Regensburg 2013 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 25: Correlated Electrons: Low-Dimensional Systems - Models 3
TT 25.1: Talk
Tuesday, March 12, 2013, 09:30–09:45, H9
Interacting Fröhlich and Holstein bipolarons — •Monodeep Chakraborty1, Masaki Tezuka2, and Byung Il Min1 — 1Department of Physics, POSTECH, Pohang, 790-784, Korea — 2Department of Physics, Kyoto University, Kyoto 606-8502, Japan
Polarons and bipolarons have been long-term subjects of interest in many areas of condensed matter. We have investigated the bipolaron-bipolaron interaction for the Holstein-Hubbard (HH) and the Fröhlich-Hubbard(FH) model on a discrete one-dimensional (1D) lattice. We have generated a variational space by repeated application of our chosen Hamiltonian on a initial state and then used conjugate-gradient technique to obtain the ground state energy as well as the wave-function for a few electron (two, four and six) and phonon system. The HH model has also been studied with density-matrix renormalization group (DMRG). Both methods lead to the same conclusion that there exists no bipolaron-bipolaron attraction in the HH model. However, we obtain clear cut bipolaron-bipolaron attraction within the Fröhlich paradigm above a critical electron-phonon coupling forming the bipolaron cluster. The bipolaron cluster can survive in spite of the Hubbard-U effect up to a finite U and then separates into individual bipolarons or polarons. The bipolaron-bipolaron attraction could be a possible mechanism of the phase separation in many condensed matter systems with the strong electron-phonon interaction.