Study of Nucleation and Annihilation of Antiparallel Fluxoids in Superconductors

1994 Fiscal Year Final Research Report Summary

• Project/Area Number: 05640421
• Research Category: Grant-in-Aid for General Scientific Research (C)
• Allocation Type: Single-year Grants
• Research Field: 固体物性Ⅱ(磁性・金属・低温)
• Research Institution: KYUSHU UNIVERSITY
• Principal Investigator: AOMINE Takafumi Kyushu University Department of Physics Professor, 理学部, 教授 (50037206)
• Project Period (FY): 1993 – 1994
• Keywords: Antiparallel fluxoids / Fluxoid motion

Research Abstract

Electrical currents flow at conducting leads which are located at both sides of granular Al thin film with thichness thiner than the coherence length. The electrical current through the conducting lead gives one dimensional magnetic field to the abovethin film. Using the magnetic field which takes zero and changesits polarity in the sample, we showed previously that nucleation and annilation of antiparallel fluxoids are possible.
The purpose of this study is to estimate the value oflambda。 introduced to protect divergence in the formula of average magnetic field over the sample width and to use conducting leads prepared by photolithographic technique. In case of Cu films as the conducting leads, Joule heat raised sample temperature and it was difficult to keep the sample temperature constant. Then we used Nb thin films, which are superconducting and do not generate Joule heat, as the conducting leads.
We measured the voltage V due to fluxoid motion as functions of transport current I and the current i which produces the magnetic field with spatial gradients. The measured results showed a linear relation between V vs. I or V vs. i only near a critical temperature To but showed a nonlinear relation between them at low temperatures. The calculated results show only linear relation. Therefore we can compare the measured resuts near Tc with the calculated ones.
The obtained value oflambda。 was of order of the 10mum and depended on I.The latter result was not obtained by calculation. In any way we are waiting for the calculation which shows the nonlinear relation between V and I,or V and i at low temperatures.