%0 Journal Article
%T The Role of Polarons in Cuprates Hi- Superconductivity
%A M. I. Umo
%J Indian Journal of Materials Science
%D 2014
%R 10.1155/2014/590928
%X The phonon contribution to the phenomenon of high temperature superconductivity in the cuprates is argued as being masked as polarons generated by the polarization of the charge reservoir accompanying the Jahn-Teller tilting of the apical oxygen. We discuss the Mahan oscillator-spring extension model as an analogy to the charge reservoir-CuO plane -axis polarons. Using the Boltzmann kinetic equation, we show that the polaron dissociates or collapses at a temperature corresponding to the critical temperature of the superconductor. 1. Introduction Almost three decades since the discovery of high temperature superconductivity in the cuprate La-Ba-CuO by Bednorz and Muller [1] and subsequently in many CuO based compounds by other researchers, there is still no closure about the mechanism of superconductivity in these systems [2, 3]. One of the major points of disagreement is whether phonons contribute along with the accepted spin magnetic fluctuation to the high critical temperature of the cuprates. Many researchers are in support of the phonon mechanism as the only factor responsible for the cuprates high critical temperatures [4¨C6]. Other workers [7¨C9] have considered the spin magnetic fluctuation the only adoptable theory for the cuprates. A good reason for the persistence of the ¡°phonon-camp,¡± is perhaps the enduring success of the electron-phonon interaction (EPI) explanation of the low temperature superconductivity (LTS) by Bardeen, Cooper, and Schrieffer (BCS), [10]. Still another reason may be the recent discovery of superconductivity in MgB3 at £¿K [11]; this being explained surprisingly by the EPI mechanism. It has even become very comfortable to make prognosis of still higher ¡¯s in materials whose electronic properties are well understood based on the EPI. As an example we mention the EPI mechanism used by Gao and his coworkers to predict that the compound Li2B3C superconducts at about 50£¿K through the process of lifting the -bonding up above the Fermi level by doping, enabling -electrons to interact strongly with the lattice vibrations in such a way that electron pairing occurs [12]. In the LTS such as lead, tin, and aluminium, phonon contribution is indicated by the isotope effect which relates the critical temperature ( ) to the mass ( ) of the isotope atom as , where is the electron-phonon coupling constant defined as . The BCS value for is [13] which corresponds to the weak coupling regime where the Coulomb interaction is neglected. When the Coulomb interaction is taken into account, can be approximated by , where and is the BCS interaction
%U http://www.hindawi.com/journals/ijms/2014/590928/