Electric- and exchange-field controlled transport through silicene barriers: Conductance gap and near-perfect spin polarization

We study ballistic electron transport through silicene barriers, of width d and height U, in the presence of an exchange field M and a normal electric field E-z. Away from the Dirac point (DP), the spin- and valley-resolved conductances, as functions of U, exhibit resonances while close to it there is a pronounced dip that can be transformed into a transport gap by varying E-z. The charge conductance g(c) changes from oscillatory to a monotonically decreasing function of d beyond a critical E-z and this can be used to realize electric-field-controlled switching. Further, the field M splits each resonance of gc into two spin-resolved peaks. The spin polarization near the DP increases with E-z or M and becomes nearly perfect above certain of their values. Similar results hold for double barriers. (C) 2014 AIP Publishing LLC.