Multi-carrier states in the Peierls electron-phonon model

Motivated by the discovery of light polarons and bipolarons in the Peierls electron-phonon model on a one dimensional lattice [1], we numerically study few-carrier states (up to six) using the density matrix renormalization group method. Our results show that a bipolaron liquid is a stable ground state in a wide range of phonon frequencies and electron-phonon interaction strengths. More interestingly, we provide numerical evidence that this homogeneous multi-carrier state for a sufficiently large electron-phonon coupling strength becomes unstable in favor of a multi-polaron complex suggestive of phase separation. We provide analytical arguments in support of our numerics based on an effective multi-body interaction
between electrons mediated by phonons [2]. We finally show preliminary results for the case of two coupled chains and discuss the implications of the results for two dimensional systems.

[1] J. Sous, M. Chakraborty, R. V. Krems, and M. Berciu, Phys. Rev. Lett. 121 247001 (2018)
[2] A. Nocera, J. Sous, and M. Berciu, (in preparation)