Anticorrelation between the parent charge transfer gap and maximum transition temperature in cuprates

We use scanning tunneling spectroscopy to measure the electronic structure of the parent Mott insulator of three different types of cuprates. The charge transfer gap size exhibits pronounced variations, and more interestingly it shows an anticorrelation with the maximum superconducting transition temperature achieved at the optimal doping of each cuprate. This result suggests that the Mottness in parent cuprate plays a crucial role in determining the superconducting properties. In particular, reducing the electron correlation strength enhances superconductivity, which is consistent with the pairing mechanism based on the doped Mott insulator picture.