Magnetic field induced emergent inhomogeneity in a superconducting film with weak and homogeneous disorder

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