From nonmetal to strange metal at the stripe-percolation transition in La2-xSrxCuO4

The nature of the normal state of cuprate superconductors continues to stimulate considerable speculation. Of particular interest has been the linear temperature dependence of the in-plane resistivity in the low-temperature limit, which violates the prediction for a Fermi liquid. We present measurements of anisotropic resistivity in La2-xSrxCuO4 that confirm the strange-metal behavior for crystals with doped-hole concentration p=x>p∗∼0.19 and contrast with the nonmetallic behavior for p<p∗. We propose that the changes at p∗ are associated with a first-order transition from doped Mott insulator to conventional metal; the transition appears as a crossover due to intrinsic dopant disorder. We consider results from the literature that support this picture; in particular, we present a simulation of the impact of the disorder on the first-order transition and the doping dependence of stripe correlations. Below p∗, the strong electronic interactions result in charge and spin stripe correlations that percolate across the CuO2 planes; above p∗, residual stripe correlations are restricted to isolated puddles. We suggest that the T-linear resistivity results from scattering of quasiparticles from antiferromagnetic spin fluctuations within the correlated puddles. This is a modest effect compared to the case at p<p∗, where the data suggest that there are no coherent quasiparticles in the normal state.