Frost research group

The Feynman path-integral variational solution to the polaron problem }cite{Feynman1955}, along with the associated FHIP linear-response mobility theory }cite{Feynman1962}, provides a computationally amenable method to predict the frequency-resolved temperature-dependent charge-carrier mobility, and other experimental observables in polar semi-conductors. We show that the FHIP mobility theory is capable of demonstrating non-Drude transport behaviour, and provides good agreement with the recent diagrammatic Monte-Carlo mobility simulations of Mishchenko et al. }cite{Mishchenko2019} for the abstract Fr}"ohlich Hamiltonian. We extend this method to multiple variational parameters in the model action, and to multiple phonon modes in the true action. This enables a slightly better variational solution, as inferred from the resulting energy. We carry forward this complexity into the mobility theory, where it enables richer structure in the frequency and temperature dependent mobility, due to the different phonon modes activating at different energies.