Composite Fermions with Spin at $ν=1/2$
Proceedings- International School of Physics Enrico Fermi
© Societa Italiana di Fisica
The model of Composite Fermions for describing interacting electrons in two dimensions in the presence of a magnetic field is described. In this model, charged Fermions are combined with an even number of magnetic flux quanta in such a way that the external magnetic field is compensated on the average for half filling of Landau levels and the interaction is incorporated into an effective mass of the new composite particles. The fluctuations of the Chern-Simons gauge field, which describes formally the flux attachment, induce new interactions between the Composite Fermions. The effective interaction is investigated with particular emphasis on the role of the electron spin at filling factor $\nu=1/2$. For a system with equal numbers of spin-up and spin-down electrons it is found that the dominant effective interaction is attractive in the spin-singlet channel. This can induce a ground state consisting of Cooper pairs of Composite Fermions that is separated from the excited states by a gap. The results are used to understand recent spin polarization measurements done in the region of the Fractional Quantum Hall Effect at different constant filling factors.
Acknowledgment This work has been supported by the European Union via the TMR and RTN programmes (FMRX-CT98-0180, HPRN-CT2000-00144), by the Deutsche Forschungsgemeinschaft within the Schwerpunkt “Quanten-Hall-Effekt” of the Universit¨at Hamburg, and by the Italian MURST via PRIN00.
to be published in proceedings of Varenna Summer School "E. Fermi": Course CLI "Quantum phenomena in mesoscopic systems", July 2002
This is the author accepted manuscript. The final version is available from IOS press via the DOI in this record.
B. Kramer, E. Mariani, N. Magnoli, M. Merlo, F. Napoli, M. Sassetti, (2003) in Composite Fermions with spin at ν = 1/2, pp. 395-415 in Proceedings of the International School of Physics "Enrico Fermi"; Volume 151: Quantum Phenomena in Mesoscopic Systems.