Motional Enhancement of the Exciton Magnetic Momentum
A.Litvinov, V.Kochereshko
A.F.Ioffe Physico-Technical Institute RAS, 194021 St. Petersburg, Russia
R.Cox, H.Mariette, H.Boukari
Laboratoire de Spectrométrie Physique, Universit´e Joseph Fourier de Grenoble, France
Yu.Efimov S.Eliseev, Yu.Dolgikh
Institute of Physics, St. Petersburg State University, St. Petersburg, Russia.
J.J.Davies
Department of Physics, University of Bath, Bath BA2 7AY, UK
In magneto-optics of excitons the exciton center of mass motion is usually neglected. This is
caused, first of all, by the fact that, generally, only excitons with very small wave-vector
K

c
n  10 5 cm 1 and small kinetic energy (or even localized exciton states) participate in
optical experiments. Spectroscopy of moving excitons is difficult because such excitons cannot
interact with photons.
It is usually accepted, that exciton magnetic momentum in stationary state is defined by the
sum of electron and hole magnetic moments. The exciton center of mass motion can
significantly change, or even bring new magnetic properties, of the exciton. The first
experimental observations of such phenomena were reported in [1, 2]. Recently authors have
observed a new effect of “Motional Enhancement of the Exciton Magnetic Momentum” (MEM)
[3]. This means that the exciton magnetic momentum (exciton g-factor) increases for the
moving exciton proportionally to it kinetic energy.
The states of exciton quantization correspond to different energies in quantum well
structure and the higher number of state the higher is the exciton kinetic energy. This property
allows us to study exiton states in motion i.e. states with non-zero kinetic energy.
In the present paper we have studied magneto-reflectivity spectra in Faraday geometry
H K [100] in magnetic fields up to 8Т taken from structures with wide quantum well (the
well width is much bigger the exciton Bohr radius) based on GaAs, CdTe and ZnTe. In such
structures exciton center of mass quantization occurs [4]. A distinctive feature of these
structures is that different kinds of mechanical strains, caused by barrier and well lattice
constants mismatch, are fulfilled. GaAs/AlGaAs-based structures are not strained and the states
of light and heavy hole excitons are degenerate. CdTe/CdZnTe-based structures are strained,
thus the heavy hole exciton forms the ground state while the light hole exciton state lays
20meV towards higher energies. In ZnTe/ZnMgTe-based structures the light exciton is, vice
versa, energetically lower by 15meV than the heavy hole exciton.
We have observed enhancement of the exciton magnetic momentum (more than 10 times)
proportionally to the number of quantization level in all these structures. This has been
particularly manifested for the light and heavy hole excitons. Such phenomenon is explained
by the influence of cubic in k-term in valence band, which mix 1S and nP exciton states. A
theoretical model that is in good agreement with experimental data has been developed. Also,
we have observed decrease of the exciton diamagnetic shift with the increase of its kinetic
energy in magnetic fields.
References:
[1] D. G. Thomas and J. J. Hopfield Phys. Rev. 124, 657-665 (1961)
[2] E.F.Gross, B.P.Zakharchenia, O.V.Konstantinov
Soviet Physics. Solid State 3, 305,
(1961)
[3] J.J.Davies, D.Wolverson, V.P.Kochereshko, et al. Phys. Rev. Lett. 97, 187403 (2006)
[4] V.A.Kiselev, B.S.Razbirin, I.N.Uraltsev
Phys. Status Solidi B72, 161, (1975) and
H.Tuffigo, R.T.Cox, N.Magnea, Y.Merle d’Aubigne A.Million Phys. Rev. B37, 4310, (1988)