Model of Nonadiabatic to Adiabatic Dynamical Quantum Phase Transition in Photoexcited Systems

TL;DR

This paper presents a model describing how nonadiabatic to adiabatic transitions in photoexcited systems lead to metastable states and significantly affect recovery times, explaining experimental phenomena in manganites.

Contribution

It introduces a new theoretical framework linking quantum phase transitions to ultrafast dynamics in photoexcited materials, with applications to manganites.

Findings

Abrupt tunneling blockade creates metastable states.

Quantum critical transition causes large recovery time differences.

Explains structural bottlenecks and rearrangements in experiments.

Abstract

We study the ultrafast dynamic process in photoexcited systems and find that the Franck-Condon or Landau-Zener tunneling between the photoexcited state and the ground state is abruptly blocked with increasing the state coupling from nonadiabatic to adiabatic limits. The blockage of the tunneling inhibits the photoexcited state from decaying into the thermalized state and results in an emergence of a metastable state, which represents an entanglement of electronic states with different electron-phonon coupling strengths. Applying this model to the investigation of photoexcited half-doped manganites, we show that the quantum critical transition is responsible for more than three orders of magnitude difference in the ground state recovery times following photoirradiation. This model also explains some elusive experimental results such as photoinduced rearrangement of orbital order by structural rather than electronic process and the structural bottleneck of one-quarter period of the Jahn-Teller mode. We demonstrate that in the spin-boson model there exist unexplored regions not covered in the conventional phase diagram.