Prediction of van Hove singularities, excellent thermoelectric performance, and non-trivial topology in monolayer rhenium dichalcogenides

Abstract

Two-dimensional (2D) thermoelectric materials are gaining more intense attention with the ever-increasing global demand for energy. Recently, the search for compounds exhibiting excellent thermoelectric and topological characteristics has also attracted research exploration. In this study, a systematic investigation of Re-based transition metal dichalcogenides (TMDs) (ReX2, X = S, Se, and Te) through first-principles calculations identified the stability and electronic properties of the 1Tdp (1T double prime), 1T′, 1T, and 2H phases for the pristine bulk and monolayer ReX2. Formation energy and phonon dispersion calculations showed that the bulk and monolayer structures are only stable in the 1Tdp structure. The calculated bandgaps of bulk under the hybrid functional approach are 1.567 eV, 1.429 eV, and 0.745 eV, while those of the monolayer phases are 1.902 eV, 1.658 eV, and 1.323 eV for ReS2, ReSe2, and ReTe2, respectively. Moreover, van Hove singularities (vHss) are observed in monolayer ReX2 suggesting possible superconductivity. Remarkably, the calculated figure of merits (ZT) of bulk and monolayer ReX2 with values up to 2.30 presents them as excellent materials for thermoelectric (TE) applications since good TE materials have ZT > 0.40. In addition, the effect of one- (1h) and two-sided (2h) hydrogenation on the structural, electronic, magnetic, and topological properties of monolayer ReX2 were also investigated. Two-sided hydrogenation caused a stable structural phase transition from 1Tdp to 1T. A ferromagnetic phase transition was also observed upon the two-sided hydrogenation of ReS2 (2h-ReS2) and the one-sided hydrogenation of ReSe2 (1h-ReSe2). Finally, one-sided hydrogenation of monolayer ReSe2 and ReTe2 (1h-ReSe2 and 1h-ReTe2) resulted in non-trivial topological phases as confirmed by the calculated Z2 and Chern topological invariant numbers. Our findings show that the 2D Re-based TMDs exhibit highly tunable properties which have the potential for thermoelectric and spintronics applications.