Survival of the SSH polaron sharp effective-mass transition in the adiabatic limit

Establish whether the sharp transition in the effective mass of the Su–Schrieffer–Heeger (SSH) polaron persists in the adiabatic regime characterized by low phonon frequencies (Ω/4t ≪ 1).

Background

The SSH model describes electron–phonon coupling that modulates hopping amplitudes and is known to produce a sharp transition in polaron properties (e.g., effective mass and ground-state momentum) at high phonon frequencies (the anti-adiabatic regime). In contrast, the Holstein model, which couples phonons to on-site energies, does not exhibit this behavior.

Accurate numerical treatment at low phonon frequencies (the adiabatic regime) is challenging due to the rapid growth of the phonon Hilbert space. As a result, it remains unresolved whether the sharp transition established in the anti-adiabatic regime survives in the adiabatic limit. The present paper develops ML-based extrapolations to probe this question but acknowledges the underlying uncertainty.

References

It is not understood if the sharp transition observed in the effective mass for the SSH polaron survives and whether the SSH bipolarons with low effective mass may form at strong coupling in the adiabatic regime.

— Extrapolation of polaron properties to low phonon frequencies by Bayesian machine learning  (2312.09991 - Kairon et al., 2023) in Introduction, paragraph preceding the sentence beginning “Motivated by this uncertainty…”