SPIN TRANSPORT OF EXCITON MAGNETIC POLARONS IN DILUTED MAGNETIC SEMICONDUCTOR
MULTIPLE QUANTUM WELLS. Gregory A. Balchin* and Leigh M. Smith, University
of Cincinnati, Cincinnati, OH and Berry T. Jonker, Naval Research Lab, Washington,
D.C. (NIST address: Building 225, Room A305, Gaithersburg, MD 20899, 301-975-6582,
Spatially- and temporally-resolved photoluminescence was used to measure,
for the first time, the spin transport of long-lived Type-II exciton magnetic
polarons in Zn1-xMnxSe/ZnSe multiple quantum wells.
The experimental setup involved the design and construction of a passively
mode-locked Ti:Sapphire laser as well as a 20 /0.5 NA microscope objective
inside a variable-temperature cryostat. We find that the free
excitons diffuse very little during their 150 ps lifetime. In contrast,
the effective diffusivity (D = 25 cm2/s)
of the exciton magnetic polaron is 2- to 3- orders of magnitude larger than
for the bare excitons. This is unexpected since the exciton magnetic polaron
involves a free exciton dressed by the local polarization of the Mn-impurities,
and therefore the diffusion should be less than that for the free excitons.
The value of the diffusivity corresponds to an unphysically large mobility
(105 cm2/Vs) which may be evidence for
a strong repulsive force between the exciton magnetic polarons.
*Semiconductor Electronics Division, NIST, Gaithersburg, MD