Magnetic Polaron Formation in Semimagnetic Semiconductor Heterostructures

Abstract

We present a survey of experimental and theoretical studies of exciton magnetic polarons in semimagnetic semiconductor epilayers, quantum wells and superlattices. The emphasis is on dynamical aspects of magnetic polaron formation in systems of different dimensionality.

Ultra-Fast Spin Dynamics in Diluted Magnetic Semiconductors

“…Thus, it is clear, without any detailed analysis, that for a random set of AF clusters a considerable effect of the binding of EMP occurs when the characteristic length of the clusters is larger than the exciton Bohr radius. Such behaviour is well confirmed by the experimental data [2,3] -a non-zero binding of EMP appears for alloy compositions x > 0.1, i.e., for alloys where the mean size of the AF cluster becomes comparable to the Bohr radius. For smaller composition no EMP effect is observed; clusters are smaller than the exciton size.…”

“…In particular, the characteristic time for the creation of an exciton magnetic polaron (EMP) is extremely short. It is much faster than any longitudinal relaxation time [1][2][3]. In addition, there is a "mysterious" coupling between antiferromagnetic (AF) layers in antiferromagnet-semiconductor superlattices [4] and also between antiferromagnetic micrograins which are characterised by a new type of magnetic resonance [5].…”

“…The energy gain caused by this mechanism is, usually, smaller as compared to the energy gain caused by the Curie-Weiss magnetization. It becomes of similar magnitude for very small AF where at least one dimension is reduced to a few inter-atomic distances, like in nanoAF grains [3], or AF/semiconductor superlattices [2,4] or diluted magnetic semiconductors [4] which can be treated as a set of random mesoscopic AF clusters.…”

Influence of exciton spin relaxation on the photoluminescence spectra of semimagnetic quantum dots

“…For samples with x ≥ 0.05 we do not expect any significant variations of the Mn spin temperature with the magnetic field, since for such large Mn densities the heat transferred from the hot photocarriers is efficiently dissipated via the spin-lattice relaxation, which is enhanced in the presence of stronger spinspin interactions. 30,31 However, for the samples in which the complete EMP formation occurs during the exciton lifetime (x = 0.1 and x = 0.2), the transition redshift significantly affects the time-integrated PL linewidth (see data points below 1 T in Fig. 6(f)), and hence data points below 1 T are omitted.…”

“…27 Thus, in order to achieve the equilibrium, the Mn magnetization dynamics has to occur on a timescale of 1-100 ps, much shorter than those driven by spin-lattice interactions, which occur on the µs/ms timescales. 30,31 The spin-spin mechanism becomes efficient only if the average distance between Mn spins is small enough. Consequently, EMP formation was unambiguously demonstrated only for dots with a Mn content x ≥ 0.1.…”