-
[show abstract]
[hide abstract]
ABSTRACT: Optical absorption measurements are used to probe the spin polarization in the integer and fractional quantum Hall effect regimes. The system is fully spin polarized only at filling factor nu=1 and at very low temperatures ( approximately 40 mK). A small change in filling factor (deltanu approximately +/-0.01) leads to a significant depolarization. This suggests that the itinerant quantum Hall ferromagnet at nu=1 is surprisingly fragile against increasing temperature, or against small changes in filling factor.
Physical Review Letters 04/2009; 102(12):126806. · 7.37 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The ground state of the two dimensional electron gas near $\nu$=1 is investigated by inelastic light scattering measurements carried down to very low temperatures. Away from $\nu$=1, the ferromagnetic spin wave collapses and a new low-energy spin wave emerges below the Zeeman gap. The emergent spin wave shows soft behavior as its energy increases with temperature and reaches the Zeeman energy for temperatures above 2 K. The observed softening indicates an instability of the two dimensional electron gas towards a magnetic order that breaks spin rotational symmetry. We discuss our findings in light of the possible existence of a Skyrme crystal. Comment: 4 pages, 4 figures, to appear in Phys. Rev. Lett
09/2007;
-
[show abstract]
[hide abstract]
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.
Physical Review Letters 04/2007; 98(15):156803. · 7.37 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We study the absorption spectrum of a two-dimensional electron gas (2DEG) in a magnetic field. We find that at low temps., when the 2DEG is spin polarized, the absorption spectra, which correspond to the creation of spin up or spin down electrons, differ in magnitude, linewidth, and filling factor dependence. We show that these differences can be explained as resulting from the creation of a Mahan exciton in one case, and of a power law Fermi-edge singularity in the other. [on SciFinder (R)]
Physical Review Letters. 01/2007; 98:186810/1-186810/4.
-
[show abstract]
[hide abstract]
ABSTRACT: Spin excitations from a partially populated composite fermion level are studied above and below nu=1/3. In the range 2/7<nu<2/5, the experiments uncover significant departures from the noninteracting composite fermion picture that demonstrate the increasing impact of interactions as quasiparticle Landau levels are filled. The observed onset of a transition from free to interacting composite fermions could be linked to condensation into the higher order states suggested by transport experiments and numerical evaluations performed in the same filling factor range.
Physical Review Letters 08/2006; 97(3):036804. · 7.37 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We report inelastic light scattering experiments in the fractional quantum Hall regime at filling factors $\nu\lesssim1/3$. A spin mode is observed below the Zeeman energy. The filling factor dependence of the mode energy is consistent with its assignment to spin flip excitations of composite fermions with four attached flux quanta ($\phi$=4). Our findings reveal a composite fermion Landau level structure in the $\phi$=4 sequence. Comment: 7 pages, 4 figures, EP2DS-16 conference, to appear in Physica E
03/2006;
