Structural transition in Bi-Sr-Ca-Cu-O revealed by Fermi level control and the mechanism of high-T_csuperconductivity

Abstract

A technique is developed for control of the Fermi level in ms materials by the oxygen dosage in the sample using a solid-state electrochemical cell. The dependences of the ovaen content in the sample n(,EF) an0 tne electron density of states et the Fermi level D ( E F ) on the Fermi level have been studiedAt a separation of several tens of mV above the Fermi level of the ms state, an n(Ep) step and D(&) peak are revealed which are relate0 to the struttural phase transition. The cnaracter of the dependences obtained allows us to relate high-temperature superconductivity to the interaction between the virtual structural phase transhion and the transition to the conventional superconducting state In the phenomenological model proposed this interaction is described by IWO order parameters: J the superconductive gap width, and ti the energy separat'ng the superconducting state from the v;nual structural phase transition.In the microscopic mddel under consideration this interaction results in the appearance of an electron-phonon gap above the Fermi level. The position of the gap increases the electron density of slater; In the region of BCA interaction with phonon, thus excluding dielectrization of the electronic spectrum.