuesday, Feb. 22, 3:30 p.m. – 6:00 p.m., Room 302A (GRB)

Chairs: D. Gubser (Naval Research Lab), J.L. Tholence (CNRS)

2C3.1 Specific Heat of YBa₂Cu₃O_7-d : Paramagnetic Centers; Evidence for d-Wave Pairing*

N.E. Phillips 1, R.A. Fisher 1, J.P. Emerson 1, J.E. Gordon 1,2, B.F. Woodfield 1,3, and D.A. Wright 1. 1 Lawrence Berkeley National Laboratory and Department of Chemistry, Berkeley, CA 94720, USA. 2 Department of Physics, Amherst College, Amherst, MA 01002, USA. 3 Department of Chemistry and Biochemistry, Brigham Young University, Provo, UT 84602, USA.

Presenting Author: N.E. Phillips

Low-temperature specific-heat data for YBa₂Cu₃O_7-d , 0 £ d £ 0.2, in magnetic fields to 9T are reported. They show the presence of both spin-1/2 and singlet-ground-state spin-2 paramagnetic centers, and features predicted for the lines of nodes in the energy gap that are expected for d-wave pairing.

*The work at LBNL was supported by the Director, Office of Basic Energy Sciences, Materials Sciences Division of the U. S. Department of Energy under Contract No. DE-AC03-76SF00098.

2C3.2 Low-Energy Quasiparticles in Cuprate Superconductors

Louis Taillefer 1, R.W. Hill 1, Christian Lupien 1, M. Sutherland 1, May Chiao 2, Robert Gagnon 2, P. Fournier 3, and R.L. Greene 3. 1 Canadian Institute for Advanced Research and Department of Physics, University of Toronto. 2 Department of Physics, McGill University. 3 Center for Superconductivity Research and Department of Physics, University of Maryland.

Presenting Author: L. Taillefer

In a d-wave superconductor, a residual linear term in the thermal conductivity at very low temperature is a direct quantitative measure of the quasiparticle spectrum at low energy, unaffected by either Fermi-liquid or vertex corrections. We present measurements of heat transport in three cuprate superconductors which shed light on the following issues: 1) the evolution of the d-wave spectrum with hole doping in YBCO, 2) the nature of impurity scattering in Bi-2212, 3) the symmetry of the order parameter in the elecron-doped compound PrCeCuO, and 4) Fermi-liquid corrections to the superfluid density in YBCO and Bi-2212.

2C3.3 Effect of controlled disorder onthermal conductivity of Bi2212

Kamran Behnia 1,Sawako Nakamae 1, FlorenceRullier-Albenque 2, and Tsuyoshi Tamegai 3. 1 UPR 5 (CNRS), Laboratoirede Physique Quantique, ESPCI , 10 Rue Vauquelin, 75005 Paris,France. 2 Laboratoire des Solides Irradiés (CEA), Ecole Polytechnique, 91128,Palaiseau, France. 3 Departmentof Applied Physics, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo,113-8656, Japan.

Presenting Author: K. Behnia

In-plane thermal conductivity of optimally-doped Bi2212 single crystals were studied before and after irradiation by high-energy electrons. Introduction of point defects by this procedure decreases the quasi-particle mean-free-path and weakens the superconductivity due to pair-breaking effects. The latter leads to a decline in the critical temperature and an enhancement of low-energy excitations. We discuss the results of the thermal conductivity data on a wide temperature range (100 mK to 100 K) in the light of our current theoretical understanding of transport properties of nodal quasi-particles.