  Multicontact configuration is one of the most powerful arrangements for
electrical transport measurements applied to study vortex phase transition and
vortex phase dimensionality in strongly anisotropic high-Tc superconducting
materials. In this paper we present electrical transport measurements using a
multiterminal configuration, which prove both the existence of guided vortex
motion in BSCCO single crystals near the transition temperature and that
secondary voltage in zero external magnetic field is induced by thermally
activated vortex loop unbinding. The phase transition between the bound and
unbound states of the vortex loops was found to be below the temperature where
the phase coherence of the superconducting order parameter extends over the
whole volume of the sample. We show experimentally that 3D/2D phase transition
in vortex dimensionality is a length-scale-dependent layer decoupling process
and takes place simultaneously with the 3D/2D phase transition in
superconductivity at the same temperature.
