Spin relaxation in inhomogeneous quantum dot arrays studied by electron spin resonance

A. F. Zinovieva, N. P. Stepina, A. I. Nikiforov, A. V. Nenashev, A. V. Dvurechenskii, L. V. Kulik, M. C. Carmo, and N. A. Sobolev

Phys. Rev. B 89, 045305 – Published 16 January 2014

Abstract

Electron states in an inhomogeneous Ge/Si quantum dot array with groups of closely spaced quantum dots were studied by the conventional continuous-wave electron spin resonance and spin-echo techniques. We have found that the existence of quantum dot groups allows increasing the spin relaxation time in the system. The created structures permit us to change the effective localization radius of electrons by an external magnetic field. With the localization radius being close to the size of a quantum dot group, we obtain a fourfold increase in the spin relaxation time $T_{1}$ as compared to conventional homogeneous quantum dot arrays. This effect is attributed to an averaging of the local magnetic fields produced by $^{29}$ Si nuclear spins and a stabilization of the $S_{z}$ polarization during the electron back-and-forth motion within a quantum dot group.