Optical orientation of nuclei in nitrogen alloys GaAsN at room temperature

TL;DR

This study investigates nuclear polarization in GaAsN nitrogen alloys at room temperature, revealing a dynamic nuclear field influenced by optical pumping and hyperfine interactions, with implications for spintronics.

Contribution

It demonstrates the presence of a nuclear field in GaAsN alloys that saturates with excitation intensity, highlighting hyperfine interactions as the main polarization mechanism.

Findings

Internal nuclear field Beff reaches saturation (~250 Gauss) at high excitation densities.

Nuclear polarization occurs rapidly (<15 microseconds), indicating interaction with localized electrons.

The nuclear field is driven by hyperfine interaction, not exchange interaction.

Abstract

The intensity and the giant circular polarization of edge luminescence in a longitudinal magnetic field have been measured in nitrogen alloys GaAsN under circularly polarized pumping. It has been found that these dependences are shifted with respect to zero field by a value Beff. The magnitude of the internal field Beff increases with increase in pumping intensity and reaches saturation (~250 Gauss) at great densities of excitation. The saturation of the Beff field with growth of pumping indicates that this is a field of nuclei, polarized dynamically due to hyperfine interaction with optically oriented deep paramagnetic centers, rather than a field of exchange interaction created on the center by spin-polarized photo-excited conduction electrons. The short time of nuclear polarization by electrons (<15 mks), measured under modulation of circular polarization of the exciting light with high frequency, points to a small number of nuclei undergoing hyperfine interaction with an electron localized at a center.