Soft-phonon behavior and transport in single-crystalLa2CuO4

Using a flux technique we have grown sizable single crystals of ${\mathrm{La}}_{2\mathrm{-}\mathrm{x}}$ ${\mathrm{Sr}}_{\mathrm{x}}$ ${\mathrm{CuO}}_4$. With x rays and neutrons we have studied both the static and dynamic aspects of the tetragonal to orthorhombic structural phase transition; classic soft-phonon behavior is observed at the ((1/2, 1) / 2 , 0) zone boundary involving rotations of ${\mathrm{CuO}}_6$ octahedra. The pure and lightly-doped single crystals show hopping conductivity, lnρ∼($T_0$/T${)}^{1/4}$, indicating that the electronic states at the Fermi energy are localized.