Electronic structure of the CuO-chain layer in YBa2Cu3O7-δ studied by scanning tunneling microscopy -: art. no. 140511

Low-temperature scanning tunneling microscopy measurements have been performed on YBa2Cu3O7-delta single crystals with various oxygen contents (6.65less than or equal to7-deltaless than or equal to6.98). In the CuO-chain layer, we observe the doping-dependent charge modulation images that are attributed to the charge-density wave (CDW) due to the 2k(F) instability of the one-dimensional Fermi surface. Even in the so-called 60-K T-c plateau region, the CDW correlation in the CuO-chain layer survives partially. Our scanning tunneling microscopy results indicate that the CuO chain without oxygen vacancies is 1/4 filled and prefers to form a CDW state.