The Quasi-Particle Density of States of Optimally Doped Bi 2212: Break-Junction vs. Vacuum-Tunneling Measurements

Abstract

In the present article we show that a strong-coupling density of states (DOS) with a d _x ²−y² symmetry, determined by direct solution of the d-wave Eliashberg equations in the real energy axis formulation, can represent very well our best break-junction optimally-doped Bi 2212 tunneling data and explain their T_c, if we use an electron-boson spectral function determined by the inverse solution of the same equations in s-wave symmetry. In contrast, even by using spectral functions of different kind, it is impossible to obtain a good fit of the DOS and, at the same time, of T_c in the best Bi 2212 STM measures by means of the d-wave Eliashberg theory. It is also clear that the low-temperature zero-bias DOS is not fully consistent with a pure d-wave symmetry and other mechanisms, as a modest impurity scattering in the unitary limit, have to be considered in order to explain the low-energy data.