Theory of exchange splittings of bands in diluted magnetic semiconductors

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• Prof. Dr. Thomas Dietl, Institute of Physics, Polish Academy of Sciences, and Institute of Physics, University of Warsaw
• Thursday 19 November 2009, 14:15-15:15
• TCM Seminar Room, Cavendish Laboratory.

If you have a question about this talk, please contact Dr Jonathan Keeling.

Giant magneto-optical and magneto-transport effects specific to diluted magnetic semiconductors as well as carrier-mediated ferromagnetism in these systems are known to originate from the presence of a sizable spin-dependent coupling between effective mass carriers and electrons localised on the open d shells of transition metal impurities. A series of recent photoemission and magneto-optical experiments, particularly on magnetically doped nitrides and oxides, but also on (Ga,Mn)As, points to our limiting understanding of the physics governing the sp-d exchange interactions in diluted magnetic semiconductors.

I will present a revisited theory of magneto-optical effects in diluted magnetic semiconductors¹ and show that it explains the unexpected antiferromagnetic sign of the apparent s-d exchange coupling found for photoelectrons in (Ga,Mn)As² and the apparent ferromagnetic p-d exchange interaction reveled by magnetooptical studies for (Zn,Co)O, (Ga,Mn)N, and (Ga,Fe)N³ as well as, a long time ago, for (Ga,Mn)As on the insulator side of the metal-to-insulator transition⁴.

These findings have important consequences on ferromagnetism in these systems and help to understand the evolution of the Curie temperature on going from arsenides to phosphides and to nitrides containing a few percent of randomly distributed Mn ions.

¹ C. Śliwa, T. Dietl, Phys. Rev. B 78, 165205 (2008); T. Dietl, Phys. Rev. B 77, 085208 (2008).

² R. C. Myers et al., Phys. Rev. Lett. 95, 017204 (2005); M. Poggio et al., Phys. Rev. B 72, 235313 (2005); N. P. Stern et al., Phys. Rev. B 75, 045329 (2007).

³ W. Pacuski et al., Phys. Rev. B 73, 035214 (2006); ibid. 76, 165304 (2007); Phys. Rev. Lett. 100, 037204 (2008).

⁴ J. Szczytko et al., Solid State Commun. 99, 927 (1996).

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