Nanopattern-stimulated superconductor-insulator transition in thin TiN films

Abstract

We present the results of the comparative study of the influence of disorder on transport properties in continuous and nanoperforated TiN films. We show that nanopatterning turns a thin TiN film into an array of superconducting weak links and stimulates both, the disorder-and magnetic field-driven superconductor-to-insulator transitions, pushing them to lower degree of disorder. We find that nanopatterning enhances the role of the two-dimensional Coulomb interaction in the system transforming the originally insulating film into a more pronounced insulator. We observe magnetoresistance oscillations reflecting collective behaviour of the multiconnected nanopatterned superconducting film in the wide range of temperatures and uncover the physical mechanism of these oscillations as phase slips in superconducting weak link network.That a thin film of the same material can be a superconductor but can very well turn an insulator, is one of the most remarkable aspects of disordered superconductors [1][2][3][4][5][6][7]. The engine driving the transition between the superconducting and insulating states is disorder the effect of which is two-fold. On the one hand, disorder limits the electron diffusion enhancing thus the Coulomb electron-electron interaction which competes with the Cooper pairing [8,9]. The latter in an interplay with the disorder-induced inhomogeneities localizes Cooper pairs to form an insulating state, Cooper-pair insulator. A restricted geometry is critical to effects of disorder -for the insulating state to be observed the superconducting material is to be thinned down till its thickness d becomes comparable to or smaller than the superconducting coherence length ξ. One of the major experimental challenges in these studies remains the optimization of material parameters taking it to the closest proximity of the direct superconductor-insulator transition and identifying the systems that exhibit such a transition at available temperatures. In this Letter we meet this challenge via creating a metamaterial with the desirable properties, the multiconnected thin superconducting film. We show that nanopatterning a thin TiN film into a regular sievelike configuration turns it into an array of weak links and, therefore, stimulates the direct superconductor-toinsulator transition. Depending on the original degree of disorder it either suppresses the critical temperature T c , or drives the initially superconducting film into an insulating state, or else, transforms the originally insulating film into an even more pronounced insulator.As a starting material we have chosen a 5 nm thin TiN film which was identical by its parameters to those that experienced the superconductor-insulator transition after soft plasma etching [10][11][12][13] and which were fully characterized by the high resolution electron beam, infrared [14], and low-temperature scanning tunnelling spectroscopy [15]. The smooth, continuous, and uniform TiN film was formed on the Si/SiO 2 substrate by atomic layer deposition. The film had the super...

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“…In particular, the zero-temperature phase can be tuned to a conductor [3] and an insulator [5] by making the distance between grains larger than the coherence length. The increased level of control over the spatial complexity and disorder in a regular square array of nanostructured superconductors has made Nicola Poccia nicola.poccia@utwente.nl nicola.poccia@nano.cnr.it 1 MESA+ Institute for Nanotechnology, University of Twente, P.O.…”

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