Unusual electronic transport properties of a thin polycrystalline bismuth film

Abstract

The electronic transport properties of a polycrystalline (3420 Å thick)bismuth film have been measured over a wide temperature interval(0.23 K<T<292 K) and a magneticfield range (0 T<B<25 T). The results for the polycrystalline film are very different and anomalous from those ofan epitaxial thin bismuth film. The zero field resistance increases by a factor of five. Themagnetoresistance (MR) values in perpendicular magnetic fields have the same magnitudeat low temperatures as compared to the MR values at room temperature. The Hallcoefficient data in perpendicular fields show oscillations at liquid helium temperatures;there should be no Shubnikov–de Haas oscillations in a polycrystalline bismuth film.The sign of the Hall coefficient at room temperature is positive in small fieldsand becomes negative in large fields. In contrast, the Hall coefficient is alwaysnegative in thick bismuth films. The magnetoresistances in parallel magnetic fieldsshow maxima at intermediate fields followed by decreases at high field values; intheory there should be a small or no MR in the parallel field orientation. The mostanomalous behaviours are large Hall voltages and Hall coefficients in parallelmagnetic fields; the parallel Hall data also have oscillations at low temperatures.The magnetoresistance in transverse fields is anomalous and can be explainedby strong diffused boundary scattering at the top and bottom surfaces of thefilm. Acceptable fits to most of the transport data are obtained using the twocarrier expressions of Pippard and of Fawcett and using the Drude expression.