Europhys. Lett.
Volume 62, Number 6, June 2003
Page(s) 883 - 889
Section Condensed matter: electronic structure, electrical, magnetic, and optical properties
Published online 01 June 2003
DOI: 10.1209/epl/i2003-00455-9
Europhys. Lett., 62 (6) , pp. 883-889 (2003)

Scanning tunneling spectroscopy of a-axis $\chem{YBa_2Cu_3O_{7-\delta}}$ films: k-selectivity and the shape of the superconductor gap

A. Sharoni1, G. Leibovitch2, A. Kohen2, R. Beck2, G. Deutscher2, G. Koren3 and O. Millo1

1  Racah Institute of Physics, The Hebrew University - Jerusalem 91904, Israel
2  School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Science, Tel Aviv University - 69978 Tel Aviv, Israel
3  Department of Physics, Technion, Israel Institute of Technology - Haifa 32000, Israel

(Received 21 November 2002; accepted in final form 18 April 2003)

Tunneling spectroscopy of epitaxial (100) oriented $\chem{YBa_2Cu_3O_{7-\delta}}$ films was performed using an STM at 4.2 $\un{K}$. On atomically smooth areas, tunneling spectra revealing clear U-shaped gaps with relatively low zero bias conductance were measured. These spectra can be well fitted to the tunneling theory into a d-wave superconductor only when introducing a strong dependence of the tunneling probability on the wave vector k. Possible origins for this k-selectivity in STM measurements will be discussed. On other areas, V-shaped gaps as well as zero bias conductance peaks are observed, indicating relaxation of k-selectivity and the effect of nanofaceting, respectively.

74.50.+r - Proximity effects, weak links, tunneling phenomena, and Josephson effects.
74.72.Bk - Y-based cuprates.
74.80.-g - Spatially inhomogeneous structures.

© EDP Sciences 2003