Mapping Quantum Fluctuations Near the Superconductor-insulator Transition

The behavior near the superconductor-insulator transition (SIT) is governed by quantum fluctuations. Direct experimental study of such fluctuations is challenging and not easily probed. We use scanning superconductor quantum interference device (SQUID) susceptometer to map the diamagnetic response in a series of TiNbN thin films spanning the SIT. Maps of the diamagnetic response provide information about the local superfluid density. Our measurements reveal electronic superconducting granularity which fluctuates in time and space at temperatures well below Tc. The fluctuations manifest themselves as telegraph-like noise while the temperature regime of these fluctuations grows as the quantum critical point is approached, indicating their quantum nature.