MXene with Janus Structure at Transition metal site -A route to Emergent Properties

Abstract

Motivated by the discovery of bimetallic MXene compounds with Janus metal sites, we investigate Janus MXenes TiM"CO2, where M" = Mo, W. Our computational analysis reveals that broken inversion symmetry in the Janus structure, coupled with strong spin-orbit coupling at M", generates diverse and remarkable functionalities. These include pronounced Rashba spin splitting, non-trivial Z2 topology, Berry-curvature-dipole-driven nonlinear anomalous Hall effect, and strain control of the Berry curvature dipole. Notably, the 4d transition-metal-based TiMoCO2 and 5d transition-metal-based TiWCO2, with M" elements from the same column of the periodic table, display markedly different behaviors. While TiMoCO2 is a Z2 topological insulator, TiWCO2 is a trivial semimetal. Both compounds, however, exhibit compelling quantum properties. TiWCO2 shows a robust Rashba effect with a large Rashba coefficient of 1.35 eV. Angstrom and a large nonlinear anomalous Hall conductivity of 120 x 0.0001 G0. TiMoCO2, a Z2 narrow-gap semiconductor with weaker Rashba splitting and moderate nonlinear anomalous Hall conductivity, exhibits a strain-driven transition from semiconductor to semimetal. This transition modulates both the sign and magnitude of the Berry curvature dipole, yielding a sizable nonlinear anomalous Hall conductivity of 17 X 0.0001 G0 under 2% tensile strain. Our findings underscore the potential of MXenes as a platform for investigating and tailoring multifunctional quantum phenomena.