120 research outputs found
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
Effect of zero energy bound states on macroscopic quantum tunneling in high-Tc superconductor junctions
The macroscopic quantum tunneling (MQT) in the current biased high-Tc
superconductor Josephson junctions and the effect of the zero energy bound
states (ZES) on the MQT are theoretically investigated. We obtained the
analytical formula of the MQT rate and showed that the presence of the ZES at
the normal/superconductor interface leads to a strong Ohmic quasiparticle
dissipation. Therefore, the MQT rate is noticeably inhibited in compared with
the c-axis junctions in which the ZES are completely absent.Comment: 4 pages, 1 figure, comment and reference about recent experiment
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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 YBa Cu O Josephson junctions coupled to an LC circuit
We investigate classical thermal activation (TA) and macroscopic quantum
tunneling (MQT) for a YBaCuO (YBCO) Josephson junction
coupled to an LC circuit theoretically. Due to the coupling between the
junction and the LC circuit, the macroscopic phase dynamics can be described as
the escape process of a fictitious particle with an anisotropic mass moving in
a two-dimensional potential. We analytically calculate the escape rate
including both the TA and MQT regime by taking into account the peculiar
dynamical nature of the system. In addtion to large suppression of the MQT rate
at zero temperature, we study details of the temperature dependece of the
escape rate across a crossover region. These results are in an excellent
agreement with recent experimental data for the MQT and TA rate in a YBCO
biepitaxial Josephson junction. Therefore the coupling to the LC circuit is
essential in understanding the macroscopic quantum dynamics and the qubit
operation based on the YBCO biepitaxial Josephson junctions.Comment: 13pages, 7 figures, 1 table, to appear in Phys. Rev. B 80 (2009
Persistent Currents in Quantum Chaotic Systems
The persistent current of ballistic chaotic billiards is considered with the
help of the Gutzwiller trace formula. We derive the semiclassical formula of a
typical persistent current for a single billiard and an average
persistent current for an ensemble of billiards at finite temperature.
These formulas are used to show that the persistent current for chaotic
billiards is much smaller than that for integrable ones. The persistent
currents in the ballistic regime therefore become an experimental tool to
search for the quantum signature of classical chaotic and regular dynamics.Comment: 4 pages (RevTex), to appear in Phys. Rev. B, No.59, 12256-12259
(1999
Structure analysis of the Ga-stabilized GaAs(001)-c(8x2) surface at high temperatures
Structure of the Ga-stabilized GaAs(001)-c(8x2) surface has been studied
using rocking-curve analysis of reflection high-energy electron diffraction
(RHEED). The c(8x2) structure emerges at temperatures higher than 600C, but is
unstable with respect to the change to the (2x6)/(3x6) structure at lower
temperatures. Our RHEED rocking-curve analysis at high temperatures revealed
that the c(8x2) surface has the structure which is basically the same as that
recently proposed by Kumpf et al. [Phys. Rev. Lett. 86, 3586 (2001)]. We found
that the surface atomic configurations are locally fluctuated at high
temperatures without disturbing the c(8x2) periodicity.Comment: 14 pages, 4 figures, 1 tabl
Observations on the morphological diversity and distribution of two siliceous nannoplankton genera, Hyalolithus and Petasaria
A pragmatic cognitive model for the interpretation of verbal–visual communication in television news programmes
The combination of the verbal and the visual track in television news discourse poses a considerable analytical challenge. In the viewers’ minds the co-habitation of these two semiotic channels triggers a complex network of inferential processes, based on expectations of coherence and relevance, with which they make sense of the representation of the world offered in the news. Through the analysis of a number of news items, this article considers the cognitive processes which viewers may activate when extracting meaning from the multimedial messages contained in television news. The analysis of news items from two British television networks offered by the authors traces the possible meanings that, it is assumed, become available to a potential, ‘idealised’ or ‘implied’ viewer, who accesses the information with some social and cultural knowledge of contemporary Britain. Building on existing studies, the article proposes a model for the classification of verbal–visual relations
Common Variants in a Novel Gene, FONG on Chromosome 2q33.1 Confer Risk of Osteoporosis in Japanese
Osteoporosis is a common disease characterized by low bone mass, decreased bone quality and increased predisposition to fracture. Genetic factors have been implicated in its etiology; however, the specific genes related to susceptibility to osteoporosis are not entirely known. To detect susceptibility genes for osteoporosis, we conducted a genome-wide association study in Japanese using ∼270,000 SNPs in 1,747 subjects (190 cases and 1,557 controls) followed by multiple levels of replication of the association using a total of ∼5,000 subjects (2,092 cases and 3,114 controls). Through these staged association studies followed by resequencing and linkage disequilibrium mapping, we identified a single nucleotide polymorphism (SNP), rs7605378 associated with osteoporosis. (combined P = 1.51×10−8, odds ratio = 1.25). This SNP is in a previously unknown gene on chromosome 2q33.1, FONG. FONG is predicted to encode a 147 amino-acid protein with a formiminotransferase domain in its N-terminal (FTCD_N domain) and is ubiquitously expressed in various tissues including bone. Our findings would give a new insight into osteoporosis etiology and pathogenesis
Association of the D repeat polymorphism in the ASPN gene with developmental dysplasia of the hip: a case-control study in Han Chinese
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