Cryogenic Microwave Whispering Gallery Mode Spectroscopy of Paramagnetic Impurities in High-Purity Crystalline LiF

Abstract

A low-noise cryogenic microwave spectroscopy experiment was performed on a high-purity lithium fluoride (LiF) crystal. The spectroscopy data revealed avoided level crossing interactions in whispering gallery modes, indicative of electron spin resonance (ESR) coupling with paramagnetic impurities. Analysis of the interaction spectra identified distinct spin systems corresponding to $(S=3/2,I=7/2)$, $(S=1,I=7/2)$, and $(S=3/2,I=0)$. The number of hyperfine splittings observed, together with the natural abundance of ions possessing the appropriate nuclear spin values, suggest that V${}^{2+}$ and V${}^{3+}$ impurities, exhibiting orthorhombic distortion, are the most likely sources of the narrow interaction features. This interpretation is supported by earlier ESR studies and established manufacturing records for LiF crystal growth. Additionally, a separate set of broader interaction points is consistent with an orthorhombic model involving a $(S=3/2,I=0)$ spin system, although the specific impurity responsible for this interaction remains unidentified.

References in corpus (8)

• Cavity QED with magnetically coupled collective spin states
• Anisotropic rare-earth spin ensemble strongly coupled to a superconducting resonator
• Rare earth spin ensemble magnetically coupled to a superconducting resonator
• High Q-factor Sapphire Whispering Gallery Mode Microwave Resonator at Single Photon Energies and milli-Kelvin Temperatures
• Low-Temperature Microwave Properties of Biaxial YAlO3
• Precision Multi-Mode Microwave Spectroscopy of Paramagnetic and Rare-Earth Ion Spin Defects in Single Crystal Calcium Tungstate
• Low temperature properties of whispering gallery modes in isotopically pure silicon 28
• On the degeneracy of whispering gallery modes in a high-Q sapphire microwave resonator