The other even-denominator fractions

Experimental data on the sequence of fractional quantum Hall effects (FQHE) states around Landau level filling factor v = 1/2 are well explained withi n the framework of the composite fermion model. Around other even-denominat or fractions the situation is less clear, experimentally as well as theoret ically. In this paper we report experimental studies at even-denominator fi llings at v = 1/4, 3/4, 5/2, etc. We show that the composite fermion pictur e can be applied successfully to the fractions at v = 1/4 and 3/4. Their ef fective mass, when normalized to B-1 (2) (where B is the magnetic field) an d their effective g factor are very similar to the composite fermions at v = 1/2 and 3/2. Our ultra-low-temperature study at v = 5/2 shows that this f raction is a true FQHE state, showing vanishing R-xx and a Hall resistance R-xy precisely quantized to h/(5/2e(2)). (C) 2001 Elsevier Science B.V. All rights reserved.