Evolution of the excited electron bubble in liquid 4He and the appearance of fission-like processes

TL;DR

This study investigates how excited electron bubbles in superfluid helium-4 evolve over time, revealing pressure-dependent decay paths and the emergence of fission-like processes, aligning with experimental observations.

Contribution

It introduces a combined liquid-electron dynamical model showing pressure-dependent decay mechanisms and the appearance of fission-like processes in excited electron bubbles.

Findings

Below 1 bar, excited bubbles decay radiatively to the ground state.

Above 1 bar, bubble fission-like processes occur with electron localization in baby bubbles.

The 2P bubble evolution involves non-adiabatic state crossings.

Abstract

We have studied the evolution of an excited electron bubble in superfluid 4He for several tens of picoseconds combining the dynamics of the liquid with an adiabatic evolution for the electron. The path followed by the excited bubble in its decay to the ground state is shown to strongly depend on pressure. While for pressures below 1 bar the 1P excited electron bubble has allowance for radiatively decay to the deformed ground state, evolving then non-radiatively towards the ground state of the spherical electron bubble, we have found that above 1 bar two distinct baby bubbles appear in the course of the dynamical evolution, pointing to a different relaxation path in which the electron may be localized in one of the baby bubbles while the other collapses, allowing for a pure radiationless de-excitation. Our calculations are in agreement with experiments indicating that relaxed 1P bubbles are only observed for pressures smaller than a critical one, of the order of 1 bar, and that above this value the decay of the excited bubble has to proceed differently. A similar analysis carried out for the 2P bubble shows that the adiabatic approximation fails at an early stage of its dynamical evolution due to the crossing of the 2P and 1F states.