Low- and zero-energy quasiparticle heat transport in high-Tc superconductors Original Research Article

A review of our recent measurements on subkelvin thermal conductivity in single crystals of high-Tc cuprates is presented. At optimal doping, both Bi2Sr2CaCu2O8 and YBa2Cu3O7 exhibit a finite linear term in the temperature-dependence of their thermal conductivity. Moreover, in the former compound the size of the linear term does not change after the introduction of disorder by electron irradiation. Both these observations are in agreement with the standard theory of heat transport by nodal quasiparticles in d-wave superconductors. Surprisingly in the two underdoped systems studied here, the linear term is either too small (La1−xSRxCuO4, x=0.8) or absent (YBa2Cu4O8). The results point out the limits of our current theoretical understanding of transport by low-energy quasiparticles in the underdoped regime.