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Composite fermions with a valley degree of freedom

The talk explores the physics of the fractional quantum Hall effect in two-dimensional electron systems confined to AlAs quantum wells. In addition to spin, these electrons have a valley degree of freedom which raises the exciting possibility of a transfer of this characteristic to the composite fermions (CFs). We experimentally tune the valley occupation in our system via the application of strain. We perform valley polarization energy measurements for filling factors around nu = 3/2 and find that the CFs act as a single-spin, two-valley system. We repeat these measurements around nu = 1/2 and find qualitative agreement. However, a quantitative comparison betrays particle-hole symmetry breaking. (PhD thesis supervisor: Prof. Mansour Shayegan, Princeton University) Refs: Phys. Rev. Lett. 98, 266404 (2007) Phys. Rev. Lett. 104, 016805 (2010) Phys. Rev. B 81, 113301 (2010)