Experimental transport studies of yttrium barium copper oxide and lambda-DNA

This dissertation consists of two parts.; In Part I, we focus on the quasi-particle transport properties in the high temperature superconductor YBa₂Cu₃O_7−δ (YBCO), probed by the thermal Hall conductivity (κ _xy). The thermal Hall conductivity selectively reflects the transport behaviors of the charge carriers.; By measuring κ_xy in the normal state YBCO, we established a new method to determine the Wiedemann-Franz (WF) ratio in cuprates. We determined the Hall-channel WF ratio κ _xy/σ_xyT in Cu and YBCO. In the latter, we uncovered a T-linear dependence and suppression of the Hallchannel WF ratio. The suppression of the Hall-channel WF ratio in systems with predominant electron-electron scattering will be discussed.; Thermal transport behaviors of the quasi-particles in the mixed state were studied by measuring κ_xx and κ _xy in a high-purity YBCO crystal. From the field-dependence of the thermal conductivity κ_xx, we separated the quasi particle contribution (κ_e) from the phonon background. In the Hall channel, we observed that the (weak-field) κ _xy increased 103-fold between T _c (90 K) and 30 K, implying a 100-fold enhancement of the quasi-particle lifetime. We found that κ_xy exhibited a specific scaling behavior below ∼30 K. The implication of the scaling behavior will be discussed.; In Part II, we describe an experiment on determining the electrical conductivity of the bacteriophage λ-DNA, an issue currently under intense debate. We covalently bonded the DNA to Au electrodes by incorporating thiol modified dTTP into the ‘sticky’ ends of the λ-DNA. Two-probe measurements on such molecules provided a lower bound for the resistivity ρ > 10 6 μm at bias potentials up to 20 V, in conflict with recent claims of moderate to high conductivity. We stress the importance of eliminating salt residues in these measurements.