1,721,066 research outputs found
Effects of quasiparticle bound states in the tunneling characteristics of YBa2Cu3O7 readjustable junctions
No full textBy carefully adjusting the distance between the two fractured electrodes, we have investigated the in-plane conductance characteristics of YBa2Cu3O7 break junctions in different tunneling regimes. In the q-p regime we have found that the conductance spectra strongly depend on the misorientation angle between the tunneling current and the YBa2Cu3O7 crystal axis. When the tunneling current along the a-a or b-b axis was favored, conductance maxima and shoulders around +/- 40 and +/- 20 mV have been measured at low temperatures. For different misorientation angles, we have found the presence of a zero bias conductance peak (ZBCP) that develops at the junction T-c as well as gap related structures at about +/- 20 mV. The amplitude of the ZBCP diverges as 1/T for temperatures below 40 K. All these features are consistent with a d-wave model for the high-T-c superconductors
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
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
YBa2Cu3O7-δ/La0.7Ca0.3MnO3 BILAYERS: STRUCTURAL AND TRANSPORT PROPERTIES
No full textWe report on the preparation and the structural characterization of both YBa2Cu3O7-δ/La0.7Ca0.3MnO3 and La0.7Ca0.3MnO3/YBa2Cu3O7-δ bilayers grown onto (100) SrTiO3 substrates. The samples have been realized by sequential dc sputtering processes in high oxygen pressure starting from stoichiometric targets. The X-ray diffractograms and φ-scan reveal a high degree of epitaxiality of the heterostructures. In the case of YBa2Cu3O7-δ topmost layer, we have found a superconducting transition temperature Tc of about 84 K while this is highly depressed when La0.7Ca0.3MnO3 is deposited as outer layer. These last structures recover a higher Tc when a long annealing is carried out at T=560°C
- …
