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Acta Physica Sinica

INSULATOR-METAL TRANSITION OF THE THE 2- D HALF- FILLED HUBBARD MODEL AT FI- NITE- TEMPERATURES

Ing H

Published Jan 1, 1994• 0 citations
OpenAlex

Abstract

In the present paper,we attempt to attack the problem of the existence of insu- 1ator- metal transition at finite temperature for a 2 dimensional half- filled Hubbard half- filled model.we used the grand Canonical quantum Monte Carlo method to ca- culate the electrical conductivity and the specific heat of the system. A peak on the specific heat vs temperature curve in high temperature region is observed,and the electrical conductivity curves show a sudden rise in the same temperature region. Thus.our results support that there exists a transition.

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INSULATOR-METAL TRANSITION OF THE 2-D HALF-FILLED HUBBARD MODEL AT FINITE-TEMPERATURES

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摘要 二维半充满条件下的Ｈｕｂｂａｒｄ模型，在有限温度下，是否经历一绝缘体—金属相变？在现有的文献中，这一直是一个有争议而又重要的问题。本文采用巨正则量子Ｍｏｎｔｅ Ｃａｒｌｏ方法，计算了二维半充满条件下Ｈｕｂｂａｒｄ模型的比热和电导率。对不同的库仑排斥势Ｕ（２ｔ－８ｔ），比热曲线在高温区出现一个峰，同时电导率在相应温区呈现一突然上升。因此，计算结果支持存在这样一个相变。 Abstract In the present paper, we attempt to attack the problem of the existence of insulator-metal transition at finite temperature for a 2 dimensional half-filled Hubbard half-filled model. we used the grand Canonical quantum Monte Carlo method to caculate the electrical conductivity and the specific heac of the system. A peak on the specific heat vs temperature curve in high temperature region is observed, and the electrical conductivity curves show a sudden rise in the same temperature region. Thus, our results support that there exists a transition. 作者及机构信息 陈锋, 应和平, 徐铁锋, 李文铸 1. 浙江大学物理系 基金项目: 国家自然科学基金及浙江省自然科学基金资助的课题. Authors and contacts CHHN FENG, YING HE-PING, XU TIE-FENG, LI WEN-ZHU 1. 浙江大学物理系 参考文献 施引文献

Acta Physica Sinica•Jan 1, 1994•0 citations

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arXiv:cond-mat/9612132•Physical review. B, Condensed matter•May 15, 1997•60 citations
In the present paper,we attempt to attack the problem of the existence of insu- 1ator- metal transition at finite temperature for a 2 dimensional half- filled Hubbard half- filled model.we used the grand Canonical quantum Monte Carlo method to ca- culate the electrical conductivity and the specific heat of the system. A peak on the specific heat vs temperature curve in high temperature region is observed,and the electrical conductivity curves show a sudden rise in the same temperature region. Thus.our results support that there exists a transition.
摘要 二维半充满条件下的Ｈｕｂｂａｒｄ模型，在有限温度下，是否经历一绝缘体—金属相变？在现有的文献中，这一直是一个有争议而又重要的问题。本文采用巨正则量子Ｍｏｎｔｅ Ｃａｒｌｏ方法，计算了二维半充满条件下Ｈｕｂｂａｒｄ模型的比热和电导率。对不同的库仑排斥势Ｕ（２ｔ－８ｔ），比热曲线在高温区出现一个峰，同时电导率在相应温区呈现一突然上升。因此，计算结果支持存在这样一个相变。 Abstract In the present paper, we attempt to attack the problem of the existence of insulator-metal transition at finite temperature for a 2 dimensional half-filled Hubbard half-filled model. we used the grand Canonical quantum Monte Carlo method to caculate the electrical conductivity and the specific heac of the system. A peak on the specific heat vs temperature curve in high temperature region is observed, and the electrical conductivity curves show a sudden rise in the same temperature region. Thus, our results support that there exists a transition. 作者及机构信息 陈锋, 应和平, 徐铁锋, 李文铸 1. 浙江大学物理系 基金项目: 国家自然科学基金及浙江省自然科学基金资助的课题. Authors and contacts CHHN FENG, YING HE-PING, XU TIE-FENG, LI WEN-ZHU 1. 浙江大学物理系 参考文献 施引文献
The Quantum Monte-Carlo simulations of the two-dimensional Hubbard model are presented for the half filling. The method based on the direct-space proposed by Suzuki and al., and Hirsch and al. was used. The states generated by this method are basis states in occupation number representation built with Wannier states localised on each site of the square array. The configurations of fermions can be observed on the real 2D array. An antiferromagnetic factor is defined and calculated for each temperature. The curves of energy, specific heat, conducivity and antiferromagnetic factor are presented for different values of the repulsive coulombian on site interaction U. There is a metal-insulator transition at low temperature for small values of U. This transition corresponds with a paramagnetic-ferromagnetic first order transition. Indeed, for these interaction values, the energy curves show a gap which is a characteristic of a first order transition. An hysteresis phenomenon appears on the conductivity curves. There is a behaviour change for U/t=3.5. For the values U>3.5 there is ferromagnetic-paramagnetic change without observable effect on the energy and the specific heat. The metal-insulator transition does not exist any more, the conductivity stays very small. Isotherms of the physical quantities versus U/t show a transition which seems to be the metal-insulator Mott transition. These results allow to draw a phase diagram with two first order transition lines.
We study the metal-insulator transition of the d-dimensional Hubbard model by treating the hopping term between adjacent 1-d chains in the frame of a Clifford linearization scheme, and keeping the full model along the chains. A general equation for the critical point is worked out in terms of the correlation functions of the one-dimensional model, assuming that the transition is of the second order. The equation, which holds at any temperature, is here investigated especially at T=0, where the latter condition holds true. The solution shows the existence of an insulating ground state in any d only at half-filling for U strictly positive, as in the exact 1-d case. The transition is found to be related to a parameter reminiscent of entropy.
Quantum Monte Carlo results for the specific heat c of the two-dimensional Hubbard model are presented. At half filling it was observed that c\ensuremath{\sim}T2{\mathrm{T}}^{2}T2 at very low-temperatures. Two distinct features were also identified: a low-temperature peak related to the spin degrees of freedom and a higher-temperature broad peak related to the charge degrees of freedom. Away from half filling the spin-induced feature slowly disappears as a function of hole doping while the charge feature moves to lower temperature. A comparison with experimental results for the high-temperature cuprates is discussed.