Sep 14, 2010
Manipulating spins in magnetic quantum dots
The detection and control of single magnetic atoms in quantum dots represents the fundamental scaling limit for magnetic information storage. The strong and electronically controllable spin-spin interactions that are present in magnetic semiconductors offer an ideal laboratory for exploring the single magnetic spin read-out and control.
In a recent theoretical study published in the journal Nanotechnology, researchers from University of Manitoba, Canada, have investigated electron and hole states in a CdTe quantum dot containing a single magnetic impurity in an external magnetic field. They have shown that the s,p-d spin interaction brings about level anti-crossings between the dark and bright exciton states, and have explained the physics behind these anti-crossings. The results are in good agreement with experimental observations.
The scientists also propose a new magneto-optical mechanism for manipulation of the magnetic impurity spin, which involves using laser pulses and varying the strength of the magnetic field. A simplified picture of the proposed mechanism of impurity spin manipulation in a quantum dot is shown schematically in the image above.
Consider (a) a CdTe quantum dot with a single magnetic impurity (Mn atom with spin S=5/2) in the pure state Sz=–5/2, in an external magnetic field near the anti-crossing point. We can (b) excite the system using a laser pulse to create an exciton in the bright state. The electron and hole thus generated will couple with the impurity due to s,p-d spin interactions. A quick sweep of the magnetic field above the anti-crossing point will generate (c) a spin flip of the magnetic impurity to its value Sz=–3/2. Likewise we can go through all the remaining values of the spin projection of the magnetic atom (Sz=–1/2, 1/2, 3/2 and 5/2).
The properties of quantum dots containing a magnetic impurity, as studied in the article in Nanotechnology, have the potential for applications in the rapidly developing field of quantum information processing, in particular for information storage and read-out.
Additional information can be found in the journal.
About the author
Dr Aram Manaselyan is a postdoctoral fellow in the group of Dr Tapash Chakraborty, professor and Canada Research Chair at the Department of Physics and Astronomy, University of Manitoba, Canada. His work is focused on the theoretical investigation of various nanoscale systems, particularly the electronic and magnetic properties of novel materials that are promising for applications in nanoscale electronics.