Intergrain Connectivity and Resistive Broadening in Vortex State: A Comparison Between ${\rm MgB}_{2}$, ${\rm NbSe}_{2}$ and ${\rm Bi}_{2}{\rm Sr}_{2}{\rm Ca}_{2}{\rm Cu}_{3}{\rm O}_{10}$ Superconductors

Magnetoresistance and radio frequency penetration depth techniques are used to study grain connectivity and broadening of the superconducting transition. We study these issues in three different superconducting systems e.g. MgB
₂
, NbSe
₂
and Bi
₂
Sr
₂
Ca
₂
Cu
₃
O
₁₀
. Some of the samples are irradiated with heavy ions. From the rf response, the bulk pinning force constant is evaluated. From high field transport measurements,
H
-
T
phase diagrams are compared for the three systems with varying degrees of fluctuation and connectivity.