Influence of atomic-scale inhomogeneity of the pair interaction on the local pair formation and density of states of high-Tc superconductors

Abstract

The influence of the atomic-scale inhomogeneities of the pairing interaction strength on the superconducting order parameter and the conductance spectra measurable by scanning tunneling microscopy (STM) is studied in the framework of weak-coupling Bardeen-Cooper-Schrieffer (BCS)-like theory for two-dimensional lattice model. First of all, it is found that the inhomogeneity having the form of atomic-scale regions of enhanced pair interaction increases the ratio of the local low-temperature gap in differential conductance spectra to the local temperature of vanishing the gap 2Δg/Tp. Even in the framework of mean-field treatment, this ratio is shown to be larger than the one corresponding to the homogeneous case. It is shown that the effect of thermal phase fluctuations of the superconducting order parameter can further increase this ratio. Taking them into account in the framework of a toy model, we obtained the ratio 2Δg/Tp to be ∼7−8. It is found that the additional atomic-scale hopping element disorder and weak potential scatterers, which can also take place in cuprate materials, have no considerable effect on the statistical properties of the system, including the distribution of the gaps, Tp and the ratio 2Δg/Tp. The second consequence of the atomic-scale order parameter inhomogeneity is the anticorrelation between the low-temperature gap and the high-temperature zero-bias conductance. The obtained results could bear a relation to recent STM measurements.

Source-reported materials — not catalogue approval

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