Specific Heat Measurements through the Superconductor-Insulator Quantum Phase Transition
The superconductor-insulator transition (SIT) is a prototype of a quantum phase transition (QPT) which is very versatile experimentally: varying a non-thermal tuning parameter such as disorder, thickness, composition, magnetic field or gate-voltage causes the system to switch from a superconductor to an insulator at ultra-low temperatures. Though there has been increasing interest in this topic, the SIT has never been addressed from a thermodynamic point of view. So far the experimental study of the SIT has mainly concentrated on dc resistivity based measurements such as transport and magnetoresistance and on global and local tunneling spectroscopy.
In my talk I will describe an experiment designed to go beyond conventional transport measurement. We use a unique highly sensitive setup to measure the specific heat of thin Pb films through the SIT. We find that the specific heat shows the usual jump at the bulk superconducting transition temperature, Tcbulk signaling the superconducting second order phase transition. As the film thickness is tuned toward the SIT, Tc hardly changes, however the magnitude of the jump and low temperature specific heat increase considerably. I will discuss the significance of these results and their contribution to understanding the electronic processes in the vicinity of the QPT.