# Arrested relaxation in an isolated molecular ultracold plasma

## TL;DR

This paper investigates how an isolated ultracold plasma formed from Rydberg nitric oxide exhibits arrested relaxation, leading to a stable, non-thermal state characterized by self-assembly, energy sequestration, and glass-like ion-electron separation.

## Contribution

It reveals a novel mechanism of energy-driven self-assembly and arrested relaxation in ultracold plasmas, demonstrating a stable, non-equilibrium state far from thermal equilibrium.

## Key findings

- Observation of plasma volume separation driven by kinetic energy
- Experimental evidence of complete ionization via electron spectroscopy
- Long-lived, stable non-thermal plasma state

## Abstract

Spontaneous avalanche to plasma splits the core of an ellipsoidal Rydberg gas of nitric oxide. Ambipolar expansion first quenches the electron temperature of this core plasma. Then, long-range, resonant charge transfer from ballistic ions to frozen Rydberg molecules in the wings of the ellipsoid quenches the centre-of-mass ion/Rydberg molecule velocity distribution. This sequence of steps gives rise to a remarkable mechanics of self-assembly, in which the kinetic energy of initially formed hot electrons and ions drives an observed separation of plasma volumes. These dynamics adiabatically sequester energy in a reservoir of mass transport, starting a process that anneals separating volumes to form an apparent glass of strongly coupled ions and electrons. Short-time electron spectroscopy provides experimental evidence for complete ionization. The long lifetime of this system, particularly its stability with respect to recombination and neutral dissociation, suggests that this transformation affords a robust state of arrested relaxation, far from thermal equilibrium.