Experimental measurement of the isolated magnetic susceptibility

TL;DR

This paper presents a clear experimental method to measure the isolated magnetic susceptibility in a dilute spin ice system, revealing its relation to quantum state superpositions and populations at nuclear-electronic level crossings.

Contribution

It provides the first unambiguous measurement of the isolated susceptibility, linking it to quantum superpositions and state populations in a real material.

Findings

Measured $oldsymbol{oldsymbol{ ext{isolated susceptibility}}}$ at avoided crossings.

Linked susceptibility to quantum superposition and state populations.

Demonstrated the measurement in a dilute spin ice with holmium ions.

Abstract

The isolated susceptibility $\chi_{\rm I}$ may be defined as a (non-thermodynamic) average over the canonical ensemble, but while it has often been discussed in the literature, it has not been clearly measured. Here, we demonstrate an unambiguous measurement of $\chi_{\rm I}$ at avoided nuclear-electronic level crossings in a dilute spin ice system, containing well-separated holmium ions. We show that $\chi_{\rm I}$ quantifies the superposition of quasi-classical spin states at these points, and is a direct measure of state concurrence and populations.