Institut des
NanoSciences de Paris
insp
Accueil > Evénements > Séminaires > Archives 2014 > « Quantum Phase Transition
insp
6.jpg

« Quantum Phase Transitions in low dimensional disordered films » - Claire Marrache-Kikuchi - Mardi 4 novembre 2014 à 11h

Claire Marrache-Kikuchi - Enseignante-chercheuse au Centre de Sciences Nucléaires et de Sciences de la Matière (CSNSM)

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

Abstract

In disordered systems, the electronic ground state is the result of a competition between Coulomb interactions, disorder, which eventually leads to localization of charge carriers, and, when relevant, superconductivity. In this conflict between antagonistic forces, dimensionality plays a special role and determines what ground states are allowed. Indeed, in three-dimensional systems, two distinct quantum phase transitions, the metal-to-insulator transition (MIT) and the superconductor-to-metal transition, separate the three possible ground states. By contrast, in two dimensions, the system can only exhibit a direct superconductor-to-insulator transition (SIT), since metals are theoretically forbidden in the absence of strong electron-electron interactions. One important question is then to understand how the three ground states (superconducting, metallic, and insulating) that are possible in bulk systems evolve when the thickness is reduced.

The disorder-tuned SIT in thin alloy films provides an interesting way to address this question. I will report on the study of the SIT in NbxSi1-x thin films induced by three different parameters, all related to the amount of disorder in the films : the Nb composition, the thickness and the annealing temperature. Our results show that the effect of the thickness on the destruction of superconductivity is very distinct from those of the composition or the annealing. I will moreover infer the corresponding two-dimensional phase diagram of this system in relation with the three-dimensional one.