Condensed Matter Physics Seminar

Scaling laws in high-temperature superconductors

Dr. C.C. Homes
Department of Physics, Brookhaven National Laboratory
Tuesday, November 16, 2004
Higgins 235, 2pm

Superconductivity at elevated temperatures in the copper-oxide materials has proven to be one of the great challenges in condensed matter physics. Despite 18 years of intensive study, the nature of the superconductivity in these systems is still not agreed upon. Scaling laws express a systematic and universal simplicity among complex systems in nature. We have recently observed a linear scaling relation in the high-temperature superconductors between the strength of the superconducting condensate (a measure of the number of carriers in the superconducting state), the critical temperature, and the dc conductivity just above the critical temperature – this scaling relation does not depend on the crystal structure, type of dopant, nature of the disorder, or direction. Interestingly, values for the elemental superconductors Nb and Pb also fall on this line. However, it may be shown from spectral weight arguments that these points correspond to systems in the BCS “dirty” limit (the scattering rate is much larger than the energy gap). The scaling relation for the copper-oxide materials will be addressed within the context of the “clean” and “dirty” limits, and the implications of each approach discussed.