Dr. Gumbs' area of research and scholarly activities have been dealing with the physics of low-dimensional electron and hole systems, The general thrust of his research work is concerned with developing an understanding of the quantum mechanical properties of the charge carriers in nanoscale semiconductor structures and devices. In particular, current work deals with the exchange and correlation effects on the optical and transport properties of nanostructures. These include Plasmon excitations and electron energy loss spectroscopy for multi-walled and single-walled nanotubes. The effects of magnetic fields and terahertz radiation on the collective excitations of nanotubes.

Other topics of his current research include:

1. The Rashba and Dresselhaus spin-orbit interaction (SOI) effects in quasi-2D and 1D structures including nanotubes. We are examing the role played by SOI on plasma excitations, the ground-state energy and diffusion.

2. Single electron transport using surface acoustic waves (SAWs) in piezoelectric heterostructures and their applications to acoustic spintronics for quantum optics and computing. The quantum entanglement in a SAW nanocircuit and the gate errors associated with leakage are being investigated. [Publication]

3. The photoconductivity at low and intermediate frequencies for the 2D electron system is a subject which is actively being pursued. Plans for extending our technique to the high-frequency regime are being formulated.

4. Low-temperature magnetotransport measurements on GaSb/InAs/AlSb coupled quantum well structures with a GaSb cap layer were recently carried out. We explained the data with self-consistent calculations of their electronic structure. This led to the determination of the surface Fermi level (EFS) of undoped molecular-beam-epitaxy-grown GaSb. We also obtained the dependence of the EFS on the width of the GaSb cap layer. The EFS is pinned around 0.2 eV above the top of the GaSb valence band when the GaSb cap layer width is greater than around 900 Å. For smaller GaSb cap widths, EFS is determined by the surface depletion of holes from the GaSb cap layer. The undoped GaSb/InAs/AlSb heterostructure’s Fermi level is determined by bulk donor defects in the AlSb layer adjacent to the InAs quantum well. Further work is continuing on this project. [Publication]