5,591 research outputs found
Vortex Charging Effect in a Chiral -Wave Superconductor
Quasiparticle states around a single vortex in a -wave
superconductor are studied on the basis of the Bogoliubov-de Gennes (BdG)
theory, where both charge and current screenings are taken into account. Due to
the violation of time reversal symmetry, there are two types of vortices which
are distinguished by their winding orientations relative to the angular
momentum of the chiral Cooper pair. The BdG solution shows that the charges of
the two types of vortices are quite different, reflecting the rotating Cooper
pair of the -wave paring state.Comment: 10 pages, 5 figures, revtex, to be published in Phys. Rev.
The influence of chiral surface states on the London penetration depth in SrRuO
The London penetration depth for the unconventional superconductor
SrRuO is analyzed assuming an order parameter which breaks time
reversal symmetry and parity simultaneously. Such a superconducting state
possesses chiral quasiparticle states with subgap energies at the surface. We
show that these subgap states can give a significant contribution to the
low-temperature behavior of the London penetration depth yielding a
power-law even though bulk quasiparticle spectrum is gapped. The presence of
several electron bands gives rise to interband transition among the subgap
surface states and influences the properties of the surface impedance.
Furthermore, the surface states lead also to a non-linear Meissner effect.Comment: 4 pages, 1 figure, the definition of the Nambu field operator
introduced, and some typos correcte
A polarized neutron-scattering study of the Cooper-pair moment in Sr2RuO4
We report a study of the magnetization density in the mixed state of the
unconventional superconductor S2RuO4. On entering the superconducting state we
find no change in the magnitude or distribution of the induced moment for a
magnetic field of 1 Tesla applied within the RuO2 planes. Our results are
consistent with a spin-triplet Cooper pairing with spins lying in the basal
plane. This is in contrast with similar experiments performed on conventional
and high-Tc superconductors.Comment: Submitted to Physical Review Letter
Role of the exchange and correlation potential into calculating the x-ray absorption spectra of half-metallic alloys: the case of Mn and Cu K-edge XANES in CuMnM (M = Al, Sn, In) Heusler alloys
This work reports a theoretical study of the x-ray absorption near-edge
structure spectra at both the Cu and the Mn K-edge in several CuMnM (M= Al,
Sn and In) Heusler alloys. Our results show that {\it ab-initio} single-channel
multiple-scattering calculations are able of reproducing the experimental
spectra. Moreover, an extensive discussion is presented concerning the role of
the final state potential needed to reproduce the experimental data of these
half-metallic alloys. In particular, the effects of the cluster-size and of the
exchange and correlation potential needed in reproducing all the experimental
XANES features are discussed.Comment: 15 pages, 5 figure
Spinless impurities in high Tc cuprates: Kondo-like behavior
We compare the effects of in-plane non magnetic Li and Zn
impurities on the normal state of high-T cuprates. Y NMR shows that the
extra hole introduced by Li is not localized in its vicinity. The Tc depression
and induced moments on near neighbour Cu sites of Zn or Li are found identical.
These universal effects of spinless impurities establish the major influence of
the spin perturbation with respect to the charge defect. The susceptibility of
the induced moment measured by Li NMR displays a 1/(T+Theta) behavior. Theta
increases with doping up to about 200 K in the overdoped regime. We attribute
this to a "Kondo like" effect.Comment: To appear in Phys.Rev.Lett. (22 nov. 99) Minor modifications compared
to previous version. 8 pages (4 pages for text + 4 figures
Tunnelling spectroscopy of the interface between Sr2RuO4 and a single Ru micro-inclusion in eutectic crystals
The understanding of the zero bias conductance peak (ZBCP) in the tunnelling
spectra of S/N junctions involving d-wave cuprate superconductors has been
important in the determination of the phase structure of the superconducting
order parameter. In this context, the involvement of a p-wave superconductor
such as Sr2RuO4 in tunnelling studies is indeed of great importance. We have
recently succeeded in fabricating devices that enable S/N junctions forming at
interfaces between Sr2RuO4 and Ru micro-inclusions in eutectic crystals to be
investigated.3 We have observed a ZBCP and have interpreted it as due to the
Andreev bound state, commonly seen in unconventional superconductors. Also we
have proposed that the onset of the ZBCP may be used to delineate the phase
boundary for the onset of a time reversal symmetry broken (TRSB) state within
the superconducting state, which does not always coincide with the onset of the
superconducting state. However, these measurements always involved two
interfaces between Sr2RuO4 and Ru. In the present study, we have extended the
previous measurements to obtain a deeper insight into the properties of a
single interface between Sr2RuO4 and Ru.Comment: To appear in J. Phys. Soc. Jpn. Vol. 75 No.12 issu
Superconductivity in Na_xCoO_2yH_2O by charge fluctuation
A new mechanism for superconductivity in the newly discovered Co-based oxide
is proposed by using charge fluctuation. A single-band extended Hubbard model
on the triangular lattice is studied within random phase approximation.
-wave triplet superconductivity is stabilized in the vicinity of
charge-density-wave instability, which is in sharp contrast with the
square-lattice case. The physical origin of the realization of the -wave
triplet state as well as the relevance to experiments are discussed
Superconductivity of Quasi-Two-Dimensional Tight-Binding Electrons in a Strong Magnetic Field
We have investigated the transition temperature of
superconductiv ity in quasi-two-dimensional (Q2D) tight-binding electrons in a
strong magnetic field. When the magnetic field is parallel to 2D conducting
plane, of the Q2D superconductor is shown to increase in an
oscillatory manner as the magnetic field becomes large and to reach in a strong magnetic f ield limit for the spin-triplet superconductor.
We consider the cases of on-site and nearest sites attractive interaction, and
calculate the magnetic field depe ndences of the transition temperature for
various types of symmetry. The first o rder transition from -wave to
-wave is shown to occur at T w hen the magnetic field is
parallel to the direction, which will be observed in a triplet
superconductor, SrRuO.Comment: 13pages,6figure
Spin Nematic Phase in S=1 Triangular Antiferromagnets
Spin nematic order is investigated for a S=1 spin model on triangular lattice
with bilinear-biquadratic interactions. We particularly studied an antiferro
nematic order phase with three-sublattice structure, and magnetic properties
are calculated at zero temperature by means of bosonization. Two types of
bosonic excitations are found. One is a gapless excitation with linear energy
dispersion around , and this leads to a finite spin susceptibility at
T=0 and would have a specific heat at low temperatures. These
behaviors can explain many of characteristic features of recently discovered
spin liquid state in the triangular magnet, NiGa2S4
Upper critical field in layered superconductors
The theoretical statements about a restoration of a superconductivity at
magnetic fields higher than the quasiclassical upper critical field and a
reentrance of superconductivity at temperatures in the
superconductors with open Fermi surfaces are reinvestigated taking into account
a scattering of quasiparticles on the impurities.
The system of integral equations for determination of the upper critical
field parallel to the conducting planes in a layered conventional and
unconventional superconductors with impurities are derived. The
values for the "clean" case in the Ginzburg-Landau regime and at any
temperature in the "dirty" case are found analytically. The upper limit of the
superconductor purity when the upper critical field definately has a finite
value is established.Comment: 10 page
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