Coexisting charge density wave and ferromagnetic instabilities in monolayer InSe

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.

Multi-band D-TRILEX approach to materials with strong electronic correlations

“…1. These expressions illustrate that in the D-TRILEX approach the single-and two-particle quantities are treated self-consistently, which allows one to account for the effect of collective electronic fluctuations onto the electronic spectral function and vice versa [94][95][96][97].…”

“…Importantly, as shown in Appendix A.2, the divergence in the lattice susceptibility X ς q occurs at the same time as in the renormalized interaction W ς q that enters the self-energy (18). This allows the D-TRILEX approach to capture the formation of the pseudogap in the electronic spectral function in the paramagnetic regime in the vicinity of a symmetry broken phase in the system [95,97].…”

“…Previous works on D-TRILEX [93][94][95] suggest that the method is able to account for the effect of the non-local interactions. However, no thorough benchmarking of the results for the extended Hubbard model has been performed so far.…”

“…Particular examples of such theories are the GW +DMFT [64][65][66][67][68][69][70], the dual fermion (DF) [71][72][73][74][75][76], the dual boson (DB) [77][78][79][80][81][82][83], the dynamical vertex approximation (DΓ A) [84][85][86][87][88], the triply irreducible local expansion (TRILEX) [89][90][91][92], and the dual TRILEX (D-TRILEX) [20,[93][94][95][96][97] methods. Among them, DF, DB, and DΓ A have the most sophisticated diagrammatic structures that allow for a very accurate description of both, local and non-local correlation effects [98].…”

Role of correlated hopping in the many-body physics of flat-band systems: Nagaoka ferromagnetism

“…Another example is a single layer of InSe where an almost flat hole band arises without any twisting. The appearance of this band is accompanied, among other things, by an anomalously strong electron-phonon interaction and closeness to ferromagnetic and charge-density-wave instabilities [11,12]. Strong correlation effects are thus practically unavoidable in narrow-band systems.…”