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Photoluminescence Detected Doublet Structure
in the Integer and Fractional Quantum Hall Regime
F. M. Munteanu*,t, Yongmin Kim*, C. H. Perry*,t, D. G. Rickel*,
J. A. Simmonst, and J. L. Renot
'National High Magnetic Field Laboratory-Los Alamos National Laboratory
Los Alamos, NM 87545
tDepartment of Physics, Northeastern University, Boston, MA 02115
tSandia National Laboratory, Albuquerque, NM 87185
(May 6, 1999)
We present here the results of polarized magneto-photoluminescence measurements on a high mo-
bility single-heterojunction. The presence of a doublet structure over a large magnetic field range
(2>v>1/6) is interpreted'as possible evidence for the existence of a magneto-roton minima of the
charged density waves. This is understood as an indication of strong electronic correlation even in
the case of the IQHE limit.The use of magneto-photoluminescence (MPL) spec-
troscopy to study the integer (IQHE) and fractional
quantum Hall effects (FQHE) has attracted considerable
interest in recent years. In the case of the IQHE, the ap-
pearance of the gap in the spectrum at the Fermi energy
is caused by the quantization of the magnetic Landau
levels or the quantization of the spin energy levels and is
essentially a single particle phenomenon. In the case of
FQHE, the appearance of the gap is understood as a re-
sult of condensation of the 2 DEG into an incompressible
quantum liquid (IQL)1 due to strong electron-electron
correlations which takes place at fractional filling factors
z=p/q<1.
One of the most significant phenomenon that occurs in
the FQHE regime is the emergence of low-lying charge-
density (CD) waves that display characteristic magneto-
roton (MR) minima at a wave vector close to the in-
verse magnetic length. At large wave vector, neutral CD
waves excitations consist of pairs of fractionally charge
quasiparticles that are associated with the energy gaps of
the IQL. More recently, it was suggested that the strong
correlations between electrons are important in explain-
ing the structure observed in photoluminescence at v=1
and this state is considered to be a strongly correlated
state,2 similar to the incompressible states at fractional
filling factors. It was shown that the system always has
a gap, even when the single-particle gap vanishes (i.e.
when g=0), as a result of electron-electron repulsion. It
has also been shown' that, in that case when the elec-
tron Zeeman energy is large, the low energy states at
v=1 are the excitonic states in which the spin-t lowest
Landau level is filled and the valence band hole binds
with a single spin-4 electron to form an exciton. In an-
alyzing the PL spectra obtained from a 2 DEG in the
FQHE regime, the appearance of a doublet structure in
the photoluminescence (PL) spectrum4~7 around v=2/3
was interpreted by Apalkov and Rashba8 as an evidence
for the appearance of an indirect, single MR transition
from an extensive area in k space for keB=l (where tB
is the magnetic length). The formation of the rotonsis due to the reduction, at large wave vectors, of the
excitonic binding energy between the electron and the
hole." The MR minimum is a precursor to the gap
collapse associated with the Wigner crystal instability'
and is connected with the excitonic attraction between
fractionally charged quasiparticles. The calculations8 re-
ported for the case of the filling factor v=1/3 showed
that the dispersion of the excitons is strongly suppressed
by their coupling to the IQL and the lowest branch of
the exciton spectrum passes completely below the MR
spectrum. Another important result of note is the fact
that, even if its theoretical prediction is based on cal-
culations performed in the case of fractional filling fac-
tor v=1/3, the existence of the MR peak was observed
in the MPL, also at filling factors that do not involve
the FQHE.47 In addition, evidence of excitonic binding
and roton minima formation was found by Pinczuk et. al.
for the filling factors v>13 and v=1/314 from inelastic
light scattering studies performed on the 2DEG formed in
high-mobility GaAs structures. Karrai et.al.ls analyzed
the magneto-transmission spectra obtained from a quasi-
three-dimensional electron system subjected to a parallel
magnetic field and found evidence for the existence of a
MR excitation for a wide range of magnetic fields.
In this report, we present the results of MPL measure-
ments of a MBE grown high quality GaAs/Alo.3Gao.7As
single heterojunction (SHJ) with a dark electron den-
sity of 1.2x10"cm-2 and a mobility higher than
3x106cm2/Vs. In these experiments, during con-
stant laser illumination, the 2DEG density increased to
2.1x10"cm-2. The experimental layout for the PL mea-
surements has been described previously.'6 Using a quasi-
continuous magnet, the field was varied from 0 to 60 T,
while the temperature was changed from 1.5K to 45OmK.
The polarized spectra that we obtained showed the ap-
pearance of a doublet at filling factors v>3/2 and the per-
sistence of this effect to the highest magnetic fields uti-
lized. In Fig. 1 we show the unpolarized spectra obtained
at a temperature of 1.5K at the filling factor v=2, 3/2
and 1. The EO-hh peak that appears at v=5 (B=1.82T)1
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Kim, Yongmin; Munteanu, F. M.; Perry, C. H.; Reno, J. L.; Rickel, D. G. & Simmons, J. A. Photoluminescence Detected Doublet Structure in the Integer and Fractional Quantum Hall Regime, article, May 25, 1999; Albuquerque, New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc711192/m1/1/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.