Detection and decoherence of level-crossing resonances of ${}^8$Li in Cu

Level-crossing resonances are observed for spin-polarized ${}^8$Li in copper at 200 K. The positions of the resonances as a function of magnetic field and crystal orientation are a precise measure of the induced quadrupolar interaction on the nearest-neighbor Cu spins and provide unambiguous evidence that ${}^8$Li occupies a substitutional site. The resonances are detected as enhancements in the ${}^8$Li spin relaxation rate and are much broader than predicted from a static spin Hamiltonian. A strong collision model is used to extract a decoherence time as a result of the dipolar coupling of the ${}^8$Li-Cu subsystem to the surrounding nuclear spin bath.

Figure 1

Representative examples of the normalized ${}^8$Li asymmetry at 200 K in Cu with B parallel to a $\langle 110\rangle$ crystalline direction. The solid lines are fits to the data. The inset illustrates the time evolution of the ${}^8$Li polarization in the strong collision model of the relaxation rate.

Figure 2

Top three panels are the experimental $1/T_1$ for B applied parallel to the $\langle 100\rangle$, $\langle 110\rangle$, and $\langle 111\rangle$ orientations of Cu. The lower three panels are simulations as described in the text. Also shown is the fcc lattice of Cu with the ${}^8$Li in a substitutional site.