Regensburg 2013 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 45: Transport in high magnetic fields / Quantum Hall effect
HL 45.1: Talk
Tuesday, March 12, 2013, 15:00–15:15, H13
Evidence of low-lying gapped excitations in the 5/2 quantum fluid — •Ursula Wurstbauer1,2, Aron Pinczuk1, Ken West3, and Loren Pfeiffer3 — 1Columbia University, New York, USA — 2Walter Schottky Institut and Physik-Department, Technische Universität München, Germany — 3Princeton University, Princeton, USA
The competition between quantum phases that dictate the physics in the second Landau level (SLL) results in striking phenomena. A highly fascinating state is the even denominator fractional quantum Hall (FQHE) state at filling ν=5/2 that is widely believed to support non-Abelian quasi-particle excitations. Our work explores the low-lying neutral excitation modes in the SLL by resonant inelastic light scattering measurements. At 5/2 the spectra revealed a band of gapped modes with peak intensity at energy of 0.07meV. These modes are interpreted as a roton minimum in the wave vector dispersion of spin-conserving excitations. The intensity of the roton band significantly diminishes by increasing the temperature to 250mK and it fully collapses for T>250mK. A long wavelength spin wave mode (SW) is seen at the bare Zeeman energy, indicating non-zero spin-polarization. Both, roton and SW modes appear only in a very narrow filling factor range. A gapless continuum of low-lying excitations emerges at filling factors slightly away from 5/2 demonstrating demonstrates a transition from an incompressible quantum Hall fluid at exactly ν=5/2 to compressible states at very close filling factors. Supported by the U.S. NSF and the AvH.