Issue
EPL
Volume 85, Number 2, January 2009
Article Number 27004
Number of page(s) 5
Section Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties
DOI http://dx.doi.org/10.1209/0295-5075/85/27004
Published online 30 January 2009
EPL, 85 (2009) 27004
DOI: 10.1209/0295-5075/85/27004

Observation of surface superconductivity and direct vortex imaging of a Pb thin island with a scanning tunneling microscope

Y. X. Ning1, C. L. Song1, 2, Z. L. Guan1, X. C. Ma1, Xi Chen2, J. F. Jia2 and Q. K. Xue1, 2

1   Institute of Physics, The Chinese Academy of Sciences - Beijing 100190, China
2   Department of Physics, Tsinghua University - Beijing 100084, China

xcma@aphy.iphy.ac.cn
qkxue@mail.tsinghua.edu.cn

received 7 November 2008; accepted in final form 17 December 2008; published January 2009
published online 30 January 2009

Abstract
We report on a scanning tunneling spectroscopy study on vortex imaging and surface superconductivity of a thin type-II superconducting Pb island, which is epitaxially grown on Si substrate and 12 atomic monolayers in thickness. The field dependence of vortex lattice evolution reveals the existence of the surface superconducting layer, which is parallel to the magnetic field in the periphery of the island and disappears above a critical field $H_{{\rm c}3}$ of 3077 G. The $H_{{\rm c}3}/H_{{\rm c}2}$ ratio of 1.57 gives a further support for the surface superconductivity.

PACS
74.25.Op - Mixed states, critical fields, and surface sheaths.
74.25.Qt - Vortex lattices, flux pinning, flux creep.
68.37.Ef - Scanning tunneling microscopy (including chemistry induced with STM).

© EPLA 2009