40 research outputs found
Proximity effect in atomic-scaled hybrid superconductor/ferromagnet structures: crucial role of electron spectra
We study the influence of the configuration of the majority and minority spin
subbands of electron spectra on the properties of atomic-scaled
superconductor-ferromagnet S-F-S and F-S-F hybrid structures. At low
temperatures, the S/F/S junction is either a 0 or junction depending on the
energy shift between S and F materials and the anisotropy of the Fermi
surfaces. We found that the spin switch effect in F/S/F system can be reversed
if the minority spin electron spectra in F metal is of the hole-like type
c-axis penetration depth in BiSrCaCuO single crystals measured by ac-susceptibility and cavity perturbation technique
The -axis penetration depth in
BiSrCaCuO (BSCCO) single crystals as a function of
temperature has been determined using two techniques, namely, measurements of
the ac-susceptibility at a frequency of 100 kHz and the surface impedance at
9.4 GHz. Both techniques yield an almost linear function
in the temperature range T<0.5 T_c.
Electrodynamic analysis of the impedance anisotropy has allowed us to estimate
m in BSCCO crystals overdoped with oxygen
( K) and m at the optimal doping
level ( K).Comment: 5 pages, 4 figure
Giant vortex state in perforated aluminum microsquares
We investigate the nucleation of superconductivity in a uniform perpendicular
magnetic field H in aluminum microsquares containing a few (2 and 4) submicron
holes (antidots). The normal/superconducting phase boundary T_c(H) of these
structures shows a quite different behavior in low and high fields. In the low
magnetic field regime fluxoid quantization around each antidot leads to
oscillations in T_c(H), expected from the specific sample geometry, and
reminiscent of the network behavior. In high magnetic fields, the T_c(H)
boundaries of the perforated and a reference non-perforated microsquare reveal
cusps at the same values of Phi/Phi_0 (where Phi is the applied flux threading
the total square area and Phi_0 is the superconducting flux quantum), while the
background on T_c(H) becomes quasi-linear, indicating that a giant vortex state
is established. The influence of the actual geometries on T_c(H) is analyzed in
the framework of the linearized Ginzburg-Landau theory.Comment: 14 pages, 6 PS figures, RevTex, accepted for publication in Phys.
Rev.
Penetration of Josephson vortices and measurement of the c-axis penetration depth in : Interplay of Josephson coupling, surface barrier and defects
The first penetration field H_{J}(T) of Josephson vortices is measured
through the onset of microwave absorption in the locked state, in slightly
overdoped single crystals (T_{c} ~ 84
K). The magnitude of H_{J}(T) is too large to be accounted for by the first
thermodynamic critical field H_{c1}(T). We discuss the possibility of a
Bean-Livingston barrier, also supported by irreversible behavior upon flux
exit, and the role of defects, which relates H_{J}(T) to the c-axis penetration
depth . The temperature dependence of the latter, determined by
a cavity perturbation technique and a theoretical estimate of the
defect-limited penetration field are used to deduce from H_{J}(T) the absolute
value of .Comment: 9 pages, 6 figure
Surface superconducting states and paramagnetism in mesoscopic superconductors
In the framework of the Ginzburg-Landau equation, the temperature dependence
of the upper critical field of small ring-like superconductors is studied. At
equilibrium small parts of the phase diagram show paramagnetism for width /
radius ratios below 0.85. Their number and extension increase with the size of
the hole. In these regions, only the inner part of the ring shows a positive
magnetic moment. The order parameter density profile appears to change, when
crossing a first order transition line, which separates different angular
momentum values, and we clarify the relationship between the localization of
superconductivity nucleation and paramagnetism of those samples.Comment: 11 pages, 9 figure