Magnon condensation into Q-ball in 3He-B

TL;DR

This paper reports the experimental realization of magnon condensation into Q-balls in superfluid 3He-B, demonstrating long-lived magnetic signals and self-localization effects analogous to relativistic quantum field theories.

Contribution

It provides the first experimental observation of Q-balls in a condensed matter system, linking relativistic field theory concepts with superfluid helium-3 behavior.

Findings

Observation of long-lived Persistent Signal in NMR

Detection of self-localization of magnons

Evidence of phase coherent spin precession

Abstract

The theoretical prediction of Q-balls in relativistic quantum fields is realized here experimentally in superfluid 3He-B. The condensed-matter analogs of relativistic Q-balls are responsible for an extremely long lived signal of magnetic induction -- the so-called Persistent Signal -- observed in NMR at the lowest temperatures. This Q-ball is another representative of a state with phase coherent precession of nuclear spins in 3He-B, similar to the well known Homogeneously Precessing Domain which we interpret as Bose condensation of spin waves -- magnons. At large Q the effect of self-localization is observed. In the language of relativistic quantum fields it is caused by interaction between the charged and neutral fields, where the neutral field provides the potential for the charged one. In the process of self-localization the charged field modifies locally the neutral field so that the potential well is formed in which the charge is condensed.