title: Absorption in the fractional quantum Hall regime: trion dichroism and spin polarization.
abstract: We present measurements of optical interband absorption in the fractional quantum Hall regime in a GaAs quantum well in the range 0<nu<or=1. We investigate the mechanism of singlet trion absorption, and show that its circular dichroism can be used as a probe of the spin polarization of the ground state of the two-dimensional electron system (2DES). We find that at nu<or=1/3 the 2DES is fully spin polarized. Increasing the filling factor results in a gradual depolarization, with a sharp minimum in the dichroism near nu=2/3. We find that in the range 0.5<or=nu<0.85 the 2DES remains partially polarized for the broad range of magnetic fields from 2.75 to 11 T. This is consistent with the presence of a mixture of polarized and depolarized regions.
authors.affiliation: Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot, Israel and Bell Laboratories, Lucent Technology, Murray Hill, New Jersey 07974, USA.
authors.forename: J G
authors.initials: JG
authors.lastname: Groshaus
authors.forename: P
authors.initials: P
authors.lastname: Plochocka-Polack
authors.forename: M
authors.initials: M
authors.lastname: Rappaport
authors.forename: V
authors.initials: V
authors.lastname: Umansky
authors.forename: I
authors.initials: I
authors.lastname: Bar-Joseph
authors.forename: B S
authors.initials: BS
authors.lastname: Dennis
authors.forename: L N
authors.initials: LN
authors.lastname: Pfeiffer
authors.forename: K W
authors.initials: KW
authors.lastname: West
authors.forename: Y
authors.initials: Y
authors.lastname: Gallais
authors.forename: A
authors.initials: A
authors.lastname: Pinczuk