Plenarvorträge - DPG-Tagungen

Symposium Quantum Shot Noise in Nanostructures Montag
Hauptvortrag SYSN 2.2 Mo 16:30 H1
Full Counting Statistics of Multiple Andreev Reflections
— •Juan Carlos Cuevas — Institut für Theoretische
Festkörperphysik,Universität Karlsruhe, D-76128 Karlsruhe
The complete understanding of the electronic transport in mesoscopic
systems requires information that goes beyond the analysis of the current.
In this sense, the ultimate goal is the determination of the full
current distribution. In the context of superconductivity the basic situation,
in which this full distribution had not been yet investigated, is
a point contact between two superconductors out of equilibrium, where
the transport properties at subgap voltages are dominated by multiple
Andreev reflections (MAR).
In this talk I will present our recent results, which demonstrate that
in superconducting contacts at finite voltage the charge transport is described
by a multinomial distribution of multiple charge transfers. This
proves that in the MAR processes the charge is transmitted in large
quanta. We have obtained analytically the MAR probabilities, from which
all transport properties are easily computed. Our result constitutes the
culmination of the recent progress in the understanding of MARs, which
are a key concept in mesoscopic superconductivity.
SYSN 2.3 Mo 17:00 H1
Shot noise in resonant single electron tunneling through InAs
quantum dots — •Frank Hohls 1 , André Nauen 1 , Niels Maire 1 ,
Rolf Haug 1 , and Klaus Pierz 2 — 1 Institut für Festkörperphysik, Universität
Hannover, D-30167 — 2 Physikalisch-Technische Bundesanstalt,
Bundesallee 100,
We investigate the noise properties of resonant single electron transport
through self-assembled InAs quantum dots which are embedded in
the AlAs barrier of a GaAs-AlAs-GaAs tunneling device. Due to their
small size (diameter 10-15 nm and height 3 nm) these quantum dots
display both strong size quantization and Coulomb blockade. Thus the
tunneling current through our device is given by resonant single electron
tunneling through the ground state of the quantum dot.
The measured noise spectrum of the current is dominated by frequencyindependent
shot noise for frequencies above 1 kHz. As expected for single
electron tunneling the spectral noise power S is suppressed in comparison
to the full Poissonian shot noise 2eI observed for single barrier tunneling.
We observe a linear voltage dependence of the suppression α = S/2eI
which can be related to the dimensionality of the source contacts. At the
onset of the resonant current we observe additional features which are
probably caused by a correlation effect between dot and lead known as
fermi edge singularity.
SYSN 2.4 Mo 17:15 H1
Shot noise of coherent tunneling through Coulomb interacting
quantum dots — •G. Kießlich, A. Wacker, and E. Schöll —
Institut für Theoretische Physik, TU Berlin, Hardenbergstr. 36, 10623
Berlin
The spectral power density of the tunneling current through quantum
dots can help to clarify the transition from sequential (particlelike) to
coherent (wavelike) mesoscopic transport. In the high temperature limit
kBT ≫ Γ (Γ is the linewidth of the resonant quantum dot level) the
noise and the current are well described by sequential tunneling using
a Pauli master equation approach [1] which is in good agreement with
experimental data [2]. For intermediate temperatures kBT ≃ Γ we derive
the noise behavior starting from the Anderson Hamiltonian using a
nonequilibrium Green’s function technique. In this framework we treat
the tunneling coupling to the reservoirs exactly, and the Coulomb interaction
in the quantum dot is included perturbatively beyond the Hartree
approximation. The effect of Coulomb repulsion on the bias dependence
of the noise in the sequential and coherent regime will be shown in detail.
[1] G. Kießlich, A. Wacker, and E. Schöll, Phys. Rev. B 68, 125320 (2003)
[2] G. Kießlich, A. Wacker, E. Schöll, A. Nauen, F. Hohls, and R.J. Haug,
Phys. Status Solidi C 0, 1293 (2003)
SYSN 2.5 Mo 17:30 H1
Frequency Dispersion in Full Counting Statistics — •Sebastian
Pilgram 1 , Kirill Nagaev 2 , and Markus Büttiker 1 —
1 Département de Physique Théorique, Université de Genève, CH-1211,
Genève, Switzerland — 2 Institute of Radioengineering and Electronics,
Russian Academy of Sciences, Mokhovaga ulica 11, 125009 Moscow,
Russia
Transport of electrons through disordered mesoscopic conductors is
considered in the semiclassical regime. We express the full transport
statistics of current in terms of a stochastic path integral. In the semiclassical
limit, this path integral may be evaluated in the saddle point
approximation. The formalism is used to study the frequency dispersion
of higher order correlation functions. Investigating both ballistic cavities
and diffusive wires, we find surprisingly that the third cumulant of
full current statistics shows a low-frequency dispersion which is absent
in noise correlators. This dispersion is associated with charge neutral
fluctuations of the electron occupation function and exists in the regime
of non-interacting electrons as well as in the presence of strong electronelectron
scattering (Reference: K.E. Nagaev, S. Pilgram, and M. Buttiker,
cond-mat/0306465).