Abstract
We study the inhomogeneity of the pairing gap near the surface of Bi2Sr2CaCu2O8+δ due to interstitial oxygen dopants. Within the slave boson mean-field theory of a disordered t–t′–J model, we identify three aspects of the oxygen dopants related to inhomogeneity: (i) the superexchange interaction is locally enhanced in the vicinity of oxygen dopants, which enhances the local pairing gap and reduces the coherence peak; (ii) oxygen dopants donate holes into the CuO2 plane, which reduces the spinon density of states and hence the average gap at large doping; and (iii) holes are locally attracted to the vicinity of oxygen dopants, which causes an impurity bound state and further reduces the coherence peak. The interplay of these mechanisms simultaneously explains the locally enhanced pairing gap around oxygen dopants and the reduction of average gap with increasing oxygen concentration, as observed by scanning tunneling microscopy.
Highlights
The effect of disorder in high-Tc cuprates, either intentionally introduced or present as a result of the doping process, has always been crucial to their practical applications
We have presented a slave boson mean field approach to compare the possible physical effects induced locally by oxygen dopants near the surface of BSCCO, and show how their interplay can explain the pairing gap revealed by STM experiments
The enhancement of the pairing gap and reduction of coherence peak near oxygen defects is attributed to locally enhanced pairing interaction via superexchange
Summary
The effect of disorder in high-Tc cuprates, either intentionally introduced or present as a result of the doping process, has always been crucial to their practical applications. The simulation that contains both pairing and hopping enhancement is shown, where one sees that the superconducting gap is enlarged as expected, and the coherence peak is further reduced compared to the case that contains only an off-diagonal impurity. If the impurity locally reduces both the pairing and hopping interactions, the gap is reduced and the coherence peak height increases This simulation suggests that the change in the local hopping amplitude, whose origin can be traced back to the holon accumulation due to strong correlations, plays an important role in the shape of STM spectrum, the weight of coherence peak. We apply the following mean field decoupling to the Heisenberg term
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