In this paper, we study a form of the Holstein molecular crystal model in which the influence of lattice vibrations on the transfers of electronic excitations between neighboring sites (off-diagonal coupling) is taken into account. Using the Toyozawa Ansatz and the Lanczos algorithm, the Holstein Hamiltonian with two types of off-diagonal coupling is studied focusing on a number of analyticity ...

We present measurements of spin transport in ultracold gases of fermionic 6Li in a mixture of two spin states at a Feshbach resonance. In particular, we study the spin-dipole mode, where the two spin components are displaced from each other against a harmonic restoring force. We prepare a highly imbalanced, or polaronic, spin mixture with a spin-dipole excitation and we observe strong, unitarit...

A self-consistent many-body theory of polarons is presented. This unifies weak- and strong-coupling approaches to the electron-phonon interaction from first principles, opening door toward a full characterization polaronic effects in materials at all coupling strengths.

Density-functional theory within a Berry-phase formulation of the dynamical polarization is used to determine second-order susceptibility $\chi^{(2)}$ lithium niobate (LiNbO$_3$). Defect trapped polarons and bipolarons are found strongly enhance nonlinear material, in particular if localized at Nb$_\mathrm{V}$-V$_{\mathrm{Li}}$ defect pairs. This essentially consequence polaronic excitation res...