Stable He$^-$ can exist in a strong magnetic field

TL;DR

This study demonstrates that the helium negative ion (He$^-$) can form stable bound states in strong magnetic fields, with different spin configurations, for magnetic field strengths above approximately 0.13 atomic units.

Contribution

It provides the first evidence of stable He$^-$ ions in magnetic fields, identifying their energy states and spin configurations across a range of magnetic field strengths.

Findings

He$^-$ becomes bound for B > 0.13 a.u.

Two stable states of He$^-$ exist at certain magnetic fields.

The ground state transitions from spin-doublet to spin-quartet with increasing B.

Abstract

The existence of bound states of the system $(\al,e,e,e)$ in a magnetic field $B$ is studied using the variational method. It is shown that for $B \gtrsim 0.13\,{\rm a.u.}$ this system gets bound with total energy below the one of the $(\al,e,e)$ system. It manifests the existence of the stable He$^-$ atomic ion. Its ground state is a spin-doublet $^2(-1)^{+}$ at $0.74\, {\rm a.u.} \gtrsim B \gtrsim 0.13\, {\rm a.u.}$ and it becomes a spin-quartet $^4(-3)^{+}$ for larger magnetic fields. For $0.8\, {\rm a.u.} \gtrsim B \gtrsim 0.7\, {\rm a.u.}$ the He$^-$ ion has two (stable) bound states $^2(-1)^{+}$ and $^4(-3)^{+}$.