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In the present work, the problem of an all-coupling analytic description for the optical conductivity of the Froehlich polaron is treated, with the goal being to bridge the gap in validity range that exists between two complementary methods: on the one hand the memory function formalism and on the other hand the strong-coupling expansion based on the Franck-Condon picture for the polaron response. At intermediate coupling, both methods were found to fail as they do not reproduce Diagrammatic Quantum Monte Carlo results. To resolve this, we modify the memory function formalism with respect to the Feynman-Hellwarth-Iddings-Platzman (FHIP) approach, in order to take into account a non-quadratic interaction in a model system for the polaron. The strong-coupling expansion is extended beyond the adiabatic approximation, by including into the treatment non-adiabatic transitions between excited polaron states. The polaron optical conductivity that we obtain by combining the two extended methods agree well, both qualitatively and quantitatively, with the Diagrammatic Quantum Monte Carlo results in the whole available range of the electron-phonon coupling strength.
Exact results for the density of states and the ac conductivity of the spinless Holstein model at finite carrier density are obtained combining Lanczos and kernel polynomial methods.
The polaron optical conductivity is derived within the strong-coupling expansion, which is asymptotically exact in the strong-coupling limit. The polaron optical conductivity band is provided by the multiphonon optical transitions. The polaron optica
We investigate the origin of quantum geometric phases, gauge fields and forces beyond the adiabatic regime. In particular, we extend the notions of geometric magnetic and electric forces discovered in studies of the Born-Oppenheimer approximation to
We investigate the origin of quantum geometric phases, gauge fields and forces beyond the adiabatic regime. In particular, we extend the notions of geometric magnetic and electric forces discovered in studies of the Born-Oppenheimer approximation to
We examine ground state correlations for repulsive, quasi one-dimensional bosons in a harmonic trap. In particular, we focus on the few particle limit N=2,3,4,..., where exact numerical solutions of the many particle Schroedinger equation are availab