300 research outputs found
NMR relaxation time around a vortex in stripe superconductors
Site-dependent NMR relaxation time is calculated in the vortex
state using the Bogoliubov-de Gennes theory, taking account of possible
"field-induced stripe'' states in which the magnetism arises locally around a
vortex core in d-wave superconductivity. The recently observed huge enhancement
below at a core site in TlBaCuO is
explained. The field-induced stripe picture explains consistently other
relevant STM and neutron experiments.Comment: 4 pages, 4 figure
Vortex Structure in Superconducting Stripe States
The vortex structure in superconducting stripe states is studied according to
the Bogoliubov-de Gennes theory on the two-dimensional Hubbard model with
nearest-neighbor sites pairing interaction. The vortex is trapped at the
outside region of the stripe line, where the superconductivity is weak. The
superconducting coherence length along the stripe direction becomes long. There
are no eminent low-energy electronic states even near the vortex core. These
characters resemble the Josephson vortex in layered superconductors under a
parallel field.Comment: LaTeX 5 pages (using jpsj macros) with 3 figure
Induced Kramer-Pesch-Effect in a Two Gap Superconductor: Application to MgB2
The size of the vortex core in a clean superconductor is strongly temperature
dependent and shrinks with decreasing temperature, decreasing to zero for T ->
0. We study this so-called Kramer-Pesch effect both for a single gap
superconductor and for the case of a two gap superconductor using parameters
appropriate for Magnesium Diboride. Usually, the Kramer-Pesch effect is absent
in the dirty limit. Here, we show that the Kramer-Pesch effect exists in both
bands of a two gap superconductor even if only one of the two bands is in the
clean limit and the other band in the dirty limit, a case appropriate for MgB2.
In this case an induced Kramer-Pesch effect appears in the dirty band. Besides
numerical results we also present an analytical model for the spatial variation
of the pairing potential in the vicinity of the vortex center that allows a
simple calculation of the vortex core radius even in the limit T -> 0.Comment: 12 pages, 12 figure
Fermi Arc of Metallic Diagonal Stripes in High Tc Cuprates
Spectral weight is investigated for metallic diagonal stripe state in two
dimensional Hubbard model, and Fermi arc observed by angle-resolved
photoemission spectroscopy on LSCO is discussed. The Fermi arc coming from the
mid-gap state of diagonal stripe appears near
and equivalent position in the reciprocal space, and the gap opens below the
mid-gap state. We show how these spectral weight structure depends on the
phasing of stripes, i.e., site-centered or bond-centered stripes.Comment: 4 figure
Superconducting Gap Modulation in Weak Stripe States
The superconducting gap modulation is investigated in the presence of a weak
stripe structure, using the Bogoliubov-de Gennes theory on the two-dimensional
Hubbard model with nearest-neighbor site pairing interaction. We calculate the
local density of states and discuss the recently observed scanning tunneling
spectroscopy spectra with four lattice periodicity on Bi_2 Sr_2 Ca Cu_2
O_{8+delta} We also consider the spectral weight in the reciprocal space, where
the Fermi surface and the superconducting gap are modulated by the band folding
effect of the stripe structure.Comment: 4 pages, 4 figures, to be published in J. Phys. Soc. Jp
Field Dependence of Electronic Specific Heat in Two-Band Superconductors
The vortex structure is studied in light of MgB theoretically based on a
two-band superconducting model by means of Bogoliubov-de Gennes framework. The
field dependence of the electronic specific heat coefficient is
focused. The exponent in is shown to
become smaller by adjusting the gap ratio of the two gaps on the major and
minor bands. The observed extremely small value could be
explained reasonably well in this two-band model with the gap ratio .Comment: 5 pages, 4 figures, to be published in J. Phys. Soc. Jp
Vortex State and Field-Angle Resolved Specific Heat Oscillation for H // ab in d-Wave Superconductors
When magnetic field is applied parallel to the ab plane in d_{x^2-y^2}-wave
superconductors, the transition of stable vortex lattice structure, spatial
structure of local density of states, and specific heat oscillation by rotation
of magnetic field orientation are investigated by quantitative calculations
based on the selfconsistent Eilenberger theory. We estimate how the vortex
state changes depending on the relative angle between the node-direction of the
superconducting gap and magnetic field orientation. To reproduce the
sign-change of specific heat oscillation observed in CeCoIn_5, our study is
done by including strong paramagnetic effect. The quantitative theoretical
calculations give decisive information to analyze the experimental data on the
field-angle dependence, and establish the angle-resolved specific heat
experiment as a spectroscopic means to identify the node-position of the
superconducting gap.Comment: 9 pages, 13 figure
Site-selective nuclear magnetic relaxation time in a superconducting vortex state
The temperature and field dependences of the site-selective nuclear spin
relaxation time T_1 around vortices are studied comparatively both for s-wave
and d-wave superconductors, based on the microscopic Bogoliubov-de Gennes
theory. Reflecting low energy electronic excitations associated with the vortex
core, the site selective temperature dependences deviate from those of the
zero-field case, and T_1 becomes faster with approaching the vortex core. In
the core region, T_1^{-1} has a new peak below the superconducting transition
temperature T_c. The field dependence of the overall T_1(T) behaviors for
s-wave and d-wave superconductors is investigated and analyzed in terms of the
local density of states. The NMR study by the resonance field dependence may be
a new method to probe the spatial resolved vortex core structure in various
conventional and unconventional superconductors.Comment: 14Pages, 26 figures, revte
Pauli Paramagnetic Effects on Vortices in Superconducting TmNi2B2C
The magnetic field distribution around the vortices in TmNi2B2C in the
paramagnetic phase was studied experimentally as well as theoretically. The
vortex form factor, measured by small-angle neutron scattering, is found to be
field independent up to 0.6 Hc2 followed by a sharp decrease at higher fields.
The data are fitted well by solutions to the Eilenberger equations when
paramagnetic effects due to the exchange interaction with the localized 4f Tm
moments are included. The induced paramagnetic moments around the vortex cores
act to maintain the field contrast probed by the form factor.Comment: 4 pages, 4 figure
Observation of a Triangular to Square Flux Lattice Phase Transition in YBCO
We have used the technique of small-angle neutron scattering to observe
magnetic flux lines directly in an YBCO single crystal at fields higher than
previously reported. For field directions close to perpendicular to the CuO2
planes, we find that the flux lattice structure changes smoothly from a
distorted triangular co-ordination to nearly perfectly square as the magnetic
induction approaches 11 T. The orientation of the square flux lattice is as
expected from recent d-wave theories, but is 45 deg from that recently observed
in LSCO
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