The purpose of this investigation is to develop techniques of experimentation in the field of electron transport phenomena.

published_or_final_version / Physics / Doctoral / Doctor of Philosophy

Thesis--Ph. D., University of Hong Kong. / Typewritten.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1962. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 70-73).

The magnetoresistance and Hall coefficient of two single crystals of bismuth have been measured at liquid helium temperatures. The purpose of the work was to investigate the non-linearities which had previously been observed in the longitudinal and Hall voltages as a function of current. In addition to continuous current measurements, a pulsed DC technique was used in an attempt to discriminate between the non-linear effects due to heating and a possible intrinsic current dependence of the magnetoresistance and Hall coefficient. The time dependence of both of these galvanomagnetic effects indicates that the rate of heat dissipation from the crystal into the normal helium increases suddenly about 50 rns after the current is applied. For example, at 4.2 K, 15 kG, and 50 mA, the sample temperature first rises to a value 0.2 K above the bath temperature, and then falls to a steady state value 0.06 K above the bath temperature. The resistance using a continuous current correlates with the steady state value of the time dependent resistance. A possible indication of gravitational dependence of the lambda transition was seen. Both above and below the lambda point the results of the low duty cycle pulsed DC measurements indicate the existence of an intrinsic non-ohmic effect when heating is minimized. The change in the resistance is of the order of I part per thousand per mA. In the normal fluid, the total current dependence of the magnetoresistance and the Hall coefficient is expressible as the sum of the intrinsic current dependence and that due to heating.

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A study of the transport properties of a substance requires the determination of a set of transport coefficients by experiment. From these coefficients, the elements of the electrical conductivity tensor, thermoelectric tensor, et cetera can be determined. In this experiment, measurements and analyses of galvanomagnetic effects in a single crystal of arsenic were performed. The measurements were made at liquid-helium temperatures in magnetic fields ranging to 25 kilogauss. The gross isothermal, electrical conductivities have been analyzed to determine various parameters characterizing the energy bands in arsenic.

The electrical conductivity of InN, group III-V semiconductor, is measured by four point measurement at low temperatures and high magnetic fields. From Resistance Vs temperature measurements (done in the absence of magnetic field) there is a transition from semiconducting state to superconducting state at 2.5K. This superconducting state disappears when the measurements are repeated but at a magnetic field of 0.1 Tesla. Mover the Hall voltage is not proportional to the magnetic field.

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