低维体系的不稳定性和电子关联  

INSTABILITY AND ELECTRON CORRELATION IN LOW-DIMENSIONAL SYSTEMS

作　　者：孙鑫[1] 吴长勤[2] 刘晶南 傅柔励[3] 

机构地区：[1]复旦大学物理系 [2]南京大学固体微结构物理实验室 [3]中国科学院上海技术物理研究所红外物理开放实验室

出　　处：《物理学进展》1990年第4期439-471,共33页Progress In Physics

基　　金：国家自然科学基金863-715资助

摘　　要：一维和二维体系的费米面会呈现叠套(nesting),于是,晶格结构和电子状态的重新调整(使费米面和布里渊区边界相互重合)可使体系能量降低而形成新的基态,这使低维体系具有不稳定性并产生相变,同时还会形成多种新型元激发(电荷密度波(CDW)、自施密度波(SDW)、孤子(soliton)、极化子(polaron)、分数电荷,spin bag,位相子等)。许多重要的低维体系(导电高分子、二维电子气、氧化物超导体的铜氧层等)都具有强电子耦合5研究电子关联对体系不稳定性的影响是当前凝聚态物理的重要课题。近年来,在此领域内,有两派相反的观点进行着激烈的争论:一派认为电子-电子相互作用会增强晶格不稳定性,而且增强得很多,以致不稳定性主要来自于电子-电子相互作用,电子-晶格相互作用是次要的。另一派则认为电子-电子相互作用会减弱晶格不稳定性,而不稳定性是由电子-晶格相互作用产生的。 本文首先描绘低维体系的不稳定性和各种基态及元激发的物理图象,接着介绍争论双方的论点,随后分析两派分歧的产生原因,进一步指出如何澄清这场争论。从中将说明,Hubbard模型的局限性会带来问题,解决争论的关键是正确地描述电子相互作用,由屏蔽效应而形成的相互作用力程是决定性的因素。当屏蔽较弱时(长程相互作用)。The Fermi surface of one and two-dimensional systems can present nesting structure, then the adjustment of lattice structure and electron state, which makes the new Brillouin zone coincide with the Fe rmi surface, will lower the system's energy and reach new ground state. It induces the instability and causes the phase transition in low-dimensional systems. Associating with these resultant ground states,many new sorts of elementary excitations emerge, which include CDW, SDW, soliton, polaron, fractional charge, spin bag, phason etc. Many important low-dimensional systems such as conducting polymers, two-dimensional electron gas, oxide high Tc superconductors possess strong electron correlation. It is a significant subject to study the effect of electron correlation on the instability of low-dimensional systems. Recently in this area there wages a heated dispute between two schools with opposite opinions. One school declares that the electron-electron interaction so greatly enhances the instability that the main cause of the instability is the electron-electron interaction rather than the electron-lattice interaction. But, on the contrary, the other school believes that the electron-electron interaction reduces the instability, and the instability itself is produced by the electron-lattice interaction. The former is the Mott Mechanism, and the latter is the Peierls mechanism. This paper depicts the physics pictures of various new ground st-ates and elementary excitations in different low-dimensional systems. We also point out how to clarify the above dispute. It is found that the range of interaction is the decisive fact. In the case of long interaction range, the off-diagonal part of electron interaction is much smaller than the diagonal one, then the site-charge repulsion enhances the lattice instability; Contrary, in the case of short interaction range, the off-diagonal part can compete with the diagonal one, then the bond-charge repulsion restralns the instability.

关 键 词：低维体系 不稳定性 凝聚态物理 

分 类 号：O4[理学—物理]