Highly disordered superconductors have a rich phase diagram. At a moderate magnetic field (B) the samples go through the superconductor-insulator quantum phase transition. In the insulating phase, the resistance increases sharply with B up to a magne
to-resistance peak beyond which the resistance drops with B. In this manuscript we follow the temperature (T) evolution of this magneto-resistance peak. We show that as T is reduced, the peak appears at lower Bs approaching the critical field of the superconductor-insulator transition. Due to experimental limitations we are unable to determine whether the T=0 limiting position of the peak matches that of the critical field or is at comparable but slightly higher B. We show that, although the peak appears at different B values, its resistance follows an activated T dependence over a large T range with a prefactor that is very similar to the quantum of resistance for cooper-pairs.
It is observed that many thin superconducting films with not too high disorder level (generally R$_N/Box leq 2000 Omega$) placed in magnetic field show an anomalous metallic phase where the resistance is low but still finite as temperature goes to ze
ro. Here we report in weakly disordered amorphous InO$_x$ thin films, that this Bose metal metal phase possesses no cyclotron resonance and hence non-Drude electrodynamics. Its microwave dynamical conductivity shows signatures of remaining short-range superconducting correlations and strong phase fluctuations through the whole anomalous regime. The absence of a finite frequency resonant mode can be associated with a vanishing downstream component of the vortex current parallel to the supercurrent and an emergent particle-hole symmetry of this anomalous metal, which establishes its non-Fermi liquid character.
Highly disordered superconductors, in the magnetic-field-driven insulating state, can show discontinuous current-voltage characteristics. Electron overheating has been shown to give a consistent description of this behavior, but there are other, more
exotic, explanations including a novel, superinsulating state and a many-body localized state. We present AC-DC crossed-measurements, in which the application of a DC voltage is applied along our sample, while a small AC voltage is applied in the transverse direction. We varied the DC voltage and observed a simultaneous discontinuity in both AC and DC currents. We show that the inferred electron-temperature in the transverse measurement matches that in the longitudinal one, strongly supporting electron overheating as the source of observed current-voltage characteristics. Our measurement technique may be applicable as a method of probing electron overheating in many other physical systems, which show discontinuous or non-linear current-voltage characteristics.
Thin films of Amorphous indium oxide undergo a magnetic field driven superconducting to insulator quantum phase transition. In the insulating phase, the current-voltage characteristics show large current discontinuities due to overheating of electron
s. We show that the onset voltage for the discontinuities vanishes as we approach the quantum critical point. As a result the insulating phase becomes unstable with respect to any applied voltage making it, at least experimentally, immeasurable. We emphasize that unlike previous reports of the absence of linear response near quantum phase transitions, in our system, the departure from equilibrium is discontinuous. Because the conditions for these discontinuities are satisfied in most insulators at low temperatures, and due to the decay of all characteristic energy scales near quantum phase transitions, we believe that this instability is general and should occur in various systems while approaching their quantum critical point. Accounting for this instability is crucial for determining the critical behavior of systems near the transition.
