Transport properties of La2-xSrxCuO4 epitaxial thin films in high magnetic fields

We have investigated the magnetotransport of La2-xSrxCuO4 (0.045≤x≤0.25) epitaxial thin films in pulsed fields up to μ0H=50 T. Above a certain temperature T*, the temperature dependence of the resistivity ρ(T) is linear and between T* and the superconducting critical temperature Tc, ρ(T) is superlinear. This observation is universal for all underdoped films. The high field data ρ(T,H0) from underdoped and slightly overdoped samples reveal a metal-to-insulator like transition (MIT) at low temperatures. We have determined the detailed dependence of the minimum in the ρ(T) curves as a function of the Sr-content x. The MIT can be analyzed by calculating the kFl product from the resistivity data; here kF is the Fermi wave vector and l is the mean free path. We can describe the insulating behavior at low temperatures of samples with kFl<1 by a variable range hopping conductivity. For samples where kFl>1 the divergence of the resistivity follows a power (T-α(α>0)) or a logarithmic (ln(1/T)) law, depending on the Sr-content. This ρ(T) divergence is probably associated with the formation of the pseudogap and the pinning of the fragmented charge stripes at low temperatures