ESR<i>in Situ</i>with a Josephson Tunnel Junction

Abstract

The in situ electron-spin resonance of a voltage-biased NbAuNb Josephson junction is reported. The Au barrier is doped with Gd or $^{167}\mathrm{Er}$ ions. Sharp resonances appear in the $I\ensuremath{-}V$ curves at frequencies equivalent to the crystal-field splitting of $\mathrm{Au}\mathrm{Gd}$ (1.0 and 1.7 GHz) and to the hyperfine splitting of $\mathrm{Au}^{167}\mathrm{Er}$ (2.87 GHz). The principle of this new type of ESR-Josephson-junction spectrometer, as well as its application, is discussed.