Tetragonal Mexican-Hat Dispersion and Switchable Half-Metal State with Multiple Anisotropic Weyl Fermions in Penta-Graphene

TL;DR

This paper demonstrates that penta-graphene can exhibit inherent ferromagnetism and host multiple anisotropic Weyl fermions, enabling switchable spin states and diverse Weyl phenomena through doping and strain, advancing carbon-based spintronics.

Contribution

It reveals inherent ferromagnetism in penta-graphene and shows how to realize switchable half-metallicity and multiple Weyl states via doping and strain.

Findings

Inherent ferromagnetism in penta-graphene due to Mexican-hat band edge.

Switchable half-metallicity with room temperature stability.

Presence of multiple anisotropic Weyl fermions in strained, doped penta-graphene.

Abstract

In past decades, the ever-expanding library of 2D carbon allotropes has yielded a broad range of exotic properties for the future carbon-based electronics. However, the known allotropes are all intrinsic nonmagnetic due to the paired valence electrons configuration. Based on the reported 2D carbon structure database and first-principles calculations, herein we demonstrate that inherent ferromagnetism can be obtained in the prominent allotrope, penta-graphene, which has an unique Mexican-hat valence band edge, giving rise to van Hove singularities and electronic instability. Induced by modest hole-doping, being achievable in electrolyte gate, the semiconducting pentagraphene can transform into different ferromagnetic half-metals with room temperature stability and switchable spin directions. In particular, multiple anisotropic Weyl states, including type-I and type-II Weyl cones and hybrid quasi Weyl nodal loop, can be found in a sizable energy window of spin-down half-metal under proper strains. These findings not only identify a promising carbon allotrope to obtain the inherent magnetism for carbon-based spintronic devices, but highlight the possibility to realize different Weyl states by combining the electronic and mechanical means as well.