Детектирование переноса спинового возбуждения в двумерной электронной системе по фотолюминесценции многочастичных экситонных комплексов

Письма в Журнал экспериментальной и теоретической физики. 2017. Т. 106. № 10. С. 651–654.

Горбунов А. В., Кулик Л. В., Kuznetsov V., Журавлёв А. С., Ларионов А. В., Тимофеев В. Б., Kukushkin I.

We demonstrate that non-equilibrium spin excitations drift to macroscopically large distances in a 2D electron gas (symmetrically doped GaAs/AlGaAs quantum well) in a quantizing magnetic field at filling factor $\nu $ = 2. The effect is induced by low-temperature photoexcitation of a dense ensemble of long-lived ($\sim 1 $ ms) spin excitations − cyclotron spin-flip magnetoexcitons. The spin excitation is a bound state of an electron at the first Landau level and a Fermi-hole at the zeroth
Landau level with a total spin S = 1 [1-3]. Direct photoexcitation and radiative annihilation of such excitations are forbidden (“dark” excitons), yet, their binding energy and spin structure are reliably established by inelastic light scattering spectra [4, 5]. Recently, we were able to measure the dark exciton density and relaxation rate by newly developed technique – photo-induced resonant light reflection [6]. At the temperatures below 1 K, we discovered the condensate-like
behavior of the dense exciton ensemble [7]. Furthermore, these spin excitations modify photoluminescence spectrum by binding to a photo-excited valence hole: an allowed radiative recombination channel of three-particle complexes gets active [8]. Our paper presents observation of spin exciton drift to the distance up to 200 μm. This unique phenomenon was experimentally studied utilizing spatial separation of pump (photoexcitation) and probe (photoluminescence detection) laser spots. Enhancement of the multi-particle complexes in photoluminescence spectrum was observed far away from the pump area. Both pump intensity
and temperature dependencies correlate well with the phase diagram of dark exciton condensation [7]. Time dependence of the spin drift rate in a 2D electron gas is the subject of our near-future research.

Keywords: semiconductors, полупроводники, целочисленный квантовый эффект Холла, неравновесные эффекты, quantum Hall effect, Photoluminescence, Фотолюминесценция, nonequilibrium phenomena