Controlled Spin Transport in Planar Systems Through Topological Exciton

It is shown that a charge-neutral spin-1 exciton, realizable only in planar systems like graphene, can effectively be used for controlled spin transport in such media. The excitonic bound state is destabilized by quantum fluctuations, characterized by a threshold for excitation and melts in a smooth manner under thermal fluctuations. This planar exciton differs from the conventional ones, as it owes its existence to the topological Chern-Simons (CS) term. The parity and time-reversal violating CS term can arise from quantum effects in systems with parity-breaking mass-gap. The spinning exciton naturally couples to magnetic field, leading to the possibility of controlled spin transport. Being neutral, it is immune to adverse effects, afflicting spin transport by charged fermions.