Ensemble spin relaxation of shallow donor qubits in ZnO
Vasileios Niaouris, M. V. Durnev, Xiayu Linpeng, Maria Viitaniemi, Christian Zimmermann, Aswin Vishnuradhan, Yusuke Kozuka, M. Kawasaki, Kai‐Mei C. Fu
Abstract
We present an experimental and theoretical study of the longitudinal electron spin relaxation (${T}_{1}$) of shallow donors in the direct band-gap semiconductor ZnO. ${T}_{1}$ is measured via resonant excitation of the Ga donor-bound exciton. ${T}_{1}$ exhibits an inverse-power dependence on magnetic field ${T}_{1}\ensuremath{\propto}{B}^{\ensuremath{-}n}$, with $4\ensuremath{\le}n\ensuremath{\le}5$, over a field range of 1.75 T to 7 T. We derive an analytic expression for the donor spin-relaxation rate due to spin-orbit (admixture mechanism) and electron-phonon (piezoelectric) coupling for the wurtzite crystal symmetry. Excellent quantitative agreement is found between experiment and theory suggesting the admixture spin-orbit mechanism is the dominant contribution to ${T}_{1}$ in the measured magnetic field range. Temperature and excitation-energy dependent measurements indicate a donor density dependent interaction may contribute to small deviations between experiment and theory. The longest ${T}_{1}$ measured is 480 ms at 1.75 T with increasing ${T}_{1}$ at smaller fields theoretically expected. This work highlights the extremely long longitudinal spin-relaxation time for ZnO donors due to their small spin-orbit coupling.