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

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.

分析了Shastry-Sutherland自旋系统的精确基态和激发谱，以及磁化平台的存在及其性质。此外，还研究了该模型中可能发生的量子相变。这个问题适用于接近量子临界点的系统--SrCu2(BO_3)_2。用随机级数展开的方法分析了二维板状RVB系统中杂质效应引起的量子相变的消除。分析了二聚化、板状和混合自旋结构体系的量子相变：分析了价键固体和各种磁性有序相之间的相变条件。从对称性的角度和数值方法研究了具有自旋和轨道(同位旋)自由度的SU(4)对称Kugel-Khomskii链的低能性质。基于轨道相关的Mott跃迁中的局域自旋和轨道自由度，研究了掺Ca的Sr2RuO4的多轨道效应.考虑到大的剩余熵驱动的量子相变，包括Jahn-Teller类型的形变，研究了具有自旋-1/2和自旋-1自由度的焦绿石(几何受挫)系统的基态和低能性质.在掺杂的Kondo晶格模型中研究了Luttinger液体行为.以自旋三重态超导体Sr2RuO4为例，研究了磁关联与非常规超导电性的关系。对非对角线无序量子线和耦合链的低能准粒子态密度和局域效应的性质进行了分类。

项目成果

H.Aoki,A.Ochiai,M.Oshikawa and K.Ueda.: "Magnetic Anisotropy in Yb_4As_3 with One-dimensional Yb^<3+> Chains"Physica B. 281&282. 465-467 (2000)

H.Aoki、A.Ochiai、M.Oshikawa 和 K.Ueda.：“具有一维 Yb^<3 > 链的 Yb_4As_3 中的磁各向异性”Physica B. 281

P.W.Brouwer,C.Mudry and A.Furusaki: "Density of States in Coupled Chains with Off-Diagonal Disorder"Physical Review Letters. 84. 2913-2916 (2000)

P.W.Brouwer、C.Mudry 和 A.Furusaki：“非对角无序耦合链中的态密度”物理评论快报。

S.Miyahara and K.Ueda: "Superstructures at Magnetization Plateaus in SrCu_2(BO_3)_2"Physical Review B. 61. 3417-3424 (2000)

S.Miyahara 和 K.Ueda：“SrCu_2(BO_3)_2 磁化平台的上部结构”物理评论 B. 61. 3417-3424 (2000)

M.Sigrist et al: "Phenomenology of the superconducting state in Sr_2RuO_4"Physica C. 317-318. 134-141 (1999)

M.Sigrist等人：“Sr_2RuO_4中超导态的现象学”Physica C. 317-318。

A.Koga,S.Kumada and and N.Kawakami: "Quantum Phase Transitions in Two-Dimensional Spin Systems with Ladder, Plaquette and Mixed-Spin Structures"Journal of the Physical Society of Japan. 68. 2373-2379 (1999)

A.Koga、S.Kumada 和 N.Kawakami：“具有阶梯、斑块和混合自旋结构的二维自旋系统中的量子相变”日本物理学会杂志。