Speaker
Description
We develop and compare analytical approaches for the polaron problem in finite-width, non-parabolic conduction bands [1, 2]. Our main result is an extension of the Feynman variational method to tight-binding lattices [1], where the effective-mass approximation breaks down. We also revisit analytical methods originally formulated for continuum polarons, including canonical transformations and improved self-consistent Wigner–Brillouin approximations, and generalize them to lattice systems. In a finite-bandwidth lattice, these approaches exhibit qualitative features absent in the continuum case, such as a nontrivial connection between weak- and strong-coupling limits. An improved Wigner–Brillouin scheme yields a momentum-dependent polaron self-energy free of resonances and consistent with perturbation theory at zero momentum.
The methods are applied to the Holstein model and benchmarked against numerically exact calculations, including Diagrammatic Monte Carlo, exact diagonalization, and density-matrix renormalization-group results, and are further extended to polarons with Rashba spin–orbit coupling.
The self-energy of a Holstein polaron exhibits close agreement between the modified Feynman variational method and numerically exact results. The developed approaches are promising for theoretical study of polarons with different types of the particle-phonon interaction.
References
[1] S. N. Klimin, J. Tempere, M. Houtput, I. Zappacosta, S. Ragni, T. Hahn, L. Celiberti, C. Franchini and A. S. Mishchenko, arXiv:2603.09609 (2026)
[2] S. N. Klimin, J. Tempere, M. Houtput, S. Ragni, T. Hahn, C. Franchini and A. S. Mishchenko, Phys. Rev. B 110, 075107 (2024).