Lorentz Microscopy for Observation of Vortices in Superconductors with “Direction-Free Magnetic Field Application System”

Abstract

Vortices in superconductors (quantized magnetic flux-line) play an important role not only in physical properties but also in practical applications of superconductivity. The small size and weak magnetic flux of vortices, however, have been obstacles to their observation for a long time. Lorentz microscopy with a field emission transmission electron microscope and with a magnetic field application system is indispensable in order to observe individual vortices, and to reveal their structure, configurations and behaviors. In this paper, the Lorentz microscopy and a “direction-free magnetic field application system” dedicatedly developed for a 1-MV field-emission electron microscope are described. This paper also introduces a few observation results in the high-T_c superconductors, Bi₂Sr₂CaCu₂O_8+δ and YBa₂Cu₃O_7-δ.