Magnetoresistance of amorphous indium oxide films on the insulating side near the superconductor-insulator transition

Abstract

The magnetoresistance (MR) of amorphous indium oxide films on the insulating side near the superconductor-insulator transition was measured. Variable range hopping is evident in the presence of a high enough magnetic field even in the temperature range where simple activation prevails in the absence of a magnetic field, which strongly suggests the existence of localized superconducting granules. Consequently, junction breaking between superconducting granules and pair breaking effects dominate the MR at low enough temperatures. As those effects caused by the local superconductivity on MR decrease rapidly with increasing temperature, an intrastate interaction effect becomes significant. The observed MR is fitted to a theoretical expression which includes junction breaking, pair breaking and intrastate interaction terms. The temperature dependence of the fitting parameters shows qualitative agreement with theoretical expectations.

Anomalous parallel-field negative magnetoresistance in ultrathin films near the superconductor-insulator transition

“…This was first observed in In 2 O 3 films some years ago by a Bell Laboratories group [20], and has been reported more recently by groups in Russia, Korea, Israel, and the US, respectively [21][22][23][24][25]. One might argue that the data shown here is actually the same physics, but that the magnetic field scale is dramatically reduced because the films are close to criticality with regard to disorder.…”

“…Another set of potentially relevant experiments are the studies of the SI transition in perpendicular magnetic fields, where a peak, followed by negative MR is found at fields larger than the critical field of the SI transition. This was first observed in In 2 O 3 films some years ago by a Bell Laboratories group [20], and has been reported more recently by groups in Russia, Korea, Israel, and the US, respectively [21][22][23][24][25]. One might argue that the data shown here is actually the same physics, but that the magnetic field scale is dramatically reduced because the films are close to criticality with regard to disorder.…”

Superconductivity of very thin films: The superconductor–insulator transition

“…They suggested this was a signature of a transition or crossover between Bose and Fermi insulators and that the order parameter amplitude was non-vanishing in the insulating regime. More recently there have been a number of papers confirming and extending this work [54,102,103,104,105,106]. An alternative to the Bose-to-Fermi insulator crossover at this field is that the insulating regime consists of intermixed superconducting and normal phases.…”

Thickness dependence of superconductivity and superconductor–insulator transition in ultrathin FeSe films on SrTiO 3 (001) substrate

“…For the fractal Pb thin films on Si(111), the NMR with wide magnetoresistance terrace under perpendicular magnetic field was reported and attributed to the coexistence of two superconducting phases in this factual film [36]. In the case of granular Pb films and amorphous indium oxide thin films, a large NMR was observed on the insulating side of 2D superconductor-insulator transition and attributed to the dominance of intergranular tunneling and the Cooper pair breaking effects, respectively [34,35]. A distinct feature in our case is that the NMR only occurs in the vicinity of superconducting transition under a relatively weak magnetic field and is correlated well with the upturn behavior shown in figure 4(a).…”