Strain-induced quantum phase transition in the C3Sc4 monolayer: towards multiple gapless fermions

Abstract

Most two dimensional (2D) topological materials host only one kind of fermionic state. However, realizing multiple gapless fermions in a single 2D material is rarely reported. Furthermore, researchers face challenges in regulating various gapless fermion transitions using specific methods. Herein, we perform a study based on the first-principles calculation to investigate the electronic structures and the related fermionic states of strained 2D C₃Sc₄. C₃Sc₄ is an ideal system in the ground state with twelve Dirac points. The dynamical, mechanical, and thermal stabilities of the proposed C₃Sc₄ monolayer are demonstrated in detail. Interestingly, under the condition of 9.5% biaxial tensile strain, gapless and quadratic Weyl fermionic states are observed at the Γ point. A gapless and massless pseudospin-1 fermion appears at the Γ point in the 2D C₃Sc₄ system under 13% biaxial tensile strain and with hole doping. The Fermi velocity of this massless pseudospin-1 fermion is 2.1 × 10⁵ m s⁻¹, comparable to that of well-known 2D gapless topological materials. The results indicate that 2D C₃Sc₄ is an ideal playground to explore interesting behaviors of quantum phase transitions and rich gapless fermionic states and also reveal its potential applications in high-speed nano-devices.