Studies on the 1/f noise in Shunted Josephson Junctions and Effective Masses in 2DHG GaAs Hall Bars

Abstract

Two projects are presented with the motivation of improving materials and devices for superconducting and semiconducting qubit applications. The first project focuses on quantifying the 1/f noise in SIS Josephson junctions using a dc SQUID. The current-voltage characteristics of two junctions are measured and the degree of thermal rounding is analyzed as a function of temperature. The current-voltage characteristics are then used to compute the voltage bias dependence of both the 1/f and white noise of the junction. Finally, the temperature dependence of the 1/f noise is investigated and found to exhibit a linear relationship within the region of 100mK-4.5K. This is then compared to similar systems in literature. The second project explores a GaAs/AlGaAs 2DHG system using quantum Hall effect measurements. The mobility and charge carrier density dependence is calculated, and an experiment is conducted to investigate their dependence on highly negative top gates. It is discovered that the mobility-density curve increases as the top gate is pushed to more negative values. Furthermore, the spin-orbit interaction is parameterized and compared to previously measured samples. Finally, the band structure of GaAs/AlGaAs holes is discussed in reference to the observed Shubnikov-de Haas oscillations. The effective mass corresponding to the light heavy hole subband is measured using the Ando, Fowler, and Stern equation at low magnetic field oscillations.