Abstract

The magnetic molecular conductor λ-(BETS)₂FeCl₄ shows metal–insulator (MI) transition and antiferromagnetic (AF) transition simultaneously at T_MI ~ 8.3 K. In its metallic phase, two Fermi surfaces coexist, and the one has good nesting, and the other has bad nesting. Although a scenario of the MI transition by the formation and stabilization of a spin-density-wave (SDW) AF order is likely, it is not straightforward due to the existence of the bad nesting Fermi surface. In this paper, we propose a novel mechanism for the MI transition motivated by this material. Our proposal is based on the square-lattice two-band t − t^′− U Hubbard model at half-filling, and we examine this mechanism in the ground state. As the key part of our mechanism, we incorporate the interband exchange interaction between the band A with good nesting Fermi surface and the band B with bad nesting Fermi surface. We analyze B, incorporating the electronic correlation effect into the quasi-particle weight by the slave-rotor approach. In this model, as the value of U∕t increases, the SDW state in A induces another SDW state in B via the interband exchange interaction. As a result, this exchange interaction significantly decreases the value of U∕t required for the MI transition.

Graphical abstract

中文翻译：

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两频带Hubbard模型中自旋密度波诱导的金属-绝缘体跃迁在磁性分子导体λ-（BETS）2 FeCl 4中的应用

摘要

磁性分子导体λ-（BETS）₂ FeCl ₄在T _MI〜8.3 K时同时显示出金属-绝缘体（MI）转变和反铁磁（AF）转变。在其金属相中，两个费米表面共存，其中一个具有良好的嵌套，而另一个嵌套不好。尽管可能通过自旋密度波（SDW）AF阶的形成和稳定来发生MI跃迁，但由于存在不良的嵌套费米表面，这种情况并不简单。在本文中，我们提出了一种由这种材料激发的MI转变的新机制。我们的建议是基于正方形格子两带牛逼-牛逼^' - üHubbard模型处于半填充状态，我们在基态下研究了这种机制。由于我们的机制的重要组成部分，我们结合了带之间的带间交换作用一个良好的筑巢费米面和乐队乙不良嵌套费米面。我们分析B，通过从转子方法将电子相关效应纳入准粒子权重。在该模型中，随着U ∕ t值的增加，A中的SDW状态通过带间交换交互作用在B中诱导另一个SDW状态。结果，这种交换相互作用大大降低了U ∕ t的值。 MI过渡所需。

图形概要