  When a magnetic field is applied, the mixed state of a conventional Type II
superconductor gets destroyed at the upper critical field Hc2, where the normal
vortex cores overlap with each other. Here, we show that in the presence weak
and homogeneous disorder the destruction of superconductivity with field
follows a different route. Starting with a weakly disordered NbN thin film ( Tc
~ 9K ), we show that under the application of magnetic field the
superconducting state becomes increasingly granular, where lines of vortices
separate the superconducting islands. Consequently, phase fluctuations between
these islands give rise to a field induced pseudogap phase, which has a gap in
the electronic density of states but where the global zero resistance state is
destroyed.
