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Semiconductor electronics has so far been based on the transport of charge carriers while storage of information has mainly relied upon the collective interactions of spins. A new discipline known as spintronics proposes to exploit the strong mutual influence of magnetic and electrical properties in magnetic semiconductors, which promise new types of devices and computer technologies. The mechanism for such phenomena involves the concept of magnetic polarons-microscopic clouds of magnetization composed of charge carriers and neighboring magnetic ions-which determine most of the electrical, magnetic, and optical properties of the material. In spite of the importance of this quasiparticle, its observation remains a formidable challenge. Here we report that, using the positive muon as both a donor center and a local magnetic probe, we have been able to generate and detect the magnetic polaron and determine its size and magnetic moment in the magnetic semiconductor EuS.

The magnetoresistance at temperatures below 20 K in an n-InSb/ In 0.85 Al 0.15 Sb two-dimensional electron system is studied and described in terms of antilocalization due to quantum interference under strong spin-orbit interaction. The spin-orbit interaction coefficients are extracted by fitting the magnetoresistance data to an antilocalization theory distinguishing the Rashba and Dresselhaus contributions. A good agreement between magnetoresistance data and theory suggests a Rashba coefficient ͉␣͉Ϸ0.03 eV Å and a Dresselhaus coefficient ␥ Ϸ 490 eV Å 3 . A strong contribution from the Dresselhaus term leads to pronounced anisotropy in the energy splitting induced by spin-orbit interaction in the two-dimensional electron dispersion.

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