Phonon scattering in HTSC cuprate crystals

From results of measurements of thermal conductivity (kappa(ab) and kappa(c )) and electric resistivity (rho(ab) and rho(c)) of the HTSC YBa2Cu3O7-x an d Bi2Sr2CaCu2O8+y single crystals, made on the same samples with transition temperatures T-c close to 90 K, we have estimated that above T-c the phono n contribution kappa(p) to the total thermal conductivity in the db-plane k appa(ab) can be comparable or higher than the electronic contribution kappa (e) in Y-crystals, though in all studied Bi-crystals kappa(p) much greater than kappa(e). In the superconducting state the relative height of the maxi ma on the kappa(ab)(T)/kappa(ab)(T-c) curves in both Y- and Bicrystals can reach 2, and the maximum position is shifted toward low temperatures T-m si milar to 0.4 T, with this ratio increasing in contrast to predictions of th e theories of electronic heat transport in anisotropic HTSC cuprates. Takin g into account the estimations of the electronic contributions kappa(e)(T) from the known experimental behaviour of conductivity of the normal carrier s below T-c and recent observations of the thermal Hall conductivity in Y-c rystals in the mixed state we can conclude that: (a) the nature of the obse rved maxima should be attributed to the increase in both the phonon re, and electron h-e contributions below T-c, and (b) in perfect HTSC crystals the mean free paths of phonons l(p) and normal electron excitations l(e), rest ricted at T similar to T-c by the mutual phonon-carrier scattering, should grow quickly the temperature is lowered below T-c to overcome the decrease of the appropriate heat capacity terms C-p and C-e. In the c-direction kapp a(p) much less than kappa(e) in all the samples, and the total thermal cond uctivity kappa(c)(T) decreases monotonously at temperatures 200-7 K. In add ition to the strong anisotropy of the layered cuprate crystals one should t ake into account the scattering of phonons by interlayer defects and the sa mple boundaries when discussing the kappa(c)(T) dependence. (C) 1999 Elsevi er Science B.V. All rights reserved.