Condensed Matter Physics Seminar

2 p.m., Thursday, April 22, 2004
Room 1201, Physics Building

 Theory of Insulating Diluted Magnetic Semiconductors

Victor Galitski

(Condensed Matter Theory Center, University of Maryland)

Abstract:  An important recent experimental discovery is that a large number of semiconductors become ferromagnetic when doped carefully with 1-10% of magnetic impurities. Some examples of such "diluted magnetic semiconductors" (DMS) are GaMnAs, GeMn, InMnAs, GaMnN, GaMnP. Ferromagnetic semiconductors, where magnetic and transport properties can be controlled and tuned at will, are projected to form the basic ingredients in the emerging field of spintronics. I will discuss in the talk, the physical mechanisms underlying DMS ferromagnetism within a minimal theoretical model where magnetic coupling between the impurity local moments is mediated by the semiconductor carriers (mostly valence band or impurity band holes). Ferromagnetism occurs irrespective of whether the system is metallic or insulating, leading to a novel percolation theory of DMS ferromagnetism. I will emphasize the effects of disorder in DMS materials which may lead to the appearance of a very unusual Griffiths phase above the ferromagnetic transition point. Such a phase appears due to rare disorder fluctuations, which yield non-perturbative intermittent contributions to various thermodynamic and dynamic response quantities. Within the percolation model, the complicated magnetic phase diagram of DMS systems will be discussed.
Host:  Das Sarma
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