42 research outputs found
Tunneling spectroscopy in the magnetic superconductor TmNi2B2C
We present new measurements about the tunneling conductance in the
borocarbide superconductor TmNiBC. The results show a very good
agreement with weak coupling BCS theory, without any lifetime broadening
parameter, over the whole sample surface. We detect no particular change of the
tunneling spectroscopy below 1.5K, when both the antiferromagnetic (AF) phase
and the superconducting order coexist.Comment: Submitted to Phys. Rev. B, Rapid Communication
Anomalous Flux Flow Resistivity in Two Gap Superconductor MgB_2
The flux flow resistivity associated with purely viscous motion of vortices
in high-quality MgB_2 was measured by microwave surface impedance. Flux flow
resistivity exhibits unusual field dependence with strong enhancement at low
field, which is markedly different to conventional s-wave superconductors. A
crossover field which separates two distinct flux flow regimes having different
flux flow resistivity slopes was clearly observed in H//ab-plane. The unusual
H-dependence indicates that two very differently sized superconducting gaps in
MgB_2 manifest in the vortex dynamics and almost equally contribute to energy
dissipation. The carrier scattering rate in two different bands is also
discussed with the present results, compared to heat capacity and thermal
conductivity results.Comment: 4 pages, 3figure
Ginzburg-Landau theory of vortices in a multi-gap superconductor
The Ginzburg-Landau functional for a two-gap superconductor is derived within
the weak-coupling BCS model. The two-gap Ginzburg-Landau theory is, then,
applied to investigate various magnetic properties of MgB2 including an upturn
temperature dependence of the transverse upper critical field and a core
structure of an isolated vortex. Orientation of vortex lattice relative to
crystallographic axes is studied for magnetic fields parallel to the c-axis. A
peculiar 30-degree rotation of the vortex lattice with increasing strength of
an applied field observed by neutron scattering is attributed to the multi-gap
nature of superconductivity in MgB2.Comment: 11 page