From nonmetal to strange metal at the stripe-percolation transition in La 2-x Sr x CuO 4

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 La (2 - x) Sr- x CuO 4 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 CuO 2 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.