Large piezo-/flexo-electric and flexomagnetic effects in a semiconducting cobalt telluride monolayer

Engineering piezo-/flexo-electricity and flexomagnetism in two-dimensional (2D) materials beyond the best-known graphene and transition metal dichalcogenides has potential for accelerating micro- and nano-electromechanical system applications. Herein, using first-principles calculations, we demonstrate cobalt mono-telluride (CoTe) monolayer as an outstanding candidate for achieving large piezoelectric, flexoelectric and flexomagnetic responses down to the monolayer limit. The CoTe monolayer is found to be a semiconductor with a sizable bandgap of 0.48 eV, which is tunable using in-plane uniaxial or biaxial strains. This is because the puckered structure and intrinsic charge distribution asymmetry along the perpendicular direction enable the structure and properties to be heavily dependent on the external strain. In addition, the CoTe monolayer exhibits an out-of-plane polarization of up to ∼21 pC m^-1 with a flexoelectric coefficient of ∼0.08 nC m^-1 and a flexomagnetic coefficient of 89.59μ_B Å, surpassing most of the other 2D binary systems to the best of our knowledge. These findings not only clarify the fundamental structure and properties of the CoTe monolayer but also solidify the feasibility and designability of constructing piezo-/flexo-electric and flexomagnetic devices based on CoTe.