Time dependence of the Hanle effect in the emission of triplet bound excitons in gallium selenide
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Time Dependence of the Hanle Effect in the Emission of Triplet Bound Excitons in Gallium Selenide A. N. Starukhin, D. K. Nelson, and B. S. Razbirin Ioffe Physicotechnical Institute, Russian Academy of Sciences, Politekhnicheskaya ul. 26, St. Petersburg, 194021 Russia email: [email protected] Received January 15, 2010
Abstract—The dynamics of the magneticfieldinduced depolarization of the circularly polarized radiation of spinoriented triplet bound excitons in uniaxial crystals has been studied by timeresolved spectroscopy on an example of GaSe. The depolarization of radiation (the Hanle effect) is due to the difference between the behaviors of its σ+ and σ– components in a magnetic field. It has been found that the magneticfield depen dences of the σ+ and σ– component intensities vary considerably within the lifetime t of the excited states. The form of the magneticfield dependence of the degree of polarization of the exciton radiation remains generally the same for various t values. A theoretical description of these effects has been proposed. DOI: 10.1134/S1063776110100158
1. INTRODUCTION The effects caused by magneticfieldinduced change in the optical properties of the medium are widely used to solve fundamental and applied prob lems. The Hanle effect [1] is one of the widely known magnetooptical effects. The effect is a decrease in the degree of polarization of light emitted by objects intro duced into an external magnetic field due to the mag neticfield dependence of radiation intensity (in a given direction and with a certain polarization). This phenomenon is commonly treated as a result of the crossing and interference of the Zeeman sublevels of the excited state of the system in zero magnetic field. The Hanle effect is of interest due to its high efficiency in the investigation of the energy structure and kinetics of excited states in various atomic systems from atoms to crystals [2–7]. The investigations of the Hanle effect in semicon ductors were additionally stimulated after the discov ery of the phenomena of the optical orientation of electrons and excitons [3]. A system of oriented exci tons emits circularly polarized light whose state (σ+ or σ–) in the case of optical orientation is determined by the polarization state of pump light. The application of the external magnetic field B perpendicular to the light propagation direction is accompanied by a decrease in the degree of circular polarization of the exciton radi ation (Hanle effect) given by the expression I σ– ( B ) – I σ+ ( B ) P circ ( B ) = . I σ– ( B ) + I σ+ ( B )
(1)
Here, I σ+− (B) are the intensities of the radiation com ponents with left and right circular polarizations, respectively.
The depolarization of the radiation of oriented excitons by the external magnetic field is due to the difference between the behaviors of radiation compo nent intensities I σ+− (B) in the magnetic field. In the case of cw pumping, the magneticfield dependences − of the i
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