|
The capability to manipulate electron spins on nanometer length scales, and to control and utilize their dynamic behavior, is one of the most promising
frontiers in nanotechnology. One of the most fascinating possibilities is the prospect that single spins, spin-clusters, and spin-based nanodevice
structures may be model quantum-mechanical systems for understanding the processes of quantum entanglement and quantum decoherence.
The ability to position atoms at surfaces with the STM provides an unprecedented level of control for the fabrication of nanoscale spin systems, creating
the opportunity to systematically examine the foundation science of single-spin and spin-spin interactions. These systems can be built up atom-by-atom and
can be tailored with atomic precision.
Our efforts in this area started with experiments that probed the interactions of a single magnetic atom with a superconductor
[1]. In this situation, the single spin defect introduces a locally bound spin-polarized state in its
immediate vicinity, which can be detected using spectroscopic mapping with the STM. More recently, our interest has turned toward single spin impurities and
their interactions in semiconducting systems, specifically in GaAs. Using the capabilities of our low temperature STM (LTSTM)
we have discovered a method to substitute transition metal atoms, such as Mn, for Ga atoms in GaAs [2,3].
These impurities create highly anisotropic in-gap states associated with the acceptor "hole" in the semiconductor which can be probed directly with the STM.
We are performing a variety of experiments to understand the nature of these unusually shaped electronic states and their interactions with each other.
Pictured below are images of STM topography of a single Mn (left image), a Mn pair separated by 8 Å oriented along <110> (middle image), and a
pair separated by 5.65 Å oriented along <100> (right image). Results show that there is a strong dependence of Mn-Mn interaction on both the
orientation and the spacing. For example, the <110> pair shows a much stronger interaction than the more closely spaced <100> pair. Our work to
assemble a magnetic semiconductor atom by atom, manganese-doped gallium arsenide (Ga1-xMnxAs), and probe its magnetic interactions was recently highlighted
as the cover article in the July 27, 2006 issue of Nature
[3].
|
|
 |
| Image Concept for magnetic interactions of Mn on a GaAs surface. Copyright Ali Yazdani. |
 |
| Gd Atoms on Nd: Topography Image and Spectra Map. Copyright Ali Yazdani. |
|
|
|
 |
 |
 |
| Image of the bound hole state of a single Mn at a Ga site in GaAs. |
Two Mn atoms at 8 Å spacing show a strong ferromagnetic interaction. |
Two Mn atoms at a 5.65 Å spacing do NOT show a ferromagnetic interaction. |
|
- [1] “Probing the Local Effects of Magnetic Impurities on Superconductivity,” Ali Yazdani, B. A. Jones, C. P. Lutz, M. F. Crommie, and D. M. Eigler, Science 275, 1767–1770, (1997). (PDF FORMAT)
- [2] “Spatial Structure of a Single Mn Impurity State on GaAs (110) Surface,” D. Kitchen, A. Richardella, and A. Yazdani, Journal of Superconductivity: Incorporating Novel Magnetism 18, 23 (2005). (LINK)
- [3] “Atom-by-Atom Substitution of Mn in GaAs and Visualization of their Hole-Mediated Interactions,” D. Kitchen, A. Richardella, J.-M. Tang, M. E. Flatté, A. Yazdani, Nature 442, 436 (2006). (PDF FORMAT)
|
