准一维磁性分子固体及相关磁系统中的量子相变研究

项目名称： 准一维磁性分子固体及相关磁系统中的量子相变研究

项目编号： No.10874132

项目类型： 面上项目

立项/批准年度： 2009

项目学科： 金属学与金属工艺

项目作者： 王为忠

作者单位： 武汉大学

项目金额： 36万元

中文摘要： 固体磁性分子有望成为分子电子学及自旋分子电子学的最基本结构单元，量子点可看作人工分子。本项目主要研究了具有强关联电子（或磁性）相互作用的量子点系统中的电磁输运性质及量子相变。例如，对具有在位HUBBARD相互作用的三量子点系统，如在垂直于三量子点所形成的环面加上磁通，则由于Aharonov-Bohm干涉效应会产生三阶超交换作用， 而且该超交换作用可以诱导一个可调的Kosterlitz-Thouless（KT）型量子相变；在两量子点系统中，在无外磁场时，当量子点间库伦相互作用增大到与量子点内在位HUBBARD相互作用相当时，系统发生从局域三重态到单重态的KT型量子相变，当磁场增大到一临界值时，系统发生二级量子相变；如两量子点与无自旋偏振的电极相连，通过改变两量子点的轨道能量差，系统发生从局域三重态到双重态的KT型量子相变，如电极有自旋偏振，上述量子相变变成一级的，而且可以观察到Kondo分裂及完美的自旋过滤现象。我们还研究了一维Hubbard超格子中的带绝缘体，Mott绝缘体及键序相，发现了无公度的电荷关联相；对一维具有近邻及次近邻电子相互作用的无费米子系统，发现键序关联及其静态结构因子

中文关键词： 分子电子学；量子点；Kondo效应；量子相变

英文摘要： Magnetic molecule may become componentes in molecular electronics and spin molecular electronics. Quantum dots can be regarded as artificial molecules. In this project, we have studied the electronic and magnetic transports and the quantum phase transition (QPT) in strongly correlated quantum dots systems. For instance, In a triple quantum dot pierced by an external magnetic flux, wefind that the third-order superexchange interaction survives due to Aharonov-Bohm interference and induces a magnetically tunable Kosterlitz-Thouless (KT) QPT between local singlet and triplet. In a double quantum dot system with on-site repulsion U, interdot repulsion V, and magnetic field B, there is a local spin triplet-singlet KT transition for B=0 when V increases to a critical value Vc ≈U while with increasing B, a singlet-triplet transition of the second order occurs at a critical magnetic field Bc ≈V . In double quantum dots attached to spin-polarized leads, for spin-independent leads, we observe a KT transition between the local triplet and doublet while for spin-polarized leads, the above QPT becomes first order, and Kondo splitting, gate-controlled spin reversal and a perfect spin filtering are observed. In a half-filled one-dimensional superlattice Hubbard model with an alternating orbital energy ±_/2 and on-site Coulomb repulsion UA and UB, we study the band insulator, Mott insulator and the bond order phase and observe an incommensurate charge correlation phase. For a spinless fermion model with the nearest and next-nearest-neighbor repulsions, we find that the bond-order (BO) correlation function and its static structure factor can be employed to accurately determine the BO phase boundaries.

英文关键词： molecular electronics; quantum dot; Kondo effect; quantum phase transition.