37 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
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
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
The low-frequency response in the surface superconducting state of ZrB single crystal}
The large nonlinear response of a single crystal ZrB to an ac field
(frequency 40 - 2500 Hz) for has been observed. Direct
measurements of the ac wave form and the exact numerical solution of the
Ginzburg-Landau equations, as well as phenomenological relaxation equation,
permit the study of the surface superconducting states dynamics. It is shown,
that the low frequency response is defined by transitions between the
metastable superconducting states under the action of an ac field. The
relaxation rate which determines such transitions dynamics, is found.Comment: 7 pages, 11 figure
Annama H chondrite-Mineralogy, physical properties, cosmic ray exposure, and parent body history
The fall of the Annama meteorite occurred early morning (local time) on April 19, 2014 on the Kola Peninsula (Russia). Based on mineralogy and physical properties, Annama is a typical H chondrite. It has a high Ar-Ar age of 4.4 Ga. Its cosmic ray exposure history is atypical as it is not part of the large group of H chondrites with a prominent 7-8 Ma peak in the exposure age histograms. Instead, its exposure age is within uncertainty of a smaller peak at 30 +/- 4 Ma. The results from short-lived radionuclides are compatible with an atmospheric pre-entry radius of 30-40 cm. However, based on noble gas and cosmogenic radionuclide data, Annama must have been part of a larger body (radius >65 cm) for a large part of its cosmic ray exposure history. The Be-10 concentration indicates a recent (3-5 Ma) breakup which may be responsible for the Annama parent body size reduction to 30-35 cm pre-entry radius.Peer reviewe
Tunneling spectroscopy measurement of the superconductor gap parameter of MgB_2
Cryogenic scanning tunneling microscopy and magnetization measurements were
used to study the superconducting properties of MgB_2. The magnetization
measurements show a sharp superconductor transition onset at T_c = 38.5 K, in
agreement with previous works. The tunneling spectra exhibit BCS gap
structures, with gap parameters in the range of 5 to 7 meV, yielding a ratio of
2delat/KT_c ~ 3-4. This suggests that MgB_2 is a conventional BCS (s-wave)
superconductor, either in the weak-coupling or in the `intermediate-coupling`
regimeComment: accepted to PRB, revised versio