Radio frequency field-induced electron mobility in an ultracold plasma state of arrested relaxation

TL;DR

This study investigates how a weak radiofrequency field can mobilize electrons in an ultracold nitric oxide plasma, revealing a suppressed electron mobility state that endures longer than expected due to quenched disorder and collective effects.

Contribution

It demonstrates that a low-amplitude RF field can significantly increase electron mobility in an ultracold plasma, highlighting a novel arrested relaxation state influenced by collective interactions.

Findings

RF field mobilizes electrons, causing plasma dissipation

Electron mobility depends on plasma density and collisions

Plasma exhibits characteristics of self-organized criticality

Abstract

Penning ionization releases electrons in a state-selected Rydberg gas of nitric oxide entrained in a supersonic molecular beam. Subsequent processes of electron impact avalanche, bifurcation, and quench form a strongly coupled, spatially correlated ultracold plasma of NO$^+$ ions and electrons that exhibits characteristics of self-organized criticality. This plasma contains a residue of nitric oxide Rydberg molecules. A conventional fluid dynamics of ion-electron-Rydberg quasi-equilibrium predicts rapid decay to neutral atoms. Instead, the NO plasma endures for a millisecond or more, suggesting that quenched disorder creates a state of suppressed electron mobility. Supporting this proposition, a 60 MHz radiofrequency field with a peak-to-peak amplitude less than 1 V cm$^{-1}$ acts dramatically to mobilize electrons, causing the plasma to dissipate by dissociative recombination and Rydberg predissociation. An evident density dependence shows that this effect relies on collisions, giving weight to the idea of arrested relaxation as a cooperative property of the ensemble.