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We report the first direct observation of the cyclotron motion of new quasiparticles in a 2D electron system near y filling factor. Just as electrons in a metal geometrically resonate with a sound wave when a magnetic field is applied perpendicular to the sound propagation direction, near j filling factor we observe resonance of a surface sound wave with cyclotron orbits of charge carriers. The presence of a Fermi surface and geometric resonance of a sound wave with Chern-Simons gauge transformed fermions were explicitly predicted in a recent theory of the half filled Landau level. PACS numbers: 73.20.Dx, 73.40.Kp, 73.50.Jt The two dimensional electron system (2DES) in low disorder GaAs/AlGaAs heterostructures has produced a wealth of experimental results that are changing our understanding of lower dimensional physics. When a large magnetic field is applied to a 2DES containing little disorder, the electron-electron interaction will become manifest at low temperatures. Our understanding of these interactions has been limited largely to what has been gleaned by examining the dominant finding in simple dc transport measurements, the fractional quantum Hall effect (FQHE) [1]. Yet because the interactions are present at more than the odd denominator filling factors of the FQHE, our comprehension of the underlying physics in the electron system is lacking. A picture describing the entire filling factor spectrum is a goal of both theory and experiment. Such a theoretical picture has recently been developed [2], as we outline below. Experimentally it is important to examine the electron-electron interactions throughout the spectrum with a technique that does not destructively perturb the interaction. We have accomplished this and have explored the 2DES in a previously unreachable small length scale regime. In doing so we have revealed a remarkable phenomenon new to the 2DES, and have critically tested this new theory.A useful approach to the problem of the interacting 2D electron system is that of the field theoretic construction. In this method a singular gauge transformation converts the electrons to a system of particles interacting with a "fictitious" or Chern-Simons gauge field. A flux tube containing an integer number n of quanta of Chern-Simons magnetic field is attached to each particle. If n is an odd integer, the transformed particles obey Bose statistics, and if n is even they obey Fermi statistics. In the 2DES the motivation for such a construction is that in a simple Hartree approximation for some choice of n at various rational filling factors the resulting ground state is nondegenerate and as such has a chance of being an approximation to the system's true ground state. While these statistical transmutations have provided a new means of examining the correlated 2DES in an abstract sense, they have not in general presented explicit new properties that are experimentally testable.Recently, however, Halperin, Lee, and Read [2] (HLR) have used the fermion Chern-Simons method to examine the properties of a...

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