Abstract
Using density functional theory calculations, we study the electronic and magnetic properties of the p-type monolayer II-VI semiconductors SrX (X = S,Se). The pristine SrS and SrSe monolayers are large band gap semiconductor with a very flat band in the top valence band. Upon injecting hole uniformly, ferromagnetism emerges in those system in a large range of hole density. By varying hole density, the systems also show complicated phases transition among nonmagnetic semiconductor, half metal, magnetic semiconductor, and nonmagnetic metal. Furthermore, after introducing p-type dopants in SrS and SrSe via substitutionary inserting P (or As) dopants at the S (or Se) sites, local magnetic moments are formed around the substitutional sites. The local magnetic moments are stable with the ferromagnetic order with appreciable Curie temperature. The ferromagnetism originates from the instability of the electronic states in SrS and SrSe with the large density of states at the valence band edge, which demonstrates a useful strategy for realizing the ferromagnetism in the two dimensional semiconductors.
Highlights
Are lattice vectors, d is the shortest bond length between two types of atoms. (b) Side view of SrX, where the group II and the group VI atomic are located in the same plane without bucking, just like graphene. (c) Phonon dispersion curves of SrS monolayer
Our calculations are performed within density functional theory (DFT) using the projector augmented wave (PAW) potentials[34,35] and a plane-wave basis set, as implemented in Vienna ab initio simulation package (VASP)[36,37]
The large density of states (DOS) near the valence band edge would lead to instabilities to different phases, such as ferromagnetism, superconductivity, and charge density wave[41,42,43]
Summary
Are lattice vectors, d is the shortest bond length between two types of atoms. (b) Side view of SrX, where the group II and the group VI atomic are located in the same plane without bucking, just like graphene. (c) Phonon dispersion curves of SrS monolayer. The band structures of SrS and SrSe monolayers from PBE calculations are shown in Fig. 2(a) and (b), respectively. Pristine SrS and SrSe monolayers are nonmagnetic, our spin-polarized calculations show that those systems spontaneously develop a ferromagnetic ground state with some amount of hole doping.
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