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SUMMARY:Quantum Hall ferromagnet at high filling factors:  A magnetic fiel
 d induced Stoner transition - Dr. Benjamin Piot\,  Centre National de la R
 echerche Scientifique\, Grenoble\, France
DTSTART:20070226T141500Z
DTEND:20070226T151500Z
UID:TALK6764@talks.cam.ac.uk
CONTACT:K DAS GUPTA
DESCRIPTION:The integer quantum Hall effect (QHE) observed in the magnetot
 ransport\n properties of a two-dimensional electron gas is usually describ
 ed within\n the framework of a single electron picture. While this picture
  works well\n for the even integer QHE\, this is not the case for the odd 
 integer QHE\,\n where it misses most\, if not all\, of  the essential phys
 ics. Here\, we\n present an experimental investigation of spin splitting i
 n the integer\n quantum Hall effect for a series of AlxGa1-xAs / GaAs hete
 rojunctions and\n quantum wells. Magnetoresistance measurements are perfor
 med at mK\n temperature to characterize the electronic density of states a
 nd estimate\n the strength of many body  interactions. We propose a simple
  model with\n no free parameters which correctly predicts the magnetic fie
 ld required\n to observe spin splitting confirming that the appearance of 
  spin\n splitting is a result of a competition between the disorder induce
 d\n energy cost of flipping spins and the exchange energy gain associated\
 n with the polarized state. In this model\, the single particle Zeeman\n e
 nergy plays no role\, so that the appearance of this quantum Hall\n ferrom
 agnet in the highest occupied Landau level can also be thought of\n as a m
 agnetic field induced Stoner transition.\n
LOCATION:Mott Seminar Room\, Cavendish Laboratory\, Department of Physics
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