The superconductor-insulator transition (SIT) is considered an excellent example of a quantum phase transition that is driven by quantum fluctuations at zero temperature. The quantum critical point is characterized by a diverging correlation length and a vanishing energy scale. Low-energy fluctuations near quantum criticality may be experimentally detected by specific heat, c p, measurements. Here we use a unique highly sensitive experiment to measure c p of two-dimensional granular Pb films through the SIT. The specific heat shows the usual jump at the mean field superconducting transition temperature marking the onset of Cooper pairs formation. As the film thickness is tuned towards the SIT, is relatively unchanged, while the magnitude of the jump and low-temperature specific heat increase significantly. This behaviour is taken as the thermodynamic fingerprint of quantum criticality in the vicinity of a quantum phase transition.
Bibliographical noteFunding Information:
We acknowledge support from the Laboratoire dexcellence LANEF in Grenoble (ANR-10-LABX-51-01). A.F. acknowledges support from the EU project MicroKelvin, and by the US-Israel Binational Science Foundation grant no. 2014325. A.A. acknowledges support from the US-Israel Binational Science Foundation grant number 2012233 and from the Israel Science Foundation, grant number 1111/16.
©The Author(s) 2017.