Electron States of Solids Division, Faculty of Physics, Adam Mickiewicz University in Poznań, Poznań, Poland.
J Phys Condens Matter. 2013 Feb 13;25(6):065603. doi: 10.1088/0953-8984/25/6/065603.
We have studied the extended Hubbard model with pair hopping in the atomic limit for arbitrary electron density and chemical potential and focus on paramagnetic effects of the external magnetic field. The Hamiltonian considered consists of (i) the effective on-site interaction U and (ii) the intersite charge exchange interactions I, determining the hopping of electron pairs between nearest-neighbour sites. The phase diagrams and thermodynamic properties of this model have been determined within the variational approach (VA), which treats the on-site interaction term exactly and the intersite interactions within the mean-field approximation. Our investigation of the general case shows that the system can exhibit not only the homogeneous phases-superconducting (SS) and non-ordered (NO)-but also the phase separated states (PS: SS-NO). Depending on the values of interaction parameters, the PS state can occur in higher fields than the SS phase (field induced PS). Some ground state results beyond the VA are also presented.
我们研究了任意电子密度和化学势下原子极限的扩展 Hubbard 模型，并关注外磁场的顺磁效应。所考虑的哈密顿量由（i）有效局域相互作用 U 和（ii）确定电子对在最近邻站点之间跃迁的站点间电荷交换相互作用 I 组成。该模型的相图和热力学性质已通过变分方法（VA）确定，VA 精确处理局域相互作用项，平均场近似处理站点间相互作用项。我们对一般情况的研究表明，该系统不仅可以表现出均匀相（超导（SS）和无序（NO）），还可以表现出相分离状态（PS：SS-NO）。根据相互作用参数的值，PS 状态可能出现在高于 SS 相的磁场中（磁场诱导 PS）。还给出了 VA 之外的一些基态结果。
