Plenarvorträge - DPG-Tagungen

Halbleiterphysik Montag
HL 5.7 Mo 11:45 H14
Quantum Dots as Quantum Bits — •Daniel Schröer 1 , Andreas
K. Hüttel 1 , Stefan Ludwig 1 , Werner Wegscheider 2 , and
Jörg Kotthaus 1 — 1 CeNS und Sektion Physik der LMU München —
2 Institut für Angewandte und Experimentelle Physik der Universität Re-
gensburg
We create lateral quantum dots by depleting the two-dimensional electron
system of an AlGaAs/GaAs heterostructure with lithographically
defined Schottky gates. The advantage of this lateral approach is the
flexibility in number and orientation of leads and gates. Multiple quantum
dots can be coupled capacitively or via tunnel barriers. The coupling
strengths and the number of free charge carriers per dot are tuned by
means of gate voltages. A double quantum dot is often regarded as an
artificial molecule, as the discrete states of both dots split into molecular
bonding and antibonding states. These form a two-level system that is
applicable as a qubit for quantum information processing. The complexity
of the molecular states increases with the number of free electrons per
dot. Hence, we aim to reduce the dot sizes and integrate suitable tools to
read out the number of charge carriers (e.g. a quantum point contact).
The molecular states are probed by analysing the charging diagram of
the system. In addition we will attempt to couple more than two quantum
dots to study the interaction of several qubits. First results will be
presented.
HL 5.8 Mo 12:00 H14
Scattering Wavefunctions in Ballistic Rectifyers
— •Oliver Bendix, Ragnar Fleischmann, and Theo Geisel —
MPI für Strömungsforschung and Institut für Nichtlineare Dynamik, Universität
Göttingen, Bunsenstraße 10, 37073 Göttingen
Electron transport in mesoscopic systems in semiconductors with typical
length scales shorter than the mean free path can be assumed to
be ballistic. Recent experimental and theoretical work has revealed an
unexpected rectification effect based on ballistic transport in mesoscopic
cross-junctions with broken symmetry[1,2,3].
In our simplified model[2] a crucial role is played by the energydependence
of the number of current-carrying modes. In a more detailed
description this corresponds to the energy-dependence of the scattering
coefficients. Here we present numerical results for the scattering wavefunctions
in ballistic rectifyers.
HL 6 Photonische Kristalle I
[1] A. M. Song et al., PRL 80 (1998) 3831
[2] R. Fleischmann and T. Geisel, PRL 89 (2002) 16804
[3] S. de Haan et al., PRL (in press)
HL 5.9 Mo 12:15 H14
Preparation of curved two dimensional electron systems in
InGaAs-microtubes — •Stefan Mendach, Olrik Schumacher,
Christian Heyn, Holger Welsch, and Wolfgang Hansen — Institut
für Angewandte Physik, Universität Hamburg, Jungiusstrasse 11,
D-20355 Hamburg, Germany
We present a preparation method to realise transport measurements
on evenly curved two-dimensional electron systems (2 DESs). By
combining the method of self-rolling strained double-layers [1,2] with
a special lithographic procedure we are able to roll-in and contact
AlGaAs/GaAs/AlGaAs quantum well structures into tubes or curved
lamellas, respectively. Applying a magnetic field to such structures
results in a strong modulation with changing sign of the magnetic field
components perpendicular to the curved 2 DES plane. Our preparation
method allows transport measurements along or perpendicular to
this modulation. We present and discuss our first magneto-transport
measurements on such rolled 2 DESs.
[1] V. Ya. Prinz et al., Physica E6 (2000) 828-831.
[2] O.G. Schmidt, K. Eberl, Nature 410 (2001) 168.
HL 5.10 Mo 12:30 H14
Bosonization method for disordered and chaotic systems — •G.
Schwiete 1 , K. B. Efetov 1,2 , and K. Takahashi 1 — 1 Theoretische
Physik III, Ruhr-Universität Bochum, 44780 Bochum, Germany — 2 L.
D. Landau Institute for Theoretical Physics, 117940 Moscow, Russia
Using a supersymmetry formalism we derive a new supermatrix representation
of the generating functional for the problem of electron motion
in an external potential. Non-linear sigma models derived previously for
disordered systems can be obtained from this model using a coarse graining
procedure. As an example we treat smooth disorder in an infinite system.
As a new application, we consider scattering on strong impurities
for which the Born approximation cannot be used. Possible applications
to quantum chaotic systems and the interacting disordered electron gas
will be discussed.
Zeit: Montag 12:45–13:30 Raum: H15
HL 6.1 Mo 12:45 H15
Space-dependent optical and electronic properties of semiconductor
photonic-crystal structures — •B. Pasenow, M. Reichelt,
T. Meier, T. Stroucken, P. Thomas, and S.W. Koch
— Fachbereich Physik und Wissenschaftliches Zentrum für Materialwissenschaften,
Philipps-Universität, Renthof 5, D-35032 Marburg
The optical and electronic properties of a semiconductor heterostructure
are modified in the vicinity of a structured dielectric environment,
e.g., a photonic crystal [1-3]. In such structures the band gap and the
Coulomb interaction potential are space dependent, which results in a
spatial variation of the spectral position of the exciton resonance and its
binding energy [2]. Therefore one can create spatially non-homogeneous
carrier distributions by spectrally selective optical excitation [3]. Following
the excitation, the carrier distributions show initially an interesting
coherent wave packet dynamics, before they eventually approach an incoherent
thermal quasi-equilibrium distribution.
[1] T. Stroucken, R. Eichmann, L. Banyai, and S.W. Koch, J. Opt. Soc.
Am. B 19, 2292 (2002).
[2] R. Eichmann, B. Pasenow, T. Meier, T. Stroucken, P. Thomas, and
S.W. Koch, Appl. Phys. Lett. 82, 355 (2003).
[3] Semiconductor Optics in Photonic Crystal Structures, T. Meier and
S.W. Koch, to appear in Photonic Crystals - Advances in Design, Fabrication
and Characterization, Eds. K. Busch, S. Lölkes, R.B. Wehrspohn,
and H. Föll, Wiley, 2004.
HL 6.2 Mo 13:00 H15
Strongly localized discrete solitons in photonic crystal defect
chains — •Rumen Iliew, Christoph Etrich, Ulf Peschel, and
Falk Lederer — Inst. für Festkörpertheorie und Theoretische Optik,
Friedrich-Schiller-Univ. Jena, Max-Wien-Platz 1, 07743 Jena
We found strongly localized solitons in a linear chain of coupled point
defects embedded in a Kerr-type nonlinear photonic crystal.
The dynamics of such a coupled-resonator optical waveguide (CROW)
can be described in tight-binding approximation by a set of coupled
modal equations [1] which were shown to allow for strongly localized soliton
solutions [2]. To compare these results with the full system, for the
first time, to our knowledge, the temporal dynamics of localized excitations
is investigated in a two-dimensional (2D) nonlinear photonic crystal
by employing 2D TM finite-difference time-domain simulations including
Kerr-nonlinearity. Our model system is a 2D hexagonal photonic crystal
with a TM photonic band gap in the linear regime where a chain
of point-defects was embedded. Depending on the pump parameters we
found strongly localized solitons in the nonlinear regime at frequencies
below the miniband, as predicted by the tight-binding approach.
We will present results of FDTD simulations and compare them against
the results obtained from the modal equations.
[1] D. N. Christodoulides and N. K. Efremidis, Opt. Lett. 27, 568 (2002).
[2] F. Lederer, S. Darmanyan, and A. Kobyakov, Spatial Solitons,
Springer Series in Optical Science 82, S. Trillo and W. E. Torruellas
(eds.), (Springer-Verlag New York 2001), pp. 269–292.
HL 6.3 Mo 13:15 H15
Tuneable Opals — •A. von Rhein 1 , T. Kramer 2 , T. Roeder 2 ,
K. Huber 2 , and S. Greulich-Weber 1 — 1 University of Paderborn,
Fakulty of Science, Physics Department, D-33098 Paderbron, Germany
— 2 University of Paderborn, Fakulty of Science, Chemistry Department,
D-33098 Paderbron, Germany
Photonic crystals already have been realized thru a wide range of methods.
In particular nature has developed a selfassembling technique of creating
photonic crytals. Nanospheres of about 200-400 nm diameter build