文档介绍：摘要
摘要
本文在t-J-U模型和Gutzwiller平均场理论的框架下,对铜氧化物高温超导材料基态相图以及电子的次近邻跃迁对相图的影响进行了较为系统的研究。第一章简单介绍了可以描述Cu02平面内基本的低能物理过程的t—,并介绍了目前国际上公认的可以较好的处理电子之间强相互作用的Gutzwiller平均场近似。
应用Gutzwiller平均场理论,第二章系统地讨论了铜氧化物高温超导材料基态时的相图:首先从t-j-u模型出发系统地研究了gossamer超导体中d波超导和反铁磁的相互作用。得到了基态情况下铜氧化物高温超导材料的相图。在标准参数t/J=3 和大U极限下,。随着掺杂浓度的增大,d波超导序参数从0开始增加,。在小U的极限下,只有d波超导序存在,而反铁磁序消失。当U 增大到一定临界值,反铁磁序出现并在欠掺杂区域和d波超导序共存。在半满的情
况下,我们研究的系统在U较小时为gossamer超导,在大u情况为反铁磁绝缘体。第三章讨论了电子次近邻跃迁对基态相图的影响。结果发现,在目前的理论框架下t-t’.“.U模型的性质定性一样,但是随着电子次近邻跃迁的增大,超导序参数在欠掺杂区域受到抑制,在最佳掺杂和过掺杂区域得到加强,从而导致反铁磁序和d波超导序共存区域变大,d波超导序在很大的掺
杂浓度范围内一直存在,这和相关数值模拟结果定性相符。
关键词:gossamer超导体,Gutzwiller平均场近似,d波超导序,
反铁磁序
Abstract
Wi也iIl the t-J-U mode and Gutzwiller mean-field approximation,the ground state
phase diagram and the influence of the additional second-neighbor hopping t on the
phase diagram of the copper oxide materials are studied systemically.
们舱paper anized as Chapter I,a brief review of the development of cuprate material is we introduce the t-J-U model which is able to describe the essential low—energy physics of cuprates and the Gutzwiller mean-field approximation which Can treat the strong correlation between the electrons properly.
Within the t-J—U mode and Gutzwiller mean—field approximation,the phase diagrams of gossamer superconductors are studied in Chapter II:firstly,we study the d—wave superconductivity(dSC)and ism(AF)in a renormalized mean field theory.
弧e phase diagrams as functions of doping 6 and U are the standard value
of tZJ= and in the large U limit,we find mat the AF order emerges and coexists with the
dSC in the underdoped region below the doping dSC order parameter increases from zero as the doping increases and reaches a maximum near the optimal doping 5. In the small U limit,only the dSC order survives while the AF order U increases up to a critical value,the AF order shows up and coexists