THE PROPERTIES OF NONADIABATIC FLUCTUATIONS IN STRONGLY COUPLED ELECTRON–PHONON SYSTEMS WITH CORRELATED DISPLACEMENT AND SQUEEZING

A new variational ansatz for the coherent phonons with correlated displacement and squeezing, including interaction with electrons are used to study the properties of (i) the nonadiabatic phonon fluctuation on the ground state, (ii) the uncertainty principle, (iii) the phonon-staggered ordering, and (iiv) the charge-density wave order, of the systems due to fluctuations of the electron density in a coupled electron–phonon systems. The results obtained show that the correlation effect can lower the energy of the ground state of the systems, enhance the stabilization of the polaron and suppress the quantum increase of the classical polaron narrowing of electron band. Moreover, it add to the effects of nonadiabaticity on the minimum quantum uncertainty for the phonon coordinate by a strong coupling with the electron density for a large squeezing as compared with the adiabatic case and the uncorrelated case. Therefore, the new ansatz which can represent the correlation effects of displacement and squeezing is especially relevant for system with sufficiently large squeezing and strong coupling.