1,721,004 research outputs found
Tunneling spectroscopy and surface states in YBa2Cu3O7 and Tl2Ba2CaCu2O8 break junctions
No full textWe present the tunneling characteristics of HTSC break junctions realized on high quality c-axis oriented YBa2Cu3O7 (Y- 123) and TI2Ba2CaCu2O8 (TI-2212) thin films, with T-c (rho = 0) = 91 K and T-c (rho = 0) = 110 K, respectively. By means of this technique, the coupling of the two electrodes can be varied as a function of the externally piloted movements of a micrometric screw. The characteristics are measured in the q-p tunneling regime for different directions. Along the nodal directions. we observe a huge zero bias conductance peak (ZBCP), and gap-related structures at low biases for both materials. For tunneling directions close to (100), the conductance curves show gap-related maxima at about +/- 20 and +/- 40 mV for Y-123 and at about +/- 25 and +/- 50 mV for the TI-2212. In these cases. the ZBCP is highly depressed (5%) or completely absent. (C) 2001 Elsevier Science B.V. All rights reserved
Temperature dependence of gap related structures in YBa2Cu3O7-delta break junctions
No full textWe have applied the break junction technique to highly epitaxial c-axis oriented YBaCuO thin films with T-c(rho =0)=91K deposited on (001) SrTiO3 or LaAlO3 substrates by a high oxygen pressure d.c. sputtering technique. The film thickness was about 1500 Angstrom and a photolithographic process was used to reduce to 100 mum the junction width across the fracture. By this procedure, tunable resistance break junctions with tunneling current favored dong the ab-planes have been realized. The junctions were formed at low temperatures with freshly fractured surfaces and an inert tunnel barrier was created by helium gas or liquid. A good stability was obtained with the normal-state resistance R-N changing about 15% in the temperature range between 4.2 K and 100 K. We have measured the temperature dependence of the conductance maxima that are related to superconducting energy gap at the Fermi level
MgB2: An old material a new superconductor. An extensive scanning tunneling spectroscopy study.
No full textWe have performed an extensive scanning tunneling spectroscopy study on different MgB2 samples. In the standard N–I–S geometry on powders, we observed spectra characterized by pronounced double gap structures that can be modeled by supposing two independent tunneling channels, with gap magnitudes and , i.e., well above and well below the classical BCS limit. In the conductance characteristics of oriented thin films, the presence of the small gap Δπ was predominant and only in few cases a weaker structure appeared around . Recent results on as-grown c-axis oriented single crystals yielded only small gap confirming the 3D π-band nature of this feature, that survives in magnetic field higher than
Detection of the flux dynamical regimes in Bi4O4S3 by multiharmonic AC susceptibility
No full textThe temperature dependent first and third harmonics of the AC magnetic susceptibility χ1,3(T) have been measured on Bi4O4S3. The χ1(T) magnetic response is due to the intergranular contribution with a transition temperature Tc ≈ 4.4 K. The dependencies of the χ3(T) on the AC field amplitude and frequency reveal a critical state with the presence of the flux creep and the flux flow regimes. In fact, the field dependencies of the effective activation energy and of the frequency dependent critical current density have been found to be described with power laws characteristic of the collective creep regime involving large flux bundles
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