Unusual electronic transport properties of a thin polycrystalline bismuth film

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