Non-stoichiometry effects on the extreme magnetoresistance in Weyl semimetal WTe2

Non-stoichiometry effect on the extreme magnetoresistance is systematically investigated for the Weyl semimetal WTe2. Magnetoresistance and Hall resistivity are measured for the as-grown samples with a slight difference in Te vacancies and the annealed samples with increased Te vacancies. The fittings to a two-carrier model show that the magnetoresistance is strongly dependent on the residual resistivity ratio (i.e., the degree of non-stoichiometry), which is eventually understood in terms of electron doping which not only breaks the balance between electron-type and hole-type carrier densities but also reduces the average carrier mobility. Thus, compensation effect and ultrahigh mobility are probably the main driving force of the extreme magnetoresistance in WTe2.