Unusual magnetic-field dependence of the electrothermal conductivity in the mixed state of cuprate superconductors.

Abstract

In the mixed state of a superconductor, the electrothermal conductivity, P, which measures the electrical current density produced by a thermal gradient, is supposed to be independent of both the magnetic field and the details of the vortex motion. Measurements of the thermopower and resistivity in ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$, ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{8+\mathrm{\ensuremath{\delta}}}$, and ${\mathrm{Tl}}_{2}$${\mathrm{Ba}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{8+\mathrm{\ensuremath{\delta}}}$ show an unusual, sharp structure in P at low field. In ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{8+\mathrm{\ensuremath{\delta}}}$, the extra contribution is negative, causing a sign change of the thermopower versus applied magnetic field. The possible origins of the low-field anomaly are discussed. \textcopyright{} 1996 The American Physical Society.