42 research outputs found
Magnetization Measurement of a Possible High-Temperature Superconducting State in Amorphous Carbon Doped with Sulfur
Magnetization M(T,H) measurements performed on thoroughly characterized
commercial amorphous carbon powder doped with sulfur (AC-S), revealed the
occurrence of an inhomogeneous superconductivity (SC) below T_c = 38 K. The
constructed magnetic field-temperature (H-T) phase diagram resembles that of
type-II superconductors. However, AC-S demonstrates a number of anomalies. In
particular, we observed (1) a non-monotonic behavior of the lower critical
field H_c1(T); (2) a pronounced positive curvature of the "upper critical field
boundary" that we associated with the flux lattice melting line Hm(T); (3) a
spontaneous ferromagnetic-like magnetization M0 coexisting with SC. Based on
the analysis of experimental results we propose a nonstandard SC state in AC-S.Comment: 18 pages including 5 figure
Penetration of Andreev bound states into the ferromagnet in a SrRuO/(110)YBaCuO bilayer: a scanning tunneling spectroscopy study
Scanning tunneling spectroscopy of thin epitaxial
ferromagnet/superconductor bilayers,
reveal a clear penetration of the Andreev bound states into the ferromagnetic
layer. The penetration is manifested in the density of states of the
ferromagnet as a split zero bias conductance peak with an imbalance between
peak heights. Our data indicate that the splitting occurs at the superconductor
side as a consequence of induced magnetization, confirming recent theoretical
predictions. The imbalance is attributed to the spin polarization in the
ferromagnet.Comment: 4 figure
The internal magnetic field in superconducting ferromagnets
We have measured the nonlinear response to the ac magnetic field in the
superconducting weak ferromagnet Ru-1222, at different regimes of sample
cooling which provides unambiguous evidence of the interplay of the domain
structure and the vorticity in the superconducting state. This is {\em direct}
proof of coexistence of ferromagnetic and superconductive order parameters in
high- ruthenocuprates.Comment: 9 pages, 6 figure
Surface superconducting states in a polycrystalline MgB sample
We report results of dc magnetic and ac linear low-frequency study of a
polycrystalline MgB sample. AC susceptibility measurements at low
frequencies, performed under dc fields parallel to the sample surface, provide
a clear evidence for surface superconducting states in MgB.Comment: 4 pages and 5 figure
Scanning tunneling spectroscopy of SmFeAsO0.85: Possible evidence for d-wave order parameter symmetry
We report a scanning tunneling spectroscopy investigation of polycrystalline
SmFeAsO0.85 having a superconducting transition at 52 K. On large regions of
the sample surface the tunneling spectra exhibited V-shaped gap structures with
no coherence peaks, indicating degraded surface properties. In some regions,
however, the coherence peaks were clearly observed, and the V-shaped gaps could
be fit to the theory of tunneling into a d-wave superconductor, yielding gap
values between 8 to 8.5 meV, corresponding to the ratio 2D/KTc ~ 3.55 - 3.8,
which is slightly above the BCS weak-coupling prediction. In other regions the
spectra exhibited zero-bias conductance peaks, consistent with a d-wave order
parameter symmetry