Single-Spin Waved-Brim Flat-Top Hat in the Band Edge of GdIH Monolayer

TL;DR

This paper predicts a novel single-spin waved-brim flat-top hat electronic band in GdIH monolayer, which exhibits valley polarization and tunable conductive states, opening new avenues for valleytronics and spintronics in 2D materials.

Contribution

It introduces a general dispersion model for hat-like bands and identifies a unique waved-brim flat-top band in GdIH monolayer with potential for high-temperature valley Hall effects.

Findings

Discovery of a waved-brim flat-top band with six valleys.

Observation of spontaneous valley polarization due to symmetry breaking.

Potential for tunable conductive states via strain and doping.

Abstract

Exotic electronic bands, such as flat bands, linear crossing bands, spontaneously valley- or spin-polarized bands, in two-dimensional materials have been the hot topics in condensed matter physics. Herein, we first propose a general dispersion model for possible hat-like electronic bands, and then identify an intriguing single-spin \emph{waved-brim flat-top hat} in the valence band edge of a stable ferromagnetic semiconducting electrene (i.e., Janus GdIH monolayer), which can be well described by a simplified two-bands Hamiltonian model. Specifically, the hat-band has a waved brim with six valleys along the boundary of the first Brillouin zone; meanwhile it holds a flat top close to the Fermi level, resulting in the emergence of single-spin van Hove singularities divergence and Lifshitz transitions. Owing to the breaking of both time-reversal and space inversion symmetries, a sizable spontaneous valley polarization is formed between the adjacent brim valleys, which provides the opportunity to realize the high-temperature anomalous valley Hall effect. Particularly, via modest strains and carriers doping, various conductive bipolar-states (spin-up vs. spin-down, K valley vs. $-$K valley, and ultra-low-speed vs. ultra-high-speed) can be modulated out from the distorted waved-brim flat-top hat of GdIH ML.