Monolayer Mg2C: Negative Poisson's ratio and unconventional two-dimensional emergent fermions

ORAL

Abstract

Two-dimensional (2D) emergent fermions and negative Poisson's ratio in 2D materials are fascinating subjects of research. Here, we predict that the hexacoordinated Mg2C monolayer hosts both exotic properties. We analyze its phonon spectrum, reveal the Raman-active modes, and show that it has small in-plane stiffness constants. Particularly, the Mg2C monolayer shows an intrinsic negative Poisson's ratio ∼−0.023 along zigzag. The material is metallic at its equilibrium state. A moderate biaxial strain can induce a metal-semimetal-semiconductor phase transition, during which several types of 2D unconventional fermions emerge, including Dirac fermions, the 2D double Weyl fermions in the semimetal phase, and the 2D pseudospin-1 fermions around which three bands cross at a single point on the Fermi level. In addition, uniaxial strains along the high-symmetry directions break the threefold rotational symmetry and reduce the number of Dirac points. Interestingly, it also generates 2D type-II Dirac points. We construct effective models to characterize the properties of these fermions. Our result reveals Mg2C monolayer as an intriguing platform for the study of 2D unconventional fermions, and also suggests its great potential for nanoscale device applications.

Presenters

  • Shan-Shan Wang

    Singapore University of Technology and Design

Authors

  • Shan-Shan Wang

    Singapore University of Technology and Design

  • Shengyuan Yang

    Singapore University of Technology and Design, Engineering Product Development, Singapore University of Technology and Design, Science and Math, Singapore University of Technology and Design, Research Laboratory for Quantum Materials, Singapore University of Technology and Design