| We have recently reported the existence of superlight small bipolarons on lattices formed from triangular plaquettes [J.P.Hague, P.E.Kornilovitch, J.H.Samson and A.S.Alexandrov, Phys. Rev. Lett, 98, 037002 (2007)]. Such bipolarons can exist due to the combination of an inter-site electron-phonon interaction and strong local Hubbard repulsion, which leads to an inter-site pair (or dimer in the strong coupling limit). Dimers bound in this way are very mobile, because the triangular lattice allows the dimer to move with a single electron hop [J.P.Hague, P.E.Kornilovitch, J.H.Samson and A.S.Alexandrov, J. Phys.: Condens. Matter, 19 (2007) 255214], as we demonstrate with a simple analytic picture [J.P. Hague, P.E. Kornilovitch, J.H. Samson and A.S. Alexandrov. J. Phys.: Conf. Ser. 92, 012118 (2007)]. The pressing question remains the stability of bipolarons: Over which range of the parameter space are bipolarons bound? Do pairs of bipolarons survive clustering? In this presentation we use analytics and a continuous time quantum Monte Carlo algorithm to gain insight into this question. Using our bipolaron algorithm, we are able to compute binding energies, masses, the bipolaron spectrum and density of states. We extend our algorithm so that four (or more) polarons can be simulated, and discuss the binding vs clustering of bipolarons. We also discuss trapping of polarons by impurities |
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