FERMION-FERMION SCATTERING IN THE HALL-MOBILITY OF LA-214 HTSC

The inverse Hall mobility mu-1=rho/R(H) in (La2-xSrx)CuO4 follows a si mple temperature dependence mu-1 = a + b . T(m) in under- and overdope d samples (0.1 less-than-or-equal-to x less-than-or-equal-to 0.21). Th is relation holds even in samples for which the resistivity is not lin ear in temperature. At low doping (x less-than-or-equal-to .15) the ex ponent is m = (2.1 +/- .1). The simple quadratic temperature dependenc e of the mobility is evidence for fermion-fermion scattering. This is supported by the fact that the absolute mobility decreases with the ho le content x. It shows that the direct coupling between the holes is t he dominant interaction in the normal state of La-214. At higher dopin g (x greater-than-or-equal-to .18) the exponent decreases to m congrue nt-to 1.7 indicating a change in the scattering mechanism.