Plenarvorträge - DPG-Tagungen

Halbleiterphysik Dienstag
HL 14 Symposium Quanten-Hall-Systeme
Zeit: Dienstag 10:15–13:15 Raum: H15
HL 14.1 Di 10:15 H15
Radiation induced zero-resistance states in high mobility
GaAs/AlGaAs devices — •Ramesh Mani — Harvard University,
Gordon McKay Laboratory of Applied Science, 9 Oxford Street, Cambridge,
MA 02138 USA — Max-Planck-Institut FkF, Heisenbergstr. 1,
70569 Stuttgart, Germany
We report the experimental detection of novel zero-resistance states [1],
which are induced by electromagnetic wave excitation in ultra high mobility
GaAs/AlGaAs heterostructure devices including a two-dimensional
electron system. Radiation-induced vanishing-resistance states, which do
not exhibit concomitant Hall resistance quantization, are demonstrated
in the large filling factor, low magnetic field limit, at liquid helium temperatures.
It is shown that the observed resistance minima follow the
series B = [4/(4j+1)] Bf with j=1,2,., where Bf = 2pfm*/e, m* is an
effective mass, e is electron charge, and f is the radiation frequency. The
dependence of the effect is reported as a function of experimental parameters
such as the electromagnetic wave frequency, incident power,
temperature, and the current.
HL 14.2 Di 10:45 H15
Oscillatory photoconductivity of a 2D electron gas in magnetic
field — •D.G. Polyakov 1 , I.A. Dmitriev 1 , M.G. Vavilov 2 ,
I.L. Aleiner 3 , and A.D. Mirlin 1,4 — 1 Institut für Nanotechnologie,
Forschungszentrum Karlsruhe, 76021 Karlsruhe — 2 Physics Dept.,
Massachusetts Institute of Technology, Cambridge, MA 02139, USA —
3 Physics Dept., Columbia University, New York, NY 10027, USA —
4 Institut für Theorie der kondensierten Materie, Universität Karlsruhe,
76128 Karlsruhe
An intriguing development in the study of magnetotransport in highmobility
2DEGs was the observations by Zudov et al. and by Mani et
al. of magnetooscillations of the photoconductivity, evolving with increasing
microwave power into zero-resistance states. We discuss the
nature of the oscillations and develop theory which is in good agreement
with the experimental data. The most important mechanism of
the oscillations [1,2] is related to a radiation-induced change of the
electron distribution function. We consider nonlinear effects, with respect
to both the dc field and the microwave power, as well as the
temperature dependence due to the inelastic relaxation. We also study
[3] the oscillations governed by quasiclassical memory effects. For low
B, this mechanism, in combination with microwave-dependent screening,
may dominate over that based on the Landau quantization. [1]
I.A.Dmitriev, A.D.Mirlin, and D.G.Polyakov, cond-mat/0304529; [2]
I.A.Dmitriev, M.G.Vavilov, I.A.Aleiner, A.D.Mirlin, and D.G.Polyakov,
cond-mat/0310668; [3] I.A.Dmitriev, A.D.Mirlin, and D.G.Polyakov, to
be published.
HL 14.3 Di 11:15 H15
Optical Probe of Fractionally-Charged Quasiholes — •C.
Schüller 1 , K.-B. Broocks 1 , P. Schröter 1 , Ch. Heyn 1 , D. Heitmann
1 , T. Chakraborty 2 , V. M. Apalkov 3 , M. Bichler 4 , and
W. Wegscheider 5 — 1 Institut für Angewandte Physik, Universität
Hamburg — 2 Institute for Mathematical Sciences, Chennai, India —
3 University of Utah, Salt Lake City, USA — 4 Walter-Schottky-Institut,
Garching — 5 Institut für Experimentelle und Angewandte Physik,
Universität Regensburg
We perform optical experiments on dilute two-dimensional electron
systems (2DES) at very low temperatures (T < 0.1 K) and high magnetic
fields [1]. In photoluminescence experiments on a 2DES subjected
to a quantizing magnetic field around ν = 1/3, we have observed an
anomalous dispersion of the charged excitons [2]. We have found that
the anomaly exists only at a very low temperature (0.1 K) and an intermediate
electron density (0.9 × 10 11 cm −2 ). It is explained to occur
due to the perturbation of the incompressible liquid at ν = 1/3. The
perturbation is induced by the close proximity of a localized charged exciton
which creates a fractionally-charged quasihole in the liquid [3]. The
intruiging experimentally observed puzzle that the anomaly (2 meV) can
be destroyed by applying a small thermal energy of ∼ 0.2 meV is thereby
resolved, as this energy is enough to close the quasihole energy gap. This
work presents a probe of the quasihole gap in a quantum Hall system.
[1] C. Schüller et al., Phys. Rev. B 65, 081301(R) (2002).
[2] K.-B. Broocks et al., Phys. Rev. B 66, 041309(R) (2002).
[3] C. Schüller et al., Phys. Rev. Lett. 91, 116403 (2003).
HL 14.4 Di 11:45 H15
Coulomb Drag as a Probe of the Nature of Compressible States
in a Magnetic Field — •Sjoerd Lok 1 , K. Muraki 1 , S. Kraus 1 ,
W. Dietsche 1 , K. Von Klitzing 1 , D. Schuh 2 , M. Bichler 2 , and
W. Wegscheider 2 — 1 Max Planck Insitut für Festkörperforschung,
Heisenbergstrasse 1 70569 Stuttgart — 2 Walter Schottky Insitut, Technische
Universität München, Am Coulomb Wall, 85748 Garching
Magneto-drag reveals the nature of compressible states and the underlying
interplay of disorder and interactions. At filling factor 3/2 a clear
T 4/3 dependence is observed, which signifies the metallic nature of the
N=0 Landau level. In contrast, drag in higher Landau levels reveals an
additional contribution, which anomalously grows with decreasing T before
turning to zero following a thermal activation law. The anomalous
drag is discussed in terms of electron-hole asymmetry arising from disorder
and localization, and the crossover to normal drag at high fields as
due to screening of disorder.
HL 14.5 Di 12:15 H15
Coulomb drag in high Landau levels — •von Oppen Felix 1,2 ,
Mirlin A.D. 3,4 , and Gornyi I.V. 3 — 1 Inst. f. Theor. Physik, FU
Berlin, Arnimallee 14, 14195 Berlin — 2 Dept. of Cond. Matter Physics,
Weizmann Inst. of Science, Rehovot, Israel — 3 Inst. f. Nanotechnologie,
FZ Karlsruhe, 76021 Karlsruhe — 4 Inst. f. Theorie der Kond. Materie,
Uni Karlsruhe, 76128 Karlsruhe
Coulomb drag between two parallel two-dimensional electron systems
provides insight that is complementary to conventional transport measurements.
Recent experiments [1] found several surprises in Coulomb
drag in strong magnetic fields, in the limit of high Landau level filling
factor, including negative drag and an anomalous temperature dependence.
In this talk, we present a theory of Coulomb drag in high Landau
levels which is perturbative in the interlayer interaction and treats disorder
within the framework of the self-consistent Born approximation. We
show that in the experimentally relevant ballistic regime, there are several
contributions to Coulomb drag which differ parametrically but are
numerically of comparable magnitude in typical experiments. One class
of contributions is associated with the breaking of particle-hole symmetry
by the Landau-level density of states, while another, more conventional,
contribution arises from the breaking of this symmetry by the curvature
of the electron dispersion. We show that the interplay of these contributions
allows for a qualitative understanding of many features of the
existing experiments.
[1] J.G.S. Lok et al., Phys. Rev. B 63, 041305 (2001); K. Muraki et al.,
cond-mat/0311151 (2003).
HL 14.6 Di 12:45 H15
Momentum resolved tunnel spectroscopy: Investigating interactions
at quantum Hall edges — •Matthew Grayson und Matthew
Grayson — Walter Schottky Institut, Tech. Univ. Muenchen
We present experimental results on magneto-tunneling between a single
quantum Hall (QHE) edge and an orthogonal high-mobility twodimensional
contact in a T-shaped quantum well configuration. Simultaneous
conservation of energy E and canonical momentum k parallel to
the QHE edge allows us to directly probe the E vs. k dispersion relation
of individual integer QHE edge channels with excitation energies up to
100 meV. At high voltages, screening in the QHE edge is found to significantly
distort the dispersion relation in a fashion that is in excellent
agreement with Hartree calculations of the real-space edge potential. At
low voltages of order the Coulomb interaction energy, we find evidence for
an exchange-enhanced spin splitting of the integer quantum Hall effect
edge.