Study on the d-p model by the Numerical Diagonalization Method

为了弄清高温超导的机理，我们采用数值对角化方法对一维d-p模型进行了研究。该模型包含铜（d-）位和氧（p-）位之间的电子跳变和两个位置上的排斥性库仑相互作用。此外，它还包含最近邻p相互作用和最近邻p位点之间的跳跃tpp。它被认为是研究高温超导可能机制的一个很好的目标。通过计算基于Luttinger液体关系的配对相关函数和临界指数，我们分析了d位的大排斥力Ud与转移能tpp共同作用所诱导的超导态。我们发现，在重整带变平的参数区附近，超导相关占主导地位。各种配对相关函数的行为表明，最近相邻p位之间的单线态配对与超导态最相关。我们还发现，d-p模型的低能物理很好地描述了t-J模型。有效带宽的变窄导致有效超交换相互作用比有效传输J/t值的增大。在d-p模型中可以产生超导性，在t-J模型中，J/t的增强可以产生超导性。

HEAD INVESTIGATOR REGISTERED NUMBER 40201537 NAME Kazuhiro, Sano Department of Physics Engineering, Mie University Assistant ProfessorToward the clarification of the mechanism of the high temperature superconductivity, we investigate the one-dimensional d-p model by the numerical diagonalization method. The model contains electron hopping between copper (d-) site and oxygen (p-) site and repulsive Coulomb interaction on both sites. In addition, it contains the nearest-neighbor-p interaction and the hopping tpp between the nearest-neighbor p sites. It is known as a good target for investigating the possible mechanism of the high-Tc superconductivity.By calculating the paring correlation functions and the critical exponent based on the Luttinger liquid relations, we analyzed the superconducting state induced by the effect of the large repulsion Ud at the d-site in cooperation with the transfer energy tpp. We have found that the superconducting correlation is dominant in the proximity of the parameter region where the renormalized band becomes flat. The behavior of various types of the paring correlation functions suggests that the singlet paring between the nearest neighbor p sites is the most relevant to the superconducting state.We have also found that the low energy physics of the d-p model is well described by the t-J model. The narrowing of the effective bandwidth leads to the enhancement of the value of the effective superexchange interaction over the effective transfer J/t. It may originate the superconductivity in case of the d-p model as well as the enhancement of J/t causes the superconductivity in the case of the t-J model.