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Accueil > Evénements > Séminaires > Archives 2014 > Size-dependent Conduction
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Séminaire propriétés électroniques et opto-électroniques de l’INSP

Size-dependent Conduction as a Probe of Long-Ranged Coulomb Interactions near the Superconductor/Insulator Transition - Christoph Strunk - Mardi 24 juin 2014 à 11 h

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

Mardi 24 juin 2014 à 11 h - INSP - 4 place Jussieu - 75252 PARIS Cedex 05 - Barre 22-32 - 2e étage, salle 201

Abstract

An investigation of the linear and non-linear conduction properties of square TiN films in the insulating regime is presented. A strong dependence on the lateral size L of the films is observed, when L varies between 0.5 and 500mm. This observation invalidates the concept of a local conductivity in our films. At temperatures below 1 K the conductance G(T) is thermally activated and the activation energy Dc grows logarithmically with L. We can relate this size dependence to long-ranged Coulomb interactions, which correspond to anomalously large values of the electrostatic screening length. Between 50mK and 150mK a size dependent saturation of G occurs, and below 50mK the I(V)-curves become non-linear for the largest samples. In the latter case we observe power laws I Va in the dc IV-characteristics with a strongly temperature dependent exponent a, which is a hallmark of the binding of charge/anti-charge pairs in presence of long-ranged interactions. The temperature below which the non-linearities occur agrees well with the independent estimate of the interaction energy extracted from the size dependent activation energy. These observations point towards the importance of long-ranged interactions in our films.