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\underline{ELECTRIC FIELD STRUCTURE ON
    THE SURFACE OF SUPERCONDUCTING Pb-In SLAB}
\underline{IN LONGITUDINAL MAGNETIC FIELD}\\
\ \\
\underline{A. Shimogawa}, N. Morita$^{\ast}$, E. S. Otabe, T. Matsushita\\
Department of Computer Science and Electronics, Kyushu
Institute of Technology,\\ 680--4 Kawazu, Iizuka 820,
JAPAN\\

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Since the Lorentz force does not work on the flux lines
under a longitudinal magnetic field, it may be believed that
the energy dissipation is not caused by the motion of the
flux lines under this field. However, in the case of a
cylindrical sample the energy dissipation was theoretically
shown to be caused by the motion of the flux lines driven by
the force-free moment. In order to investigate the mechanism
of energy dissipation the electric field structure on the
surface was measured under a transport current and a
longitudinal magnetic field for superconducting Pb-In slab
samples. An existence of the electric field structure with a
negative electric field region was observed as well as in a
cylindrical sample. It is shown that the electric field
is given by
$\boldmath{E}=\boldmath{B}\times\boldmath{v}-\mbox{grad}\Psi$
where $\boldmath{v}$ and $\Psi$ are the velocity of flux
lines and a scalar function, respectively, and that the negative
electric field originates from the term of
$\boldmath{B}\times\boldmath{v}$. It was found that the
differential resistivity for the current above the critical
one increased with increasing magnetic field similarly to
that in the transverse magnetic field. This result agrees
qualitatively with the interpretation of the Bardeen-Stephen
model under the transverse magnetic field.  As a result it
is concluded that the energy dissipation in slab samples
under the longitudinal field is also caused by the motion of
flux lines.  \\ 

\noindent
present address:
$^{\ast}$Isahaya Electric Corporation,1830--25, Kaizu-cho,
Isahaya, Nagasaki, JAPAN\\\end{document}
















