SEARCH FOR NAGAOKA FERROMAGNETISM
IN DOPED SEMICONDUCTORS WITHOUT MAGNETIC IONS
Department of Electrical Engineering and
Ferromagnetism is believed to occur in several “single-band” models of electronic systems with a low density of mobile carriers – from the electron gas, to Hubbard models near half filling in the large U limit. In real electronic materials, effects of disorder often come into play at low carrier densities, limiting the applicability of such models. Thus, for example, ferromagnetism has not been seen in semiconductors with shallow, non-magnetic dopants at any density, despite the full freedom to tune the ratio of the electron kinetic energy and e-e interaction.
In this talk, we exploit the result that the addition of a second band allows the system to achieve ferromagnetism, in diluted magnetic semiconductors, to re-examine the semiconductor system doped with nonmagnetic ions. In particular, we show that the maximum likelihood of obtaining Nagaoka ferromagnetism is in a region which is inaccessible to bulk systems. In this regime, which can be studied in semiconductor quantum dots as well as heterostructures, we demonstrate the existence of high (and maximal) spin ground states at the nanoscale, and speculate on the possibility of ferromagnetism at larger length scales. Possible experimental signatures will be discussed.