Measure of Diracness in two-dimensional semiconductors

We analyze the low-energy properties of two-dimensional direct-gap semiconductors, such as, for example, the transition-metal dichalcogenides MoS2, WS2, and their diselenide analogues MoSe2, WSe2, etc., which are currently intensively investigated. In general, their electrons have a mixed character —they can be massive Dirac fermions as well as simple Schrödinger particles. We propose a measure (Diracness) for the degree of mixing between the two characters and discuss how this quantity can in principle be extracted experimentally, within magneto-transport measurements, and numerically via ab initio calculations