Novel Insulator to Metal Transition and Superconductivity in Sr-doped La2CuO4

Abstract

We have studied the charge dynamics of Sr-doped La2CuO4 at hole concentration p =0.07. We observed a clear indication of the competition between two new characteristic collective modes of the Wigner lattice orders suggested earlier: one corresponds to a Tc =15 K superconductivity and the other to Tc =30 K. Our results naturally explain the recent observation of metallic transport in extremely low (1%) Sr-doped La2CuO4 and establish a novel insulator to metal transition mechanismand superconductivity in the two-dimensional Wigner lattice ground state. We suggest that the fluctuations of the relative phase between the superconducting condensate and the Wigner lattice order can provide an answer to the unidentified mode in the c-axis conductivity that appears only below Tc.