  A topological quantum field effect transistor (TQFET) uses electric field to
switch a material from topological insulator ("on", with conducting edge
states) to a conventional insulator ("off"), and can have low subthreshold
swing due to strong Rashba spin-orbit interaction. Numerous materials have been
proposed, and electric field switching has been demonstrated in ultrathin
Na${_3}$Bi. Here we propose a negative capacitance (NC) TQFET which uses a
ferroelectric to amplify the electric field and potentially achieve very low
switching voltages and energies. Materials challenges for realizing the
NC-TQFET are discussed.
