High-field magnetotransport of epitaxial La2-XSrXCuO4 thin films in the regime of low Sr-doping

High temperature superconductors have an unusual temperature (T) - doping ( x) phase diagram, in which both antiferromagnetism and superconductivity oc cur. The spin gap and the superconducting gap are the two essential feature s of the T(x) plane which evolve with doping. A material allowing investiga ting the T-x plane in detail, from the underdoped (x<0.15) to the overdoped (x>0.15) regime, is the La2-xSrxCuO4 superconductor. The temperature depen dence of the resistivity strongly depends on the substitution ratio x. Over doped films show metallic behavior, meaning that rho (T) is linear above 10 0 K, while it saturates for lower temperatures. This saturation persists be low T,, when superconductivity is suppressed by sufficiently high pulsed ma gnetic fields. From the slightly overdoped (0.2 < x) down to the strongly u nderdoped regime (x <similar to> 0.03) we observe, instead of saturation, a rho (T) dependence with logarithmic divergence in the field-induced normal state at T --> 0. For underdoped films (x < 0.1) a superlinear pm behavior develops at intermediate temperatures (50 K < T < 200 K), indicating the o pening of the spin gap.