Strain effect on electronic structure and transport properties of zigzag α-T 3 nanoribbons: a mean-field theoretical study

Abstract

The α-T 3 lattice, a minimal model that presents flat bands, has sparked much interest in research but the finite-size effect and interaction has been rarely involved. Here we theoretically study the electronic structure and transport properties of zigzag-edge α-T 3 nanoribbons (ZαT 3NRs) with and without uniaxial strain, where the exemplary widths N = 40 and 41 for two series are considered. By adopting the mean-field Hubbard model combined with the nonequilibrium Green’s function method, we show that the spin-degenerate dispersionless flat band at the Fermi energy for the pristine ribbons is split into spin-up and -down flat bands under electron–electron Coulomb interaction. Specifically, the two bands are shifted toward in an opposite direction and away from the Fermi energy, which leads to an energy gap opening in the case of α ≠ 1. All three series of ZαT 3NRs with width N = 3n, 3n + 1, 3n + 2 (where n is a positive integer) exhibit an energy gap. This differs from the simple tight-binding calculations without considering electron–electron Coulomb interaction, for which the gap is always zero in the case of N = 3n + 1. Here, the origin of the energy gap for N = 3n + 1 arises from Coulomb repulsion between electrons. Importantly, the energy gap can be effectively manipulated by an uniaxial strain and Coulomb interaction if α ≠ 1. The gap linearly increases (decreases) when a tensile (compressive) strain increases, and it also monotonously increases as enhancing Coulomb interaction. Interestingly, a ground state of antiferromagnetic to ferromagnetic transition occurs when α increases from 0.8 to 1, leading to a semiconductor to metallic transition. Besides, the α-, strain- and interaction-dependent conductance is also explored. The findings here may be of importance in the band gap engineering and electromechanical applications of α-T 3 nanoribbon-based devices.