Nonperturbative Estimates of Electrical Current in 2D Dirac Systems - A MoS2 Example*

The term “Dirac materials” refers to a large set of seemingly-disparate materials which share many universal properties and may be described by the Dirac equation. The effect of external time-dependent fields on their carrier dynamics is of great importance. However, due to the non-commutativity of the Dirac Hamiltonian in time domain, non-perturbative estimates of the propagator of a Dirac spinor are challenging to obtain.
Here, we propose an approach to construct observables, through the use of a suitable Magnus expansion and, with it, study the effect of shining light and deforming the sample on the produced current of arbitrary chemical potential and temperature. These two processes are captured by the coupling of electromagnetic and valley-dependent pseudo-electromagnetic fields. For appropriate excitation regimes, we show how (a) both fields create currents and (b) how these two fields can undergo interference and create both electrical and valley current and charge densities.