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How free are Composite Fermions at $ν= 1/2$? A NMR investigation

N. Freytag·M. Horvatić·C. Berthier·M. Shayegan·L. P. Lévy
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Abstract

NMR measurements of the electron spin polarization have been performed on a 2D electron system at and around half-filled lowest Landau level. Comparing the magnetic field and the temperature dependence of the spin polarization to models of free and interacting composite fermions (CF), we confirm the existence of a Fermi sea and show that residual interactions are important. Independent measurements of the CF effective mass, g-factor and Fermi energy are obtained from the thermal activation of the spin polarization in tilted fields. The filling factor dependence of the spin polarization for $2/5 < ν< 2/3$ reveals a broken particle-hole symmetry for the partially polarized CF Fermi sea.

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N. Freytag, M. Horvatić, C. Berthier, M. Shayegan, L. P. Lévy. 2002-05-15. How free are Composite Fermions at $ν= 1/2$? A NMR investigation. https://arxiv.org/abs/cond-mat/0205306

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