arXiv subjects

C. Attanasio

Publications and source records attributed to C. Attanasio.

23 records · Page 2Linked to original sources

arXiv2009

New aspects of microwave properties of Nb in the mixed state

We present a study of the frequency dependence of the vortex dynamics in a conventional superconductor. We have employed a swept-frequency, Corbino-disk technique to investigate the temperature (3.6K-Tc) and high-field (from Hc2/2 to Hc2) microwave complex resistivity in Nb thin (20-40 nm) films as a function of the frequency (1-20 GHz). We have found several previously unnoticed features: (i) a field-dependent depinning frequency in the GHz range; (ii) deviations from the accepted frequency dependence, that can be ascribed to some kind of vortex creep; (iii) the presence of switching phenomena, reminiscent of vortex instabilities. We discuss the possible origin of the features here reported.

cond-mat.supr-con↗

arXiv2008

Superconducting properties of Nb thin films deposited on porous silicon templates

Porous silicon, obtained by electrochemical etching, has been used as a substrate for the growth of nanoperforated Nb thin films. The films, deposited by UHV magnetron sputtering on the porous Si substrates, inherited their structure made of holes of 5 or 10 nm diameter and of 10 to 40 nm spacing, which provide an artificial pinning structure. The superconducting properties were investigated by transport measurements performed in the presence of magnetic field for different film thickness and substrates with different interpore spacing. Perpendicular upper critical fields measurements present peculiar features such as a change in the H_c2(T) curvature and oscillations in the field dependence of the superconducting resistive transition width at H=1 Tesla. This field value is much higher than typical matching fields in perforated superconductors, as a consequence of the small interpore distance.

cond-mat.supr-con↗

arXiv2004

Interface Transparency of Nb/Pd Layered Systems

We have investigated, in the framework of proximity effect theory, the interface transparency T of superconducting/normal metal layered systems which consist of Nb and high paramagnetic Pd deposited by dc magnetron sputtering. The obtained T value is relatively high, as expected by theoretical arguments. This leads to a large value of the ratio $d_{s}^{cr}/ ξ_{s}$ although Pd does not exhibit any magnetic ordering.

cond-mat.supr-con↗

arXiv2001

Scaling of H_{c2 \perp}(T) in Nb/CuMn Multilayers

Measurements of the perpendicular upper critical magnetic field H_{c2 \perp}(T) are reported for several Nb/CuMn multilayers. It is found that, despite the magnetic nature of the samples, the data for samples with low Mn percentage in the CuMn layers are simply described by the Werthamer-Helfand-Honenberg theory for conventional type-II superconductors, neglecting both Pauli spin paramagnetism and spin orbit impurity scattering. For high Mn concentration a different theoretical aprroach is needed.

cond-mat.supr-con↗

arXiv2000

Irreversibility Line in Nb/CuMn Multilayers with a Regular Array of Antidots

The transport properties of Nb/CuMn multilayers with a regular array of electron beam lithography obtained antidots have been measured at different temperatures in the presence of external perpendicular magnetic fields. Hysteretical I-V characteristics have been observed which disappear when approaching the upper critical magnetic field curve H_{c2}(T). Comparing these data with other results (Arrhenius plots of resistive transition curves, logV-logI characteristics) we have been able to relate the onset of the hysteresis to the presence of an irreversibility line. We discuss several possible mechanisms to clarify the nature of this line. Among them the most plausible seems to be the vortex melting mainly induced by quantum fluctuations.

cond-mat.supr-con↗