Gigantic spin-noise gain enables magnetic resonance spectroscopy of impurity crystals

TL;DR

This paper demonstrates that spin noise spectroscopy can be effectively used to detect magnetic resonance in impurity crystals by leveraging a giant spin-noise gain effect, especially for rare-earth ions with narrow homogeneous linewidths.

Contribution

It introduces the concept of spin-noise gain in impurity crystals and applies it to detect magnetic resonance of rare-earth ions for the first time.

Findings

Spin-noise gain can reach 10^8 for certain impurity transitions.

Spin noise spectroscopy successfully detects magnetic resonance in rare-earth doped crystals.

Homogeneous linewidth reduction enhances spin-noise signals significantly.

Abstract

Spin noise spectroscopy is a method of magnetic resonance widely used, nowadays, in atomic and semiconductor research. Classical objects of the EPR spectroscopy - dielectrics with paramagnetic impurities - seemed to be unsuitable for this technique because of large widths of allowed optical transitions and, therefore, low specific Faraday rotation (FR). We show, however, that the FR noise detected at the wavelength of a weak optical transition (with low regular FR) may increase by many orders of magnitude as its homogeneous width decreases. This spin-noise gain effect, numerically described by the ratio of the inhomogeneous linewidth to homogeneous, relates primarily to forbidden intraconfigurational transitions of impurity ions with unfilled inner electronic shells. Specifically, for the f-f transitions of rare-earth ions in crystals, this factor may reach 10$^8$. In this paper, we report on the first successful application of spin noise spectroscopy for detecting magnetic resonance of rare-earth ions in crystals.