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Metal-insulator Transition on a Half Filled Triangular Lattice

Author: GaoJiMing
Tutor: WangJiaXiang
School: East China Normal University
Course: Theoretical Physics
Keywords: Extended Hubbard model Metal - insulator transition Critical exponents Spin density wave Charge density wave Pester
CLC: O469
Type: Master's thesis
Year: 2009
Downloads: 50
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Abstract

Metal - insulator transition is condensed matter physics is one of the important issues, especially in the electrical conductivity of organic compounds of the study, it was found that many organic compounds applied pressure will occur in the case of complex metal - insulator quantum phase transition, such as κ-(BEDT-TTF) ₂ X and so on. Moreover, these compounds have a strong two-dimensional triangular geometry associated conductive layer. Triangular lattice structure is a geometric frustration, the use of the Hubbard model, the existing research results show that the half-filled triangular lattice interactions in particular reign (U / t> 0) occurs metal - insulator transition, where U the two electronic grid points in the same place when repulsion, t is the transition between the adjacent lattice points interactions. This is a half-filled with a great difference grid points, the grid point, the phase transition point occurs at U / t = 0, i.e. if U> 0, the system is in an insulating state. Thus, the general view in the physical model is introduced to help people understand the frustration factor strongly correlated materials, semi-filler metal - insulator transition of key steps. In addition to the geometry, the system's long-range interaction is also a frustration factor, and the conductivity of the system can have an important impact. In order to explore two kinds of frustration factors exist, the system changes the nature of how we apply real space renormalization group method, the half-filled extended Hubbard model on a triangular lattice of the metal - insulator quantum phase transitions were studied in detail. Hubbard model compared to the traditional, extended Hubbard model considers the nearest neighbor interaction V. Calculated that, when the V / t is relatively small (V / t <4.2), the system has only one metal - insulator quantum phase transition point. As the V / t increases, the system respectively, three (4.2 8.4), the system becomes completely insulator. Through some of the critical point critical exponents v and z calculations, we found that due to neighbor interaction V / t the introduction of the system of critical exponents have also changed, which indicates that the V / t and U / t induced phase transitions different mechanisms. Generally believed, U / t will lead to the introduction of the system appear spin density wave (SDW), and V / t lead to the introduction of the charge density wave (CDW) generation. In order to characterize the two-phase competition, we also used the Hartree-Fock mean-field approach of the charge order (CO) and spin order (SO) in the U / tV / t phase diagram of the distribution. These phase transitions in the study of the process, apart from using the relevant order to describe various parameters of the phase curve, but also a single lattice point of entangled different parameters change in the region. The results show that a single grid entangled pairs U / t derivative of the metal - insulator transition boundary will appear extreme, and in the CDW and SDW phase transition boundary, a single grid point entanglement appeared jump. These results reveal a single grid point again entangled quantum phase transitions in the special role of the research process, which can use it to describe the different quantum phase transitions as a general order parameter.

Metal-insulator Transition on a Half Filled Triangular Lattice

Abstract

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