Research

Spin Electronics

Traditional electronics is based on the control with an external electric field (e.g. gate voltage) or quasi-electric field (material composition) of the spatial motion of charged particles (electrons or holes). The physical fact that these charged carriers carry a spin degree of freedom has been largely ignored until recently. In the last few years it has been argued that control of this spin degree of freedom may provide new functionality in electronics, including possible applications in non-volatile memory, reprogrammable logic, or quantum computation.

While focused on the spin degree of freedom, however, it is important to recognize that spin is directly coupled to both to the orbital (spatial) motion of the electrons, and to the self-consistent charge field that they generate as they move through semiconducting materials. Below are links to examples of each of these

• a description of how the spin decoherence in semiconductor materials is determined largely by the coupling between the spin and orbital degrees of freedom An introduction to the method of generating and probing spin packets in semiconductors is provided.

 

• a demonstration of how the space-charge field associated with inhomogeneous spin packets strongly affects their diffusion and mobility properties in semiconductors. Specifically, in spin-polarized semiconductors the diffusion and mobility of spin packets differ by orders of magnitude depending on the relative direction of the packet polarization and the background spin polarization.

Local Coherence in Superconductors

The work on problems of local coherence in superconductors focuses on the effect of impurities and other local inhomogeneities on the electronic structure of the superconductor. These perturbations can be thought of as extremely strong on a local scale, for the potentials associated with atomic impurities are on the order of eV, whereas the energy scale of the superconducting gap is of order meV.

Shown below are results calculated for the dI/dV associated with a resonant state near a Zn atom on the surface of BiSrCaCuO. The four-fold symmetry of the resonant state originates from the underlying square lattice. Such features have been seen with STM measurements by Prof. J. C. Davis at UC Berkeley. The scale is in Angstroms. The horizontal axis is parallel to the Cu-O bonds in the Cu-O planes.

An improved understanding of the effects of impurities on the local electronic structure can assist in understanding the properties of superconducting tunneling devices, as well as loss mechanisms in superconducting mixers. In addition, because these impurities are extremely strong perturbations, their local properties can provide new information about the behavior of the peculiar correlated state corresponding to a high-temperature superconductor.