Variable range hopping in the spin-glass phase of La2-xSrxCuO4

The results of the in-plane transport measurements of strongly underdoped La2-xSrxCuO4 films in magnetic fields up to 14 T and at temperatures down to 1.6 K are presented. While at high temperatures the resistivity of the films is metallic-like, the low-T transport is governed by the variable range hopping (VRH) mechanism. Careful analysis shows that the temperature dependence of the pre-exponential factor in Mott's VRH law cannot be neglected and the zero-field conductivity is best described by the formula σ = σ0T-2wexp[-(T0/T)w]. In a magnetic field parallel to CuO2 planes the VRH law is retained, with both parameters, σ0 and T0, decreasing by about 10-20% at 14 T. This effect may be related to the decrease of the tunnelling barrier between different antiferromagnetic clusters in the presence of a magnetic field