Effect of Weak and High Magnetic Fields in Longitudinal and Transverse Configurations on Magneto-Thermoelectric Properties of Quantum Bi wires

摘要

We report on the magneto-thermopower of single-crystal Bi nanowires with diameters 75 nm and 250 nm in a longitudinal and transverse magnetic fields of 0-14T. The temperature range is 1.5-300K. Bi nanowires in a glass capillary have been prepared by the high frequency liquid phase casting. The temperature dependence R(T) shows the transition from metallic to semiconducting behavior due to quantum size effect, where the Bi-wire diameter is reduced to less than 80 nm. It is for the first time that the effect of the negative magneto-resistance in a transverse magnetic field, due to the quantum size effect on 75 nm Bi wires, has been observed. The thermopower is very sensitive to the wire diameter, up to a change in the sign from negative to positive at low temperatures, and to a significant extent in a weak longitudinal magnetic field. The field dependences of longitudinal and transverse magneto-resistance have features characteristic of the occurrence of the quantum size effect and galvanomagnetic size effect, and provide information on the parameters of the energy spectrum and charge carrier mobility. The enhancement of the thermoelectric figure of merit for Bi nanowires is discussed. We also discuss the power factor α~2σ and its dependence on the diameter, magnetic field and temperature.