2,718 research outputs found
Spin Fluctuation Induced Superconductivity Controlled by Orbital Fluctuation
A microscopic Hamiltonian reflecting the correct symmetry of -orbitals is
proposed to discuss superconductivity in heavy fermion systems. In the
orbitally degenerate region in which not only spin fluctuations but also
orbital fluctuations develop considerably, cancellation between spin and
orbital fluctuations destabilizes -wave superconductivity.
Entering the non-degenerate region by increasing the crystalline electric
field, -wave superconductivity mediated by antiferromagnetic
spin fluctuations emerges out of the suppression of orbital fluctuations. We
argue that the present scenario can be applied to recently discovered
superconductors CeTIn (T=Ir, Rh, and Co).Comment: 4 pages, 3 figure
NMR Characterization of Sulphur Substitution Effects in the K(x)Fe(2-y)Se(2-z)S(z) high Tc Superconductor
We present an NMR study of the effect of S substitution in the high Tc
superconductor K(x)Fe(2-y)Se(2-z)S(z) in a temperature range up to 250 K. We
present NMR Knight shift and nuclear spin-lattice relaxation rate 1/T1 data,
and compare our results to that of the non-substituted system K(x)Fe(2-y)Se(2).Comment: Typos fixed, figure replace
Lateral imaging of the superconducting vortex lattice using Doppler-modulated scanning tunneling microscopy
By spatially mapping the Doppler effect of an in-plane magnetic field on the
quasiparticle tunneling spectrum, we have laterally imaged the vortex lattice
in superconducting 2H-NbSe2. Cryomagnetic scanning tunneling spectroscopy was
performed at 300 mK on the ab-surface oriented parallel to the field H.
Conductance images at zero bias show stripe patterns running along H, with the
stripe separation varying as H^-0.5. Regions of higher zero-bias conductance
show lower gap-edge conductance, consistent with spectral redistribution by
spatially-modulated superfluid momentum. Our results are interpreted in terms
of the interaction between vortical and screening currents, and demonstrate a
general method for probing subsurface vortices.Comment: 3 pages, 3 figures, to appear in Applied Physics Letter
Kondo Insulator description of spin state transition in FeSb2
The thermal expansion and heat capacity of FeSb2 at ambient pressure agrees
with a picture of a temperature induced spin state transition within the Fe
t_{2g} multiplet. However, high pressure powder diffraction data show no sign
of a structural phase transition up to 7GPa. A bulk modulus B=84(3)GPa has been
extracted and the temperature dependence of the Gruneisen parameter has been
determined. We discuss here the relevance of a Kondo insulator description for
this material.Comment: Physical Review B in press (2005
77Se NMR Investigation of the K(x)Fe(2-y)Se(2) High Tc Superconductor (Tc=33K)
We report a comprehensive 77Se NMR study of the structural, magnetic, and
superconducting properties of a single crystalline sample of the newly
discovered FeSe-based high temperature superconductor K(x)Fe(2-y)Se(2) (Tc=33K)
in a broad temperature range up to 290 K. We will compare our results with
those reported for FeSe (Tc=9K) and FeAs-based high Tc systems.Comment: Final versio
Strong-coupling theory of superconductivity in a degenerate Hubbard model
In order to discuss superconductivity in orbital degenerate systems, a
microscopic Hamiltonian is introduced. Based on the degenerate model, a
strong-coupling theory of superconductivity is developed within the fluctuation
exchange (FLEX) approximation where spin and orbital fluctuations, spectra of
electron, and superconducting gap function are self-consistently determined.
Applying the FLEX approximation to the orbital degenerate model, it is shown
that the -wave superconducting phase is induced by increasing the
orbital splitting energy which leads to the development and suppression of the
spin and orbital fluctuations, respectively. It is proposed that the orbital
splitting energy is a controlling parameter changing from the paramagnetic to
the antiferromagnetic phase with the -wave superconducting phase
in between.Comment: 4 figures, submitted to PR
Scaling Behavior of Angular Dependent Resistivity in CeCoIn: Possible Evidence for d-Wave Density Waves
In-plane angular dependent resistivity ADR was measured in the non-Fermi
liquid regime of CeCoIn single crystals at temperatures K and in
magnetic fields up to 14 T. Two scaling behaviors were identified in low
field region where resistivity shows T-linear dependence, separated by a
critical angle which is determined by the anisotropy of
CeCoIn; i.e., ADR depends only on the perpendicular (parallel) field
component below (above) . These scaling behaviors and other salient
features of ADR are consistent with d-wave density waves
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