V.V. Samartsev*, T.G. Mitrofanova**
Zavoisky Physical-Technical Institute, Kazan Scientific Center, Russian Academy of Sciences, Kazan, 420029 Russia
E-mail: *samartsev@kfti.knc.ru, **tagemi@mail.ru
Received November 23, 2017
Abstract
The possibility and the conditions of the formation of correlated “gratings” of electrons and their spins in a semiconductor film containing CdSe/CdS nanoparticles (which are the quantum dots) have been studied. Notably, the induction of electron spin “gratings” on quantum dots has been considered for the first time. We have suggested to perform an excitation of the film in the two photon absorption mode using two crossed (at an angle of 60?) femtosecond laser beams. As a result of the excitation, two nonequilibrium “gratings” are induced simultaneously in the excitation area of the film. If the exciting pulses have the same polarizations, then induced “gratings” of electrons are formed. However, in the case when the exciting pulses have mutually orthogonal polarizations, the formation of induced “gratings” of electron spins takes place. The same exciting pulses excite the electrons of CdSe/CdS nanoparticles into a superposition state. Then the free induction decay signal is generated. This signal being diffracted by induced “gratings” plays the role of a probe pulse in the suggested experimental scheme. The diffracted signals propagating in two mutually opposite directions are correlated (i.e., they are identical). Their wavefronts can carry the correlated transient holograms. Other possible applications of correlated “gratings” (in spintronics and in coherent femtosecond laser spectroscopy) are also discussed.
Keywords: correlated signals, quantum dots, induced electron and spin “gratings”, polarization, coincidence scheme, nonreversible relaxation time, coherent spectroscopy, spintronics
Acknowledgments. The study was supported by the Program of the Presidium of Russian Academy of Sciences ``Current Problems of Low Temperature Physics'' and by the Russian Foundation for Basic Research (project no. 17-02-00701a).
Figure Captions
Fig. 1. A device made of diffraction optics (DO) and confocal lens system for recording the induced ``gratings''.
Fig. 2. The induced ``gratings'' of non-equilibrium electrons ( a) and their spins ( b): a – electric field distribution in the area of overlapping between laser impulses with parallel polarization; b – electric field distribution in the area of overlapping between laser impulses with mutually perpendicular polarizations.
Fig. 3. The diffraction of the correlated coherent signals FID1 and FID2 on the simultaneously induced (with the femtosecond impulses k1 and k2) EPR ``gratings''. Designations: D1 and D2 – photodetectors, CdSe/CdS – sample, S – coincidence circuit. The parallel (1) and perpendicular (2) variants of polarization of excitation impulses. Variant (2) corresponds to the record of spin ``gratings''.
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For citation: Samartsev V.V., Mitrofanova T.G. Correlated induced electron and spin “gratings” in nanostructured CdSe/CdS. Uchenye Zapiski Kazanskogo Universiteta. Seriya Fiziko-Matematicheskie Nauki, 2018, vol. 160, no. 1, pp. 116–125. (In Russian)
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