Enhanced thermoelectric properties of two-dimensional Janus ferromagnetic LaBrI with strain-induced valley degeneracy

Abstract: Since the successful synthesis of the MoSSe monolayer, which violated the out-of-plane mirror symmetry of TMDs monolayers, considerable and systematic research has been conducted on Janus monolayer materials. By systematically analyzing the LaBrI monolayer, we are able to learn more about the novel Janus material by focusing on the halogen family next to group VIA (S, Se, Te). The structural optimizations have been carried out using pseudopotential based Quantum espresso code. Computed structural parameters are in good agreement with literature reports. The optimized crystal structures were used for computing effect of strain on electronic and thermoelectric properties. Dynamical stability predicts that this material can withstand up to 10% of tensile strain. Computed electronic structure reveals material to be indirect wide band gap ferromagnet with magnetic moment 1{\mu}B. With increase in the biaxial tensile strain the band gap decreases. Furthermore, the computed magneto-thermoelectric properties predict high Seebeck coefficient ~ 400 {\mu}V/K and low thermal conductivity of ~ 0.93 W/m.K in LaBrI which results in a high ZT ~ 1.84 for 4% strain at 800 K. The present study supports the fact that tensile strain on ferromagnetic LaBrI material can further enhance TE properties making it to be a promising material for TE applications at higher temperatures.