Plenarvorträge - DPG-Tagungen

Tiefe Temperaturen Montag
TT 8.25 Mo 14:30 Poster A
Microwave absorption of BSCCO based intrinsic Josephson
junctions — •Denis Vassioukov, Huabing Wang, Vyacheslav
Dremov, Yury Koval, and Paul Müller — Friedrich-Alexander
Universität Erlangen-Nürnberg
Recently, Wang et al. introduced a new sample fabrication method -
the so called double side technique. This sample geometry has unique
properties. It is possible to perform 4-point measurements and also to
avoid a big pedestal of BSCCO single crystal which usually occurs in
mesa-like structures. Using a combination of electron beam lithography
and photolithography, we were able to prepare stacks with minimum cross
sections down to 0.5 µ x 0.5 µ. These structures were imbedded into bowtie
antennas equipped with low pass filters for DC supply. We present
experimental data on microwave absorption in the step-like structures
at frequencies from 760 GHz to 2.5 THz. It is shown that the choice of
structure design is very crucial to the absorption properties of junctions
in the stack. Clear Shapiro steps were observed at positions according to
the Josephson relation.
TT 8.26 Mo 14:30 Poster A
Kollektives und statistisches Schaltverhalten von intrinsischen
Josephsonkontakten an TBCCO-Mikrobrücken auf
20 ◦ vicinal geschnittenem LaAlO3 — •Michael Mans, Jens
Scherbel und Paul Seidel — Institut für Festkörperphysik,
Friedrich-Schiller-Universität Jena, Helmholtzweg 5, 07743 Jena
In einem 2-stufigen Prozeß wurden TBCCO(2212)-Schichten hergestellt.
Ein amorpher Ba-Ca-Cu-O Precurser wird mittels RF-Sputtern bereitgestellt,
um ihn im Anschluß durch Oxythallination zu TBCCO umzukristallisieren.
Auf 20 ◦ vicinal geschnittenen LaAlO3-Substraten kristallisiert
das TBCCO so, daß seine CuO-Ebenen geneigt zur Substratnormalen
aufwachsen. Somit können planare Mikrobrücken gefertigt werden,
die intrinsische Josephsoneffekte zeigen und gut in Mikrowellenstrukturen
integrierbar sind. Die Strom-Spannungs-Kennlinien zeigten bis 70K
multiple Aststrukturen mit IC-Werten weniger µA und Normalleitungswiderständen
einiger kΩ. Das Schalten vom supraleitenden in den resistiven
Zustand wurde für die ersten resistiven Äste statistisch untersucht. In
bestimmten Fällen wurde ein kollektives Schaltverhalten mehrerer intrinsischer
Josephsonkontakte beobachtet. Die Standardabweichung der IC-
Verteilung ist um so geringer je mehr Kontakte zum jeweiligen Übergang
beitragen. Untersuchen zur Mikrowellenabsorption bei 100 GHz zeigten
ein mit wachsender Mikrowellenleistung sukzessives Aufspalten des kollektiven
Übergangs vom supraleitenden zum resistiven Zustand in multiple
Aststrukturen. Diese Dynamik läßt auf eine Kopplung der einzelnen
Josephsonkontakte mit ihren nächsten Nachbarn schließen.
TT 8.27 Mo 14:30 Poster A
Low Tc Josephson Junction response to an ultrafast laser pulse
— •Procolo Lucignano 1,2 , Arturo Tagliacozzo 1,2 , and Giacomo
Rotoli 1,3 — 1 Dipartimento di Scienza Fisiche, Universitá Federico
II Napoli, via Cinthia 80126 Napoli, Italy — 2 Coherentia INFM,
Italy — 3 Dipartimento di Energetica, Universitá di L’Aquila, Localitá
Monteluco, 67040 L’Aquila, Italy
We study the perturbation on the Josephson current induced when one
of the superconducting contacts is exposed to a single ultrafast laser pulse
radiation. Released energy is so small and the pulse duration so short
that coherence is not degradated. Relaxation properties and nonequilibrium
effect of the irradiated contact are taken into account within the
framework of a quasiclassical time dependent Keldysh formalism [1]. The
classical dynamics of a Josephson irradiated junction is simulated numerically
using our analytical results as source term. The switching out of
the zero voltage state can be easily controlled by tuning the laser light
intensity [2].
[1] W. Belzig, F.K. Wilhelm, G. Schön, C. Bruder, and A.D. Zaikin, Superlattices
and Microstructures 25, 1251-1288 (1999) and J. Rammer,H.
Smith, Rev. Mod. Phys., 58, 323,(1986)
[2] P. Lucignano, F.J. Hekking, A. Tagliacozzo in Proceedings of MQC2
ed. A. Legget, P. Silvestrini, B. Ruggiero, and preprints
TT 8.28 Mo 14:30 Poster A
Spectroscopic Measurements on Discrete Breathers in Josephson
ladders — •M. Schuster and A.V. Ustinov — Physikalisches
Institut III, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erwin-
Rommel-Straße 1, 91058 Erlangen
We experimentally study the transmission of electromagnetic radiation
through time-periodic localized excitations (discrete breathers, DB)
in one-dimensional arrays of Josephson junctions (Josephson ladders).
The experiments are motivated by the recent theoretical prediction of
Fano resonances with discrete breathers [1]. In experiment, we create
radiation by forcing one of the array junctions to a rotation frequency
(corresponding to a finite voltage) which is in resonance with the electromagnetic
modes of the lattice. Radiation is detected by a tunnel junction
detector at the opposite boundary of the array. We create the DB states
by local currents and study the radiation transmission through the ladder
as a function of DB frequency. We compare experimental data to
numerical simulations of the DB transmission properties.
[1] S. Flach, A. E. Miroshnichenko, V. Fleurov, and M. V. Fistul,
Phys. Rev. Lett. 90, 084101 (2003).
TT 8.29 Mo 14:30 Poster A
Guided vortex motion in Nb films on facetted substrate surfaces
— •Oleksiy K. Soroka1 , Michael Huth2 , Valerij A.
Shklovskij3 , Jens Oster1 , and Hermann Adrian1 — 1Institute of Physics, Johannes Gutenberg-University, Staudinger Weg 7, D-55099
Mainz, Germany — 2Institute of Physics, Johann Wolfgang Goethe-
University, Robert-Mayer-Str. 2-4, D-60054 Frankfurt/M., Germany —
3Kharkov State University, Physical Department, 4 Svobody Sq.,61077,
Kharkov, Ukraine
In the case of anisotropy of the viscous damping force in superconductors
a guided motion of vortices can take place. This means there exists
a preferred direction for the vortices to move in such superconductors.
Guided vortex motion leads to the appearance of new components in
the galvanomagnetic properties of the sample. One can observe an additional
odd magnetoresistive component with respect to magnetic field
reversal. Furthermore, an even contribution to the transverse (Hall) voltage
emerges.
Guided motion of vortices in Nb films on facetted α-Al2O3 (10¯10) was
observed by measuring the longitudinal and transversal resistivities of
the sample. The thin film sample consisted of five microbridges oriented
at the angles 0◦ , 30◦ , 45◦ , 60◦ and 90◦ with respect to the facet ridges.
Field inversion was used to separate the even and odd components of the
measured magnetoresistivities to obtain the contributions caused by the
guided vortex motion. The guiding angle was measured for the different
current orientations. Anomalous Hall effect, i.e. the sign reversal of the
Hall resistivity was found.
TT 8.30 Mo 14:30 Poster A
Ultra fast magneto-optics on BSCCO single crystals — •Björn
Biehler, Bernd-Uwe Runge, and Paul Leiderer — Universität
Konstanz, Universitätsstr. 10, 78457 Konstanz, Germany
We used the Faraday effect together with ultra short laser pulses to
investigate the dynamics in superconductors down to the nanosecond
regime. The lateral resolution is better than 10µm. Using this technique
we investigated flux penetration into various materials upon sudden heating
with a fs-laser pulse.
Under certain conditions thin superconducting films show a dendritic
instability when heated locally by a laser pulse [1]. Since BSCCO single
crystals have less pinning centers than typical thin films we chose this material
to compare its behaviour with different thin film systems (YBCO,
MgB2). Systematic variation of the experimental parameters did not lead
to dendrite nucleation, which makes it a unique system not showing this
instability.
[1] U. Bolz, B. Biehler, D. Schmidt, B.-U. Runge, P. Leiderer, Europhys.
Lett. 64(4) 517 (2003)
TT 8.31 Mo 14:30 Poster A
Magnetooptische Untersuchung des radiofrequenzinduzierten
Übergangs in die Normalleitung eines YBa2Cu3O7−x-Films
— •Simon Che’Rose 1 , Andreas Heinrich 1 , Bernd Stritzker
1 , Alois Hiebl 2 , Kai Numssen 2 und Helmut Kinder 2 —
1 Experimentalphysik IV, Universität Augsburg, 86135 Augsburg — 2 TU
München, Physik-Department E10, 85747 Garching
YBCO-Filme bieten ideale Eigenschaften für den Einsatz als passive
oder aktive Schalter. Das Schalten, also der Übergang in die Normalleitung,
kann dabei z.B. durch Erhöhung des anliegenden Stroms (passives
Schalten) oder aktiv durch einen thermischen Puls bzw., wie kürzlich gezeigt
werden konnte, durch Einkopplung eines radiofrequenten (RF) Pulses
(10-100MHz) erreicht werden. Im Gegensatz zum thermisch gepulsten
Schalten ist die physikalische Ursache des RF-induzierten Übergangs
noch nicht geklärt. Wir präsentieren in dieser Arbeit Ergebnisse der magnetooptischen
Untersuchungen zum RF-induzierten Schalten diverser