Anisotropies in the optical ac and dc conductivities in lightly doped La2-xSrxCuO4: the role of deep and shallow acceptor states

作者：Silva Neto M B; Blumberg G; Gozar A; Komiya Seiki; Ando Yoichi

来源：Journal of Physics: Condensed Matter , 2011, 23(21): 215602.

DOI：10.1088/0953-8984/23/21/215602

We investigate the origin of the optical ac and dc conductivity anisotropies observed in the low temperature orthorhombic phase of lightly doped, untwinned La2-xSrxNiO4 single crystals. We show that these anisotropies can be naturally ascribed to the emergence of two odd parity, rotational-symmetry-broken, localized impurity acceptor states, one deeper and one shallower, resulting from the trapping of doped holes by the Coulomb potential provided by the Sr ions. These two lowest-energy, p-wave-like states are split by orthorhombicity and are partially filled with holes. This leaves a unique imprint in the optical ac conductivity, which shows two distinct far-infrared continuum absorption energies corresponding to the photoionization of the deep and shallow acceptor states. Furthermore, we argue that the existence of two independent and orthogonal channels for hopping conductivity, directly associated with the two orthorhombic directions, also quantitatively explains the observed low temperature anisotropies in the dc conductivity.

• 出版日期2011-6-1