Analysis of room-temperature results on normally conducting and superconducting channels through polymer films

Abstract

There are strong reasons from dc and pulsed-current measurements, and from thermal conductivity results, for thinking that narrow channels through films of oxidised atatic polypropylene (OAPP) are superconducting at room temperature. It is thought that the conducting channels, with diameters less than or of the order of a micrometre, are composed of smaller nanofilaments, with diameters of the order of a nanometre. In the present paper a possible explanation is given of measurements which show that the average resistance of non-superconducting channels through films increases with film thickness more slowly than linearly. This result is interpreted in terms of how the Bose condensation temperatures of bosons in arrays of nanofilaments depend on the length and numbers of filaments, and examples are given of parameters of the arrays which could explain the data. The dispersion for the bosons is assumed to consist of a sum of linear and quadratic terms, which is an approximate type of dispersion reported for Cooper pairs. In order to fit the data with the model used, it is necessary to suppose that values of superconducting Tc for channels composed of large numbers of filaments are only slightly above room temperature. It is argued that larger Tc's reported in 1989 when currents of 0.5 A are passed through channels may arise because (a) currents concentrate in a subchannel of smaller width than the original channel, and (b) current-current interactions draw the filaments of the subchannel sufficiently close together to increase the transverse bandwidth and Tc in the model by the required amount.