Quantum Phase Transitions in Strongly Correlated Electron Systems

强相关电子系统中的量子相变

• 批准号: 11694074
• 负责人: SIGRIST Manfred W.
• 金额: $ 1.54万
• 依托单位: KYOTO UNIVERSITY
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 1999
• 资助国家: 日本
• 起止时间: 1999 至 2000
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-11694074/
• 关键词: Quantum phase transition; Strongly correlated electron system; Magnetism; Spin gap; Random spin system; Kondo lattice; Unconventional superconductivity; Non-magnetic impurity; Quantum phase transition; Strongly correlated electron system; Magnetism; Spin gap; Random spin system; Kondo lattice; Unconventional superconductivity; Non-magnetic impurity

The exact ground state and the excitation spectrum of the Shastry-Sutherland spin system, and the presence of magnetization plateaus and their properties have been analyzed. Furthermore the possible quantum phase transition within this model has been studied. This problem applies to SrCu_2(BO_3)_2, which is a system close to a quantum critical point.The elimination of the quantum phase transitions due to impurity effects in two-dimensional plaquette RVB systems was analyzed by means of stochastic series expansion.Quantum phase transition in systems with dimerized, plaquette or mixed spin structures : the conditions for the transition between a valence-bond solid and various magnetically ordered plases have been analyzed for various cases.The low-energy properties of the SU(4)-symmetric Kugel-Khomskii chain with spin and orbital (isospin) degrees of freedom have been studied analytically from symmetry point of view and numerically. The multi-orbital effects have been investigated for Ca-doped Sr_2RuO_4 based on localized spin and orbital degrees of freedom which occur in an orbital-dependent Mott-transition.The ground state and low-energy properties of the (geometrically frustrated) pyrochlore systems with spin-1/2 and spin-1 degrees af freedom have been studied, in view of the quantum phase transition driven by large residual entropy, including Jahn-Teller type of deformations.The Luttinger liquid behavior was investigated in the doped Kondo lattice model, where a new small energy scale appears.The relation between magnetic correlation and the unconventional superconductivity was studied for the case of the spin-triplet superconductor Sr_2RuO_4.Properties of the low-energy quasiparticle density of states and localization effects in quantum wires and coupled chains with off-diagonal disorder have been classified.

已经分析了精确的基础状态和Shastry-Sutherland自旋系统的激发光谱，并且已经分析了磁化高原及其性质的存在。此外，已经研究了该模型中可能的量子相变。该问题适用于SRCU_2（BO_3）_2，该系统是接近量子临界点的系统。消除二维PLAQUETTE RVB系统在二维Plaquette RVB系统中由于杂质效应而导致的量子相变过渡，通过随机串联膨胀的方式分析了固体和混合旋转结构条件的随机串联延伸的方式。已经分析了各种情况的有序木板。SU（4） - 对称的Kugel-Khomskii链的低能特性具有自旋和轨道和轨道（Isospin）自由度，从对称的观点和数值上研究了分析研究。已经根据轨道依赖性的Mott-Mott-Transition中的局部旋转和轨道自由度研究了CA掺杂的SR_2RUO_4的多轨效应。基的状态和低能特性（（几何非常沮丧）的Pyrochlore系统，具有旋转1/2和自旋的量子自由度的量子，该系统的量子是跨度的。在掺杂的Kondo晶格模型中研究了Luttinger液体行为，其中出现了新的小能量量表。在量子线和耦合链中，患有异对决障碍的链已被分类。