Effect of spin–orbit interaction on the electronic and optical properties of ultrathin bismuthnanowires—a density functional approach

Abstract

A first-principles study of the effects of spin–orbit coupling (SOI) on thestructural, electronic and optical properties of 16 bismuth nanowires,Bin with n = 7–18, has been performed. The density functional theory (DFT) in the local densityapproximation (LDA) has been used. The inclusion of the SOI significantly altersthe electronic and optical properties of the wires. The stable structures for theBin wireswith n = 7–18 form two groups: non-helical and helical configurations. In addition to the most stablenon-helical 5-Bi pentagonal, 6-Bi hexagonal and 6-Bi triple-zigzag wire configurationsfound in a previous report, the present study adds to this list three more non-helicalstructures, namely the non-helical 7-Bi hexagonal, 8-Bi heptagonal and 11-Bi pentagonalcross-sectional wire configurations. The present result is in sharp contrast to theconclusions of our previous studies of Pb- and Tl-nanowires, where it was observed that, ingeneral, a structure possessing a high coordination number value has large binding energyand, therefore, the helical wire structures are the most stable ones. All of the wires aremetallic in the LDA. The number of channels in the nanowires is large which will lead tohigh quantum ballistic conduction. The consideration of the many body effects such as theGW approximation (GWA) may destroy the metallicity predicted here in theBin wireconfigurations for n≤7. However, for the wire configurations havingn≥8, we find that even in the GWA, one may not observe the opening of the energy gapsbecause of the violation of the electron counting principle.The optical absorption calculated with SOI is much stronger compared to the one obtainedafter neglecting the SOI. For the wires containing a large number of atoms in the unit cell,the optical absorption is multi-peaked, strong and extended over the whole energyregion from infrared to the ultraviolet electromagnetic radiation including thevisible region. These nanowires may thus be used as a source of white radiation.