2,513 research outputs found
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
Numerical study of pi-junction using spin filtering barriers
We numerically investigate the Josephson transport through ferromagnetic
insulators (FIs) by taking into account its band structure. By use of the
recursive Green's function method, we found the formation of the pi junction in
the case of the fully spin-polarized FI (FPFI), e.g., LaBaCuO.
Moreover, the 0-pi transition is induced by increasing the thickness of FPFI.
On the other hand, Josephson current through the Eu chalcogenides shows the pi
junction behavior in the case of the strong d-f hybridization between the
conduction d and the localized f electrons of Eu. Such FI-based Josephson
junctions may become a element in the architecture of future quantum
information devices.Comment: 9 pages, 5 figure
The Unique Type Ib Supernova 2005bf at Nebular Phases: A Possible Birth Event of A Strongly Magnetized Neutron Star
Late phase nebular spectra and photometry of Type Ib Supernova (SN) 2005bf
taken by the Subaru telescope at ~ 270 and ~ 310 days since the explosion are
presented. Emission lines ([OI]6300, 6363, [CaII]7291, 7324, [FeII]7155) show
the blueshift of ~ 1,500 - 2,000 km s-1. The [OI] doublet shows a doubly-peaked
profile. The line luminosities can be interpreted as coming from a blob or jet
containing only ~ 0.1 - 0.4 Msun, in which ~ 0.02 - 0.06 Msun is 56Ni
synthesized at the explosion. To explain the blueshift, the blob should either
be of unipolar moving at the center-of-mass velocity v ~ 2,000 - 5,000 km s-1,
or suffer from self-absorption within the ejecta as seen in SN 1990I. In both
interpretations, the low-mass blob component dominates the optical output both
at the first peak (~ 20 days) and at the late phase (~ 300 days). The low
luminosity at the late phase (the absolute R magnitude M_R ~ -10.2 mag at ~ 270
days) sets the upper limit for the mass of 56Ni < ~ 0.08 Msun, which is in
contradiction to the value necessary to explain the second, main peak
luminosity (M_R ~ -18.3 mag at ~ 40 days). Encountered by this difficulty in
the 56Ni heating model, we suggest an alternative scenario in which the heating
source is a newly born, strongly magnetized neutron star (a magnetar) with the
surface magnetic field Bmag ~ 10^{14-15} gauss and the initial spin period P0 ~
10 ms. Then, SN 2005bf could be a link between normal SNe Ib/c and an X-Ray
Flash associated SN 2006aj, connected in terms of Bmag and/or P0.Comment: 16 pages, 12 figures. Accepted by the Astrophysical Journa
Character of eigenstates of the 3D disordered Anderson Hamiltonian
We study numerically the character of electron eigenstates of the three
dimensional disordered Anderson model. Analysis of the statistics of inverse
participation ratio as well as numerical evaluation of the electron-hole
correlation function confirm that there are no localized states below the
mobility edge, as well as no metallic state in the tail of the conductive band.
We discuss also finite size effects observed in the analysis of all the
discussed quantities.Comment: 7 pages, 9 figures, resubmitted to Physical Review
Josephson pi-state in a ferromagnetic insulator
We predict anomalous atomic-scale 0-pi transitions in a Josephson junction
with a ferromagnetic-insulator (FI) barrier. The ground state of such junction
alternates between 0- and pi-states when thickness of FI is increasing by a
single atomic layer. We find that the mechanism of the 0-pi transition can be
attributed to thickness-dependent phase-shifts between the wave numbers of
electrons and holes in FI. Based on these results, we show that stable pi-state
can be realized in junctions based on high-Tc superconductors with
LaBaCuO barrier.Comment: 4 pages, 3 figures, Phys. Rev. Lett. (2010) in pres
Magnetic Ordering in V-Layers of the Superconducting System of Sr2VFeAsO3
Results of transport, magnetic, thermal, and 75As-NMR measurements are
presented for superconducting Sr2VFeAsO3 with an alternating stack of FeAs and
perovskite-like block layers. Although apparent anomalies in magnetic and
thermal properties have been observed at ~150 K, no anomaly in transport
behaviors has been observed at around the same temperature. These results
indicate that V ions in the Sr2VO3-block layers have localized magnetic moments
and that V-electrons do not contribute to the Fermi surface. The electronic
characteristics of Sr2VFeAsO3 are considered to be common to those of other
superconducting systems with Fe-pnictogen layers.Comment: 4 pages, 4 figures, To appear in JPSJ 79 (2010) 12371
SN 2006aj Associated with XRF 060218 At Late Phases: Nucleosynthesis-Signature of A Neutron Star-Driven Explosion
Optical spectroscopy and photometry of SN 2006aj have been performed with the
Subaru telescope at t > 200 days after GRB060218, the X-ray Flash with which it
was associated. Strong nebular emission-lines with an expansion velocity of v ~
7,300 km/s were detected. The peaked but relatively broad [OI]6300,6363
suggests the existence of ~ 2 Msun of materials in which ~1.3 Msun is oxygen.
The core might be produced by a mildly asymmetric explosion. The spectra are
unique among SNe Ic in (1) the absence of [CaII]7291,7324 emission, and (2) a
strong emission feature at ~ 7400A, which requires ~ 0.05 Msun of
newly-synthesized 58Ni. Such a large amount of stable neutron-rich Ni strongly
indicates the formation of a neutron star. The progenitor and the explosion
energy are constrained to 18 Msun < Mms < 22 Msun and E ~ (1 - 3) 10^{51} erg,
respectively.Comment: Accepted for Publication in the Astrophysical Journal Letters (2007,
ApJ, 658, L5). 8 pages, including 1 table and 3 figures. Typos correcte
Magnetoresistance of metallic perovskite oxide LaNiO
We report a study of the magnetoresistance (MR) of the metallic perovskite
oxide LaNiO as a function of the oxygen stoichiometry
( 0.14), magnetic field (H ) and temperature (1.5K T 25K). We find a strong dependence of the nature of MR on the oxygen
stoichiometry. The MR at low temperatures change from positive to negative as
the sample becomes more oxygen deficient (i.e, increases). Some of the
samples which are more resistive, show a resistivity minima at
20K. We find that in these samples the MR is positive at T >
and negative for T < . We conclude that in the absence of
strong magnetic interaction, the negative MR in these oxides can arise from
weak localisation effects.Comment: 10 pages in REVTeX format, 4 eps fig
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