来源：npj计算材料学
二维 III-VI 族金属硫属化物具有高电荷载流子迁移率、可控能隙、优异的热电和光学性能，以及在环境条件下的优异稳定性，是研究多体相关效应的潜在候选材料。但是到目前为止，基于密度泛函理论 (DFT)的计算都没有系统地考虑多体效应。
Fig. 2 Phase diagram for the monolayer InSe as a function of temperature and doping.
来自法国巴黎理工学院的Evgeny A. Stepanov 与其德国、荷兰的合作者解决了单层 InSe 中的集体电子效应问题，他们同时考虑了长程库仑相互作用和电子 - 声子耦合效应，并推导出了一个现实的模型，该方法明确考虑了非局部集体电子波动。结果表明，单层 InSe 可以作为研究共存的多体相关效应，特别是二维磁性的有吸引力的研究体系，尽管在体相中这种材料是非磁性的。更重要的是，由于电子系统中库仑驱动的 CDW 不稳定性表现为局部和非局部电子-电子相互作用之间的竞争，这种相互作用有利于晶格上电子的不同分布。为了改变这些相互作用之间的平衡，这里考虑的独立 InSe 单层可以暴露于外部介电屏蔽，例如，由基板或封装产生。
Fig. 3 Momentum resolved susceptibilities Xς q;ω calculated at zero frequency ω = 0 in the absence of the electron–phonon coupling.
这种机制在二维材料中特别有效，因为环境筛选在层状材料中是非局域的，这减少了比现场相互作用更强的远程相互作用。这种库仑工程为探索额外的自由度并调整这种二维材料中的相关效应铺平了道路。该文近期发布于npj Computational Materials 8: 118 (2022)。手机阅读原文，请点击本文底部左下角“阅读原文”，进入后亦可下载全文PDF文件。
Editorial Summary
Two-dimensional III-VI metal chalcogenides have high charge carrier mobility, controllable energy gap, excellent thermoelectric and optical properties, and excellent stability under environmental conditions. They are potential candidates for studying multi-body correlation effects. But so far, the calculation based on density functional theory (DFT) has not systematically considered the multi-body effect.
Fig. 5 Momentum resolved charge susceptibility Xc(q, ω = 0).
Evgeny A. Stepanov from CPHT, CNRS, Ecole Polytechnique, Institut Polytechnique de Paris and his collaborators from Germany and Netherlands solved the collective electron effect in single-layer InSe. They also considered the long-range Coulomb interaction and electron phonon coupling effect, and deduced a realistic model, which explicitly considered the nonlocal collective electron fluctuation. The results show that single-layer InSe can be used as an attractive research system to study the multi-body correlation effects of coexistence, especially two-dimensional magnetism, although this material is non-magnetic in the bulk phase. More importantly, since the Coulomb driven CDW instability in the electronic system is manifested as the competition between local and non local electron electron interactions, this interaction is conducive to the different distribution of electrons on the lattice. In order to change the balance between these interactions, the independent InSe monolayer considered here may be exposed to an external dielectric shield, for example, generated by a substrate or encapsulation.
Fig. 6 Momentum resolved charge susceptibility Xc (q) calculated at zero frequency ω = 0.
This mechanism is particularly effective in two-dimensional materials because environmental screening is nonlocal in layered materials, which reduces remote interactions that are stronger than in-situ interactions. This Coulomb engineering paves the way for exploring additional degrees of freedom and adjusting the correlation effects in this two-dimensional material. This article was recently published in npj computational materials 8: 118 (2022).
Fig. 7 Momentum resolved spin susceptibility Xs(q) calculated at zero frequency ω = 0 taking into account the electron–phonon coupling.
原文Abstract及其翻译
Coexisting charge density wave and ferromagnetic instabilities in monolayer InSe (单层 InSe 中共存的电荷密度波和铁磁不稳定性)
Evgeny A. Stepanov, Viktor Harkov, Malte Rösner, Alexander I. Lichtenstein, Mikhail I. Katsnelson & Alexander N. Rudenko
Abstract Recently fabricated InSe monolayers exhibit remarkable characteristics that indicate the potential of this material to host a number of many-body phenomena. In this work, we systematically describe collective electronic effects in hole-doped InSe monolayers using advanced many-body techniques. To this end, we derive a realistic electronic-structure model from first principles that takes into account the most important characteristics of this material, including a flat band with prominent van Hove singularities in the electronic spectrum, strong electron–phonon coupling, and weakly screened long-ranged Coulomb interactions. We calculate the temperature-dependent phase diagram as a function of band filling and observe that this system is in a regime with coexisting charge density wave and ferromagnetic instabilities that are driven by strong electronic Coulomb correlations. This regime can be achieved at realistic doping levels and high enough temperatures, and can be verified experimentally. We find that the electron–phonon interaction does not play a crucial role in these effects, effectively suppressing the local Coulomb interaction without changing the qualitative physical picture.
摘要最近构造的单层 InSe 结构表现出显著的特性，从而表明这种材料拥有多种多体效应的潜力。在本工作中，我们使用先进的多体技术系统地描述了空穴掺杂 InSe 单层中的集体电子效应。为此，我们从第一性原理推导出了一个现实的电子结构模型，该模型考虑了该材料最重要的特性，包括电子光谱中具有显着范霍夫奇点的平带、强电子-声子耦合和弱屏蔽长程库仑相互作用。我们将温度相关相图计算作为带填充的函数，并观察到该系统处于由强电子库仑相关驱动的电荷密度波和铁磁不稳定性并存的状态中。这种体系可以在实际的掺杂水平和足够高的温度下实现，并且可以通过实验验证。我们发现电子-声子相互作用在这些效应中没有发挥关键作用，在不改变定性物理图像的前提下有效地抑制了局部库仑相互作用。
Fig. 10 Phonon properties from first-principle calculations.