Doctoral Defense: Strongly Correlated Multilayer Nanostructures: Longitudinal Charge Transport with Vertex Corrections and Many-Body Effects in Capacitors

Tuesday, July 17, 2012 – 12:00pm
Reiss 262
Simon Hale
Department of Physics

Inhomogeneous dynamical mean-field theory is employed to investigate various interesting multilayer nanoscale systems, including electronic charge transport and capacitance in multilayered nanostructures. The nanostructures are composed of semi-infinite leads that are coupled through a strongly correlated material barrier. The leads are typically metallic, while the barrier region can be tuned from a metal to a Mott insulator by adjusting the particle filling and interaction strength. In addition to the on-site interaction strength and particle filling we can vary other parameters for each individual layer, including the hopping strength, screening length, and chemical potential. Global parameters such as the temperature and barrier thickness can also be adjusted.

The effect of including vertex corrections on the electronic charge transport in the stacking direction is determined. The Falicov-Kimball model is used in transport calculations because there is an exact expression for the vertex corrections. We find this effect to be a relatively small reduction in the resistance-area product when the vertex corrections are included in the calculations of the dc conductivity. As the barrier layer becomes thicker we see saturation in absolute magnitude of this reduction. The reduction in the resistance-area product originates at the interfaces and as the device is made thinner and or more metallic there is a relatively larger effect on the resistance-area product.

We also create a model capacitor. We apply a potential difference at the leads, causing charge to build at the interfaces. By varying the parameters of the barrier and lead layers we can investigate strongly correlated effects on the capacitance. We present two methods for calculating the capacitance: one based on a center-of-charge approach and the other on the voltage profiles through the device. We find the interaction strength has a relatively strong effect on the capacitance of these multilayer nanostructures, while weaker dependence on the temperature and applied potentials.

Research investigating dynamic-field (microwave) assisted magnetic recording is included. Spin trajectories are calculated for large ranges of applied magnetic fields creating Stoner-Wohlfarth like switching asteroids, confirming the reduction in applied field strengths when dynamic fields are present. Additionally, we find an enhancement in the capacitance in nearly depleted systems.