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Lifshitz phase transitions in the ferromagnetic regime of the Kondo lattice model

机译：Kondo晶格模型的铁磁状态下的Lifshitz相变

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摘要

We establish the low-temperature phase diagrams of the spin-1/2 and spin-1 Kondo lattice models as a function of the conduction-band filling n and the exchange coupling strength J in the regime of ferromagnetic effective exchange interactions (n apporx≤ 0.5, J/D apporx≤ 2). We show that both models have several distinct ferromagnetic phases separated by continuous Lifshitz transitions of the Fermi-pocket vanishing or emergence type: one of the phases has a true gap in the minority band (half metal with magnetization rigidity), the others only a pseudogap. The spin-1/2 model has the half-metal phase, two topologically different pseudogap phases, and a paramagnetic state for very large J. The spin-1 model has the half-metal phase and a single pseudogap phase with an electron pocket. We find that, quite generically, ferromagnetism and Kondo screening coexist rather than compete both in spin-1/2 and spin-1 models. We establish the hysteretic behavior of the systems in an external magnetic field: spin-flop transitions preempt further Lifshitz transitions at finite magnetic field. We establish a "ferromagnetic Doniach diagram": in the spin-1/2 model the Curie temperature peaks near J/D ≈ 1.2 and goes to zero, while in the spin-1 model it saturates.
机译：我们建立了自旋1/2和自旋1 Kondo晶格模型的低温相图，它们是在铁磁有效交换相互作用（n约等于≤n的范围内）与导带填充n和交换耦合强度J的函数0.5，J / D近似值≤2）。我们表明，两个模型都具有由费米口袋消失或出现类型的连续Lifshitz跃迁分隔的几个不同的铁磁相：其中一个相在少数能带中具有真实的间隙（具有磁化刚度的半金属），其他相仅是伪间隙。自旋1/2模型具有半金属相，两个拓扑上不同的拟能隙相以及非常大的J的顺磁态。自旋1模型具有半金属相和具有电子口袋的单个拟能隙相。我们发现，在一般情况下，铁磁性和近藤屏蔽共存，而不是在spin / 1/2和spin-1模型中竞争。我们在外部磁场中建立了系统的磁滞行为：自旋触发器跃迁在有限磁场处取代了进一步的Lifshitz跃迁。我们建立了一个“铁磁Doniach图”：在自旋1/2模型中，居里温度在J / D≈1.2附近达到峰值并趋于零，而在自旋1模型中则达到饱和。

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