Transport properties at the insulator-superconductor phase boundary of La2-xSrxCuO4 thin films

The longitudinal resistivity and the transverse Hall resistivity of La1.94S r0.06CuO4 and La1.97Sr0.03CuO4 epitaxial thin films are investigated. The z ero-field resistivity rho (T) of La1.94Sr0.06CuO4 shows a minimum at 80 K a nd a resistive midpoint of the superconducting transition at T-c(mid) appro ximate to 7.5 K. A magnetic field of 8 T suppresses the superconducting sta te and induces a semiconducting normal state with rho (T) increasing with d ecreasing temperature. The resistivity of La1.97Sr0.03CuO4 has a minimum at 100 K and no superconducting transition is observed down to 1.5 K. The sem i conducting low-temperature behaviour can be described by Shlovskii-Efros hopping, while the metallic-like regime corresponds to 1D quantum transport of charge stripes. The field dependence of the Hall resistivity rho (xy)(B ) has an opposite behaviour for the two doping levels: the rho (xy)(B) slop e of La1.94Sr0.06CuO4 decreases with decreasing temperature, while it incre ases in the case of La1.97Sr0.03CuO4. Within the superconducting transition regime of La1.94Sr0.06CuO4 (below 15 K) we observe a sign inversion of rho (xy)(B) in the limit of weak magnetic fields. (C) 2001 Elsevier Science B. V. All rights reserved.