Archana Mishra

Measurement of magnetic penetration depth and superconducting energy gap in very thin epitaxial NbN films

We investigate evolution of the magnetic penetration depth and superconducting energy gap in epitaxial NbN films using a low frequency mutual inductance technique and tunneling spectroscopy using a low temperature scanning tunneling microscope (STM). The superconducting transition temperature (Tc) for films grown under optimal growth conditions decreases monotonically from 15.87K to 9.16K as the film thickness is decreased from 50nm to 3nm. With decrease in film thickness delta(0) monotonically decreases, whereas lambda(0) monotonically increases. We observe that Tc, lambda(o) and delta(0) are well described by Bardeen-Cooper-Schrieffer (BCS) theory in all films other than the two thinnest ones where we see evidence of the Kosterlitz-Thouless-Berezinski (KTB) transition close to Tc.

Tunneling studies in a homogeneously disordered s-wave superconductor: NbN

We report the evolution of superconducting properties as a function of disorder in epitaxial NbN thin films grown on 100 MgO substrates. The effective disorder in these films encompasses a large range, with kFl 1.38‐8.77. Tunneling measurements reveal that for films with large disorder the superconducting transition temperature is not associated with a vanishing of the superconducting energy gap but with a large broadening of the superconducting density of states. Our results provide strong evidence of the loss of superconductivity via phase fluctuations in a homogeneously disordered s-wave superconductor.

Temperature dependence of resistivity and Hall coefficient in strongly disordered NbN thin films

We report the temperature dependence of resistivity

Topological transitions in a model with particle-hole symmetry, Pancharatnam-Berry curvature, and Dirac points

(\ensuremath{\rho})

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and Hall coefficient

Effects of interaction in the Hofstadter regime of the honeycomb lattice

({R}_{H})

Effect of phase fluctuations on the superconducting properties of strongly disordered 3D NbN thin films

in the normal state of homogeneously disordered epitaxial NbN thin films with

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{k}_{F}l\ensuremath{\sim}1.68\char21{}10.12

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. The superconducting transition temperature

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({T}_{c})