4,361 research outputs found
Thermally induced 0-pi phase transition in Josephson junctions through a ferromagnetic oxide film
We investigate the Josephson transport through a ferromagnetic oxide film,
e.g., LaBaCuO, theoretically. Using the recursive Green's function
technique, we found the formation of a pi-junction in such systems. Moreover
the 0-pi phase transition is induced by increasing the temperature. Such
ferromagnetic-oxide based Josephson junctions may become an element in the
architecture of future quantum computers.Comment: 4 pages, 3 figure
Effect of d-f hybridization on the Josephson current through Eu-chalcogenides
A superconducting ring with a pi junction made from
superconductor/ferromagnetic-metal/superconductor (S-FM-S) exhibits a
spontaneous current without an external magnetic field in the ground state.
Such pi ring provides so-called quiet qubit that can be efficiently decoupled
from the fluctuation of the external field. However, the usage of the FM gives
rise to strong Ohmic dissipation. Therefore, the realization of pi junctions
without FM is expected for qubit applications. We theoretically consider the
possibility of the pi coupling for S/Eu-chalcogenides/S junctions based on the
d-f Hamiltonian. By use of the Green's function method we found that pi
junction can be formed in the case of the finite d-f hybridization between the
conduction d and the localized f electrons.Comment: 4 pages, 4 figure
Two-dimensional macroscopic quantum dynamics in YBCO Josephson junctions
We theoretically study classical thermal activation (TA) and macroscopic
quantum tunneling (MQT) for a YBCO Josephson junction coupled with an LC
circuit. The TA and MQT escape rate are calculated by taking into account the
two-dimensional nature of the classical and quantum phase dynamics. We find
that the MQT escape rate is largely suppressed by the coupling to the LC
circuit. On the other hand, this coupling leads to the slight reduction of the
TA escape rate. These results are relevant for the interpretation of a recent
experiment on the MQT and TA phenomena in YBCO bi-epitaxial Josephson
junctions.Comment: 9 pages, 2 figure
Macroscopic quantum dynamics of pi-junctions with ferromagnetic insulators
We theoretically investigate the macroscopic quantum dynamics of a pi
junction with a superconductor (S) and a multiferroic material or a
ferromagnetic insulator (FI). By deriving the effective action from a
microscopic Hamiltonian, a pi-junction qubit (a S-FI-S superconducting quantum
interference device ring) is proposed. In this qubit, a quantum two-level
system is spontaneously generated and the effect of the quasiparticle
dissipation is found to be very weak. These features make it possible to
realize a quiet qubit with high coherency. We also investigate macroscopic
quantum tunneling (MQT) in current-biased S-FI-S pi junctions and show that the
influence of the quasiparticle dissipation on MQT is negligibly small.Comment: 4 pages, 2 figure
Theory of Macroscopic Quantum Tunneling in High-T_c c-Axis Josephson Junctions
We study macroscopic quantum tunneling (MQT) in c-axis twist Josephson
junctions made of high-T_c superconductors in order to clarify the influence of
the anisotropic order parameter symmetry (OPS) on MQT. The dependence of the
MQT rate on the twist angle about the c-axis is calculated by using
the functional integral and the bounce method. Due to the d-wave OPS, the
dependence of standard deviation of the switching current distribution
and the crossover temperature from thermal activation to MQT are found to be
given by and , respectively. We also show
that a dissipative effect resulting from the nodal quasiparticle excitation on
MQT is negligibly small, which is consistent with recent MQT experiments using
BiSrCaCuO intrinsic junctions. These results
indicate that MQT in c-axis twist junctions becomes a useful experimental tool
for testing the OPS of high-T_c materials at low temperature, and suggest high
potential of such junctions for qubit applications.Comment: 15 pages, 8 figures, 1 tabl
Theory of two-dimensional macroscopic quantum tunneling in a Josephson junction coupled with an LC circuit
We investigate classical thermal activation (TA) and macroscopic quantum
tunneling (MQT) for a Josephson junction coupled with an LC circuit
theoretically. The TA and MQT escape rate are calculated analytically by taking
into account the two-dimensional nature of the classical and quantum phase
dynamics. We find that the MQT escape rate is largely suppressed by the
coupling to the LC circuit. On the other hand, this coupling gives rise to
slight reduction of the TA escape rate. These results are relevant for the
interpretation of a recent experiment on the MQT and TA phenomena in grain
boundary YBCO Josephson junctions.Comment: 4 pages, 1 figure, Proceedings of LT2
Tunneling Hamiltonian description of the atomic-scale 0-pi transition in superconductor/ferromagnetic-insulator junctions
We show a perturbation theory of the Josephson transport through
ferromagnetic insulators (FIs). Recently we have found that the appearance of
the atomic scale 0-pi transition in such junctions based on numerical
calculations. In order to explore the mechanism of this anomalous transition,
we have analytically calculated the Josephson current using the tunneling
Hamiltonian theory and found that the spin dependent pi-phase shift in the FI
barrier gives the atomic scale 0-pi transition.Comment: 4 pages, 1 figure, to appear in Physica
Recent Developments in Parallelization of the Multidimensional Integration Package DICE
DICE is a general purpose multidimensional numerical integration package.
There can be two ways in the parallelization of DICE, "distributing random
numbers into workers" and "distributing hypercubes into workers". Furthermore,
there can be the combination of both ways. So far, we had developed the
parallelization code using the former way and reported it in ACAT2002 in
Moscow. Here, we will present the recent developments of parallelized DICE in
the latter way as the 2nd stage of our parallelization activities.Comment: 5 pages, 2 figures, Talk given at the X International Workshop on
Advanced Computing and Analysis Techniques in Physics Research, ACAT 2005,
DESY-Zeuthen, Germany, 22-27 May 200
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