title: Inelastic light scattering by gap excitations of fractional quantum hall states at 1/3 </= nu </= 2/3
abstract: We report observations of collective gap excitations of the fractional quantum Hall (FQH) states at filling factors nu = p/(2p+1) ( p = integer), for 1/3</=nu</=2/3, by inelastic light scattering. The collective gap energies at nu = 1/3, 2/5, and 3/7 show a drastic decrease as the value nu = 1/2 is approached. These energies and the one at nu = 3/5 display the linear scaling with (e(2)/epsilonl(0))/|2p+1| that is characteristic of composite fermions in Chern-Simons gauge fields. In a narrow range of nu centered at 1/2, where the FQH gaps collapse, we observe a new excitation mode which exists only at temperatures below 150 mK.
authors.affiliation: Departments of Physics and of Applied Physics, Columbia University, New York, New York 10027 and Bell Labs, Lucent Technologies, Murray Hill, New Jersey 07974, USA.
authors.initials: M
authors.lastname: Kang
authors.initials: A
authors.lastname: Pinczuk
authors.initials: BS
authors.lastname: Dennis
authors.initials: MA
authors.lastname: Eriksson
authors.initials: LN
authors.lastname: Pfeiffer
authors.initials: KW
authors.lastname: West