Can the Boltzmann-tryanny be overcome via topological field effect switching? - insignts into mechanisms and fundamental limits*

Electric field-driven topological phase transitions in quantum spin Hall (QSH) materials with buckled honeycomb lattice in the presence of Rashba spin-orbit interactions are considered to be an interesting playground for implementing Topological Quantum Field-Effect Transistors (TQFETs). However, defying the wisdom  in conventional transistors being ideally limited to 60mV/decade, we demonstrate that for a topological transistor the thermionic limit of subthreshold slope is actually twice as much.  Also, by employing the non-equilibrium Green's function (NEGF) approach, we demonstrate that the mere introduction of Rashba interaction [1] does not help to reduce the subthreshold swing. As a probable solution, we propose that the introduction of anti-ferromagnetic exchange interaction, enabling a transition between the quantum spin valley Hall (QSVH) phase and the quantum anomalous Hall (QAH) phase, can help us go past not only the 120mV/decade limit but also the 60mV/decade limit for an appropriately chosen set of parameters.