Princeton Nanoscale Microscopy Laboratory Spintronics at the Atomic-Scale A. Yazdani, Princeton University, DMR-0514522 A novel technique developed by our group uses a scanning tunneling microscope (STM) to substitute magnetic atoms into a semiconductor one atom at a time. This technique has been used to assemble a magnetic semiconductor, manganese-doped gallium arsenide (Ga 1-x Mn x As), atom by atom. Interacting pairs of Mn atoms were studied according to their orientation in the crystal and distance apart. The results of this work were recently highlighted in the cover article of the July 27, 2006 issue of Nature. The effort marks a new degree of control over the atomic-level structure of a semiconductor. Manipulating semiconductors could eventually revolutionize computers by exploiting not just the flow of electrons but also their quantum Mn acceptors in GaAs magnetically interact through the electronic clouds of the acceptor states. The STM is used to assemble pairs of Mn by crystallographic orientation and spacing (five nearest neighbor pairs are shown). The magnetic interaction strength of the above Mn pairs, shown in the graph, depends strongly on