Mobile inter-site bipolarons in presence of long-range interactions

J. Bonča, S. A. Trugman

J. P. Hague, P. E. Kornilovitch

We present details of a continuous-time quantum Monte Carlo algorithm for the screened Hubbard-Fr\"ohlich bipolaron. We simulate the bipolaron in one dimension with arbitrary interaction range in the presence of Coulomb repulsion, computing the effective mass, binding energy, total number of phonons associated with the bipolaron, mass isotope exponent, and bipolaron radius in a comprehensive survey of the parameter space. We discuss the role of the range of the electron-phonon interaction, demonstrating the evolution from Holstein to Fr\"ohlich bipolarons and we compare the properties of bipolarons with singlet and triplet pairing. Finally, we present simulations of the bipolaron dispersion. The bandwidth of the Fr\"ohlich bipolaron is found to be broad and the decrease in bandwidth as the two polarons bind into a bipolaron is found to be far less rapid than in the case of the Holstein interaction. The properties of bipolarons formed from long-range electron-phonon interactions, such as light strongly bound bipolarons and intersite pairing when Coulomb repulsion is large, are found to be robust against screening, with qualitative differences between Holstein and screened Fr\"ohlich bipolarons found even for interactions screened within a single lattice site.

J. T. Devreese, F. Brosens

N. S. Mondal, Subhadip Nath, S. Bose +1 more

An exact diagonalization calculation of the Hubbard model with inter-site electron-phonon interaction on a 2D square cluster shows that inter-site electron-phonon interaction effectively creates on-site (S0) bipolaron. There is also formation of neighboring site (S1) bipolaron. Entropy calculation shows that system goes into more ordered state with the formation of these self-trapped bipolaron.

Subhadip Nath, N. S. Mondal, K. Roy +1 more

We present a numerical study on the interplay between on-site electron-phonon (EP) interaction and inter-site Coulomb repulsion in the U/t =0.0 limit on a small cluster. Results show the formation of only S0 bipolarons. However, two polarons or bipolarons can be present at distances |i-j|=2. It is observed that inter-site Coulomb repulsion may favor formation of S0 bipolarons.

Vladimir M. Fomin, J. T. Devreese