Electron spin dynamics of Ce$^{3+}$ ions in YAG crystals studied by pulse-EPR and pump-probe Faraday rotation

TL;DR

This study investigates the spin relaxation and coherence properties of Ce$^{3+}$ ions in YAG crystals using pulse-EPR and pump-probe Faraday rotation, revealing relaxation times, phonon interactions, and hyperfine effects.

Contribution

It provides detailed measurements of spin dynamics and relaxation mechanisms of Ce$^{3+}$ ions in YAG, combining two advanced spectroscopic techniques for the first time.

Findings

Millisecond spin-lattice relaxation time $T_1$ at low temperatures

Microsecond spin coherence time $T_2$

Hyperfine interactions with $^{27}$Al nuclei observed

Abstract

The spin relaxation dynamics of Ce$^{3+}$ ions in heavily cerium-doped YAG crystals is studied using pulse-electron paramagnetic resonance and time-resolved pump-probe Faraday rotation. Both techniques address the 4$f$ ground state, while pump-probe Faraday rotation provides also access to the excited 5$d$ state. We measure a millisecond spin-lattice relaxation time $T_1$, a microsecond spin coherence time $T_2$ and a $\sim 10$ ns inhomogeneous spin dephasing time $T_2^*$ for the Ce$^{3+}$ ground state at low temperatures. The spin-lattice relaxation of Ce$^{3+}$ ions is due to modified Raman processes involving the optical phonon mode at 125 cm$^{-1}$. The relaxation at higher temperature goes through a first excited level of the $^{2}$F$_{5/2}$ term at about $\hbar \omega \approx 228$ cm$^{-1}$. Effects provided by the hyperfine interaction of the Ce$^{3+}$ with the $^{27}$Al nuclei are observed.