HALL-EFFECT OF EPITAXIAL YBA2CU3O7-X AND BI2SR2CACU2OY FILMS - INTERPRETATION OF THE HALL-EFFECT ON THE BASIS OF A RENORMALIZED TIGHT-BINDING MODEL

The Hall effect of epitaxial YBa2Cu3O7-x (T(c) almost-equal-to 90 K) and Bi2Sr2CaCu2Oy (T(c) almost-equal-to 80 K) films has been investigated. In both compounds the Hall coefficient R(H) (B parallel-to c axis) in the normal phase is positive and exhibits a strong temperature dependence, which is more pronounced in YBa2Cu3O7-x than in Bi2Sr2CaCu2Oy. On the basis of a renormalized two-dimensional tight-binding band structure the normal-state Hall coefficient R(H) has been calculated as a function of doping concentration and temperature using the relaxation-time approximation. Strong correlation effects are considered to some extent via doping-dependent nearest- and next-nearest-neighbor hopping terms leading to band-narrowing effects. The consideration of the latter term strongly influences the Hall coefficient. The Hall effect has been explored for two quite different models: (i) doping creates holes close to the top of an effective oxygen band, which is located between the lower and the upper Hubbard band; (ii) doping creates holes in a less than half-filled antibonding CuO2 subband. The influence of the relaxation time tau(k) on the Hall coefficient has been explored by considering two simple choices, namely a k-independent tau0, and tau(k) = l(T, delta)/\v(k)\ (l is the mean free path and delta the doping concentration). Depending on the relaxation time different results have been obtained for the Hall coefficient. Assuming that holes are doped in the oxygen band and tau(k) is-proportional-to \v(k)\-1 a good agreement between theory and experimental data of Bi2Sr2CaCu2Oy has been achieved, whereas for YBa2Cu3O7-x the pronounced temperature dependence of R(H) is qualitatively reproduced. A comparison between the predictions of the Hall effect and the corresponding Fermi surfaces is made. We have also calculated some band parameters including the Drude plasma energy, the Fermi velocity, and the carrier effective mass.