Regular Article

Robust pseudogap across the magnetic field driven superconductor to insulator-like transition in strongly disordered NbN films^★

¹ Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400005, India
² Department of Physics, National Institute of Technology, Hazratbal, Srinagar, Jammu and Kashmir, India

^a e-mail: indranil.roy@tifr.res.in

Received: 5 August 2018
Received in final form: 7 November 2018
Published online: 4 March 2019

Abstract

We investigate the magnetic field evolution of the superconducting state in a strongly disordered NbN thin film which exhibits a magnetic field tuned superconductor to insulator-like transition, employing low temperature scanning tunneling spectroscopy (STS). Transport measurements of the sample reveals a characteristic magnetic field, which separates the low field state where resistance decreases with decreasing temperature, i.e. dR/dT > 0 and a high-field state where dR/dT < 0. However, STS imaging of the superconducting state reveals a smooth evolution across this field and the presence of a robust pseudogap on both sides of this characteristic field. Our results suggest that the superconductor-insulator transition might be a percolative transition driven by the shrinking of superconducting fraction with magnetic field.