Role of excess oxygens in cuprates

銅酸化物における過剰酸素の役割

森 道康  

Mori, Michiyasu

Local disorder by chemical doping triggers nanoscale inhomogeneities commonly observed in cuprates. Recent experiments on Bi-based cuprate superconductors have revealed an unexpected enhancement of the pairing correlations near the interstitial oxygen dopants. We proposed a possible mechanism based on local screening effects, by which the oxygen dopants do modify the electronic parameters within the CuO planes and strongly increase the superexchange coupling J. This enhances the spin pairing effects locally and may explain the observed spatial variations of the density of states and the pairing gap. In order to estimate the typical length scale measured in the experiment, we will examine the t-J model including the local modulation of J by using the numerical simulation method. In our mechanism, the dopant oxygens may indeed strongly enhance the interaction J locally. Our key idea is to go beyond static level structure used in standard calculations of J, by taking account of a dynamical change of electronic parameters due to polarization effects.