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Christoph Strunk - Institute for Experimental and Applied Physics, University of Regensburg, Germany

Evidence for the Charge Berezinskii-Kosterlitz-Thouless transition in insulating TiN films


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Recently a transition from an insulating state with a sheet resistance 1 MOhm to a much more strongly insulating state with an unmeasurably small linear conductance was observed in strongly disordered TiN thin films [1]. It was suggested that this transition may be interpreted as the charge analog of the familiar vortex Berezinskii-Kosterlitz- Thouless (BKT) transition [2], resulting from a granularity within the electronic system [2].

 

We present new data on the linear and non-linear conductance of such films, which allow a separation of competing heating instabilities in the strongly insulating state from the non-linearities typical for the BKT transition. At very low temperatures, we observe power laws I V^ \alpha in the dc IV-characteristics with a strongly temperature dependent exponent \alpha, which is a hallmark of the BKT transition.

 

[1] T. Baturina et al., PRL 99, 257003 (2007).

[2] V. Vinokur et al. Nature 452, 613 (2008).

 

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