From nonmetal to strange metal at the stripe-percolation transition in La_2−xSr_xCuO₄

In the superconducting system La_2-xSr_xCuO₄, strange-metal behavior has been observed in the low-temperature resistivity for doped-hole concentrations p from the crossover point p* ~ 0.19 to the critical value where superconductivity disappears. We have confirmed such behavior in crystals in which we had previously observed evidence for superconducting puddles. The presence of such puddles can be explained in terms of spatial variations of p due to the random distribution of Sr dopants. In this picture, the superconducting patches are associated with lower hole concentrations where strong correlations lead to charge and spin stripe correlations. A variety of properties can be modelled in terms of a sharp transition at p* from nonmetallic superconductor to normal metal, where the transition becomes a crossover as a consequence of dopant disorder. The mixture of strongly-correlated puddles in a metallic matrix appears to underlie the strange-metal behavior in this system.