tailieunhanh - Conductivity in half-filled ionic hubbard model

We calculate the temperature dependent conductivity in the half-filled ionic Hubbard model with an on-site Coulomb repulsion U and an ionic energy ∆ by mean of the coherent potential approximation. It is shown that for intermediate and large ∆ the largest conductivity occurs near the special value U = 2∆ at all temperatures T , for a fixed ∆ the region of finite conductivity [Uc1,Uc2] expands and its maximum decreases with increasing T . Our results are in good agreement with those derived from the determinant quantum Monte Carlo simulation. | Communications in Physics, Vol. 24, No. 3S2 (2014), pp. 18-22 DOI: CONDUCTIVITY IN HALF-FILLED IONIC HUBBARD MODEL NGUYEN DANH TUNG AND HOANG ANH TUAN Institute of Physics, Vietnam Academy of Science and Technology E-mail: hatuan@ Received 20 June 2014 Accepted for publication 20 August 2014 Abstract. We calculate the temperature dependent conductivity in the half-filled ionic Hubbard model with an on-site Coulomb repulsion U and an ionic energy ∆ by mean of the coherent potential approximation. It is shown that for intermediate and large ∆ the largest conductivity occurs near the special value U = 2∆ at all temperatures T , for a fixed ∆ the region of finite conductivity [Uc1 ,Uc2 ] expands and its maximum decreases with increasing T . Our results are in good agreement with those derived from the determinant quantum Monte Carlo simulation. Keywords: static conductivity, ionic Hubbard model, coherent potential approximation. I. INTRODUCTION It is well established that an on-site Coulomb interaction between the valence electrons with opposite spins can lead to their localization in the lattice sites and can drive a transition to a chargegapped Mott insulator (MI). On the other hand, the imposition of an external periodic potential can drive a band insulator (BI) with one sub-band fully filled and the other one empty. The ionic Hubbard model (IHM) includes an on-site Coulomb repulsion and a staggered potential and is therefore well suited to study transitions between metallic and different insulating phases [1, 2]. Recently, the IHM in high dimensions has attracted much interest and it has been widely studied by a variety of techniques including Hartree-Fock theory, slave boson approach, determinant quantum Monte Carlo (DQMC) simulation, and dynamical mean field theory (DMFT) [3-9]. However, the precise conclusions about the phase diagram are still subject to some debate. In a previous paper [10] we have applied the .