Abstract
The superconductor-insulator transition (SIT) is an excellent example of a quantum phase transition, controlled by a non-thermal tuning parameter g, and dominated by quantum fluctuations, which are expected to be prominent near the quantum critical point. So far, most of the experimental studies of the SIT have focussed on transport properties and tunnelling studies, which do not provide quantitative information on the criticality, and on the physics of the quantum fluctuations close to the transition. In our study, we utilize an experimental tool uniquely suited for the study of the evolution of quantum fluctuations through the quantum critical point: the Nernst effect. Nernst effect, in the past has proved to be a very useful tool in the study of superconducting fluctuations, particularly in the case of phase fluctuations mediated by mobile vortices and antivortices. Such fluctuations are important below the superconducting critical temperature TC, and are responsible for having a finite resistance even at a temperature below TC, at which a finite superconducting amplitude ψ¬0 appears.
In our system of amorphous thin film of Indium Oxide, it is believed that the attainment of zero resistance is mediated by pairing of the mobile vortices and antivortices into immobile dipoles, at a temperature TBKT below TC, the transition being a Berezinskii-Kosterlitz-Thouless (BKT) transition. Using resistivity as our tuning parameter g, we take this system through a disorder-induced SIT, and find significant Nernst signals on both the superconducting and insulating sides of the SIT. Analysis of the Nernst coefficient across the SIT shows remarkable qualitative agreement with a model recently developed for the case of Josephson-coupled superconducting chains [1]. We also obtain, for the first time, the scaling behaviour of the off-diagonal Peltier coefficient αyx, a thermodynamic quantity closely related to the Nernst effect, near a disorder-induced SIT.
References:[1] Y. Atzmon and E. Shimshoni, Phys. Rev. B – Condens. Matter Mater. Phys. 87, 1 (2013).
