AC and DC Conductivity Anisotropies in Lightly Doped La(2-x)Sr(x)CuO(4)
  The AC and DC conductivity anisotropies in the low temperature orthorhombic phase of lightly doped La(2-x)Sr(x)CuO(4) are ascribed to the rotational symmetry broken, localized impurity states resulting from the trapping of doped holes by Sr ions. The two lowest-energy p-wave-like states are split by orthorhombicity and partially filled with holes. This leaves a unique imprint in AC conductivity, which shows two distinct infrared continuum absorption energies. Furthermore, the existence of two independent channels for hopping conductivity, associated to the two orthorhombic directions, explains quantitatively the observed low temperature anisotropies in DC conductivity. 
M. B. Silva Neto, G. Blumberg, A. Gozar, Seiki Komiya, Yoichi Ando