Plenarvorträge - DPG-Tagungen

Symposium Non-Fermi Liquids in Quantum Structures Donnerstag
Fachsitzungen
– Hauptvorträge –
SYNF 1 Non-Fermi Liquids in Quantum Structures
Zeit: Donnerstag 15:00–18:30 Raum: H 1
Hauptvortrag SYNF 1.1 Do 15:00 H 1
Coulomb Drag Between Quantum Wires: Beyond Tomonaga-
Luttinger Model — •Leonid Glazman — Theoretical Physics Institute,
University of Minnesota, Minneapolis, Minnesota 55455, USA
We demonstrate that in a wide range of temperatures, Coulomb drag
between two weakly coupled quantum wires is dominated by processes
with a small interwire momentum transfer. Such processes, not accounted
for in the conventional Luttinger liquid theory, contribute to drag only
because the electron dispersion relation is not linear. The corresponding
contribution to the drag resistance scales with temperature as T 2 if the
wires are identical, and as T 5 if the wires are different.
Hauptvortrag SYNF 1.2 Do 15:35 H 1
Spin and Charge Separation and Localization in One - Dimension
Measured Using Momentum Resolved Tunneling — •Amir
Yacoby — Department of Condensed Matter Physics, Weizmann Institute
of Science, Rehovot 76100, Israel
We have measured the collective excitation spectrum of interacting
electrons in one-dimension. The experiment consists of controlling the
energy and momentum of electrons tunneling between two clean and
closely situated, parallel quantum wires in a GaAs/AlGaAs heterostructure
while measuring the resulting conductance. At high elelctron densities
the measured excitation spectrum clearly deviates from the noninteracting
spectrum, attesting to the importance of Coulomb interactions.
Notable is the observation of two excitation branches corresponding
to spin - charge separation. In short wires, 6 microns and 2 microns long,
finite size effects, resulting from breaking of translational invariance, are
observed. Here spin and charge separation is manifested through Moire
patterns generated from the spin and charge excitation velocities. At low
electron densities the system abruptly looses translation invariance and
becomes localized. We find that the localization length corresponds to
the inter-electron spacing determined by the 1D electron density.
Hauptvortrag SYNF 1.3 Do 16:10 H 1
Probing spin-charge separation in tunnel-coupled parallel quantum
wires — •M. Governale 1 and U. Zülicke 2 — 1 Scuola Normale
Superiore, piazza dei Cavalieri 7, I-56100 Pisa, Italy — 2 Institute of Fundamental
Sciences, Massey University, Private Bag 11222, Palmerston
North, New Zealand
Interactions in one-dimensional electron systems are expected to cause
a dynamical separation of electronic spin and charge degrees of freedom.
This non-Fermi liquid phenomenon, called spin-charge separation,
manifests itself as a double peak structure in the single-electron spectral
function, and can be detected by momentum-resolved tunneling spectroscopy.
A promising setup consists of two quantum wires coupled by
an extended uniform tunnel barrier[1].
We consider a minimal model for one-dimensional interacting electrons
exhibiting spin-charge separation, where we neglect interactions between
electrons with opposite chirality. We present results for the differential
tunneling conductance and we discuss the features arising from spincharge
separation. Furthermore, we provide a theoretical framework to
go beyond the perturbative treatment of tunneling, and we calculate the
density-density response function[2].
[1] O. M. Auslander, A. Yacoby, R. de Picciotto, K. W. Baldwin, L. N.
Pfeiffer, and K. W. West, Science 295, 825 (2002).
[2] U. Zülicke, and M. Governale, Phys. Rev. B 65, 205304 (2002).
Hauptvortrag SYNF 1.4 Do 16:45 H 1
A carbon nanotube quantum dot coupled to superconductors
— •Mark Buitelaar 1,2 , Bakir Babic 2 , Wolfgang Belzig 2 ,
Christoph Bruder 2 , Thomas Nussbaumer 2 , and Christian
Schönenberger 2 — 1 Cavendish Laboratory, Madingley Road, CB3
0HE, Cambridge, United Kingdom — 2 Institut für Physik, Universität
Basel, Klingelbergstrasse 82, CH 4056 Basel, Switzerland
The electron spin is of central importance in two of the most widely
studied many-body phenomena in solid-state physics: the Kondo effect
and superconductivity. We have investigated their mutual interplay at
the level of a single spin in a carbon nanotube quantum dot. The quantum
dot can be changed from a non-Kondo to a Kondo system as the
number of electrons on the dot is changed from even to odd. We demonstrate
that the Kondo correlations on the dot are not destroyed by the
superconductivity if the Kondo temperature, which varies for different
single-electron states, exceeds the superconducting gap energy.
We observe multiple Andreev reflection peaks in the differential conductance.
The position and magnitude of the subharmonic gap structure
is found to depend strongly on the level positions of the single-electron
states which are adjusted with a gate electrode. A theoretical model of
the device reproduces some of the key features of the experimental data.
Hauptvortrag SYNF 1.5 Do 17:20 H 1
Dimensional crossover and deconfinement in Bechgaard salts
— •Thierry Giamarchi — DPMC, University of Geneva, 24 Quai
Ernest-Ansermet, CH-1211 Geneva, Switzerland
The Bechgaard salts are made of weakly coupled one dimensional
chains. This particular structure gives the possibility to observe in these
systems a dimensional crossover between a high temperature (or high
energy) one dimensional phase and a two or three dimensional system.
Since the filling of the chains is commensurate the system thus undergoes
a deconfinement transition from a one dimensional Mott insulator
to a two (or three) dimensional metal. Such a transition has of course
a strong impact on the physical properties of these compounds, and is
directly seen in transport measurements.
In order to describe such a transition a dynamical mean field method
has been introduced (chain-DMFT). Using this method we investigate
a system of coupled Hubbard chains and show that we can indeed reproduce
the deconfinement transition. This allows to determine physical
quantities such as the transport transverse to the chains and the shape
of the Fermi surface and quasiparticle residues in the low temperature
phase. The consequences for the Bechgaard salts are discussed.
Hauptvortrag SYNF 1.6 Do 17:55 H 1
Spectroscopic signatures of spin-charge separation in a quasione-dimensional
organic conductor — •Ralph Claessen — Experimentalphysik
II, Universität Augsburg, D-86135 Augsburg
In interacting one-dimensional (1D) metals conventional Fermi liquid
behavior is expected to break down due to a dynamical decoupling of
charge and spin degrees of freedom. Angle-resolved photoelectron spectroscopy
(ARPES) on the electronic structure of the quasi-1D organic
conductor TTF-TCNQ [1] indeed reveals significant discrepancies to
band theory. Instead, the experimental spectra can be well explained
by the 1D Hubbard model [2], which accounts for the intramolecular
Coulomb interaction and predicts signatures of spin-charge separation
over the entire conduction band width. The model description can even
be made quantitative, if one accounts for an enhanced hopping integral
at the surface related to a relaxation of the topmost molecular layer.
The importance of strong 1D correlation effects is further supported by
a remarkable temperature dependence of the ARPES data. These results
provide strong spectroscopic evidence for the occurence of spin-charge
separation in the finite energy physics of TTF-TCNQ. Deviations of the
Hubbard model description for the low-energy spectral behavior is attributed
to the neglect of interchain coupling, long-range Coulomb interaction
and/or electron-phonon coupling.
[1] R. Claessen et al., Phys. Rev. Lett. 88, 096402 (2002).
[2] M. Sing et al., Phys. Rev. B 68, 125111 (2003).