GHz surface acoustic waves as a probe of composite fermions in two-dimensional electron systems

Abstract

By providing the low-disorder two-dimensional electron system at submicron dimensions, important new length scales are revealed. Using surface acoustic waves of wavelength λ≲1 μm to measure the 2D electron conductivity, enhanced conductivity is observed at even-denominator filling factors v =½, ¼: this represents measurement of composite fermions' conductivity at a dimension smaller than the quasiparticles' mean free path. At smaller λ we are able to observe geometric resonance of the composite fermions' cyclotron orbit and the ultrasound wavelength. Observation of this resonance allows measurement of the composite fermion Fermi wave vector.