Temperature dependence of piezoresistance of composite Fermions with a valley degree of freedom

We report transport measurements of composite Fermions at filling factor ν=3/2 in AlAs quantum wells as a function of strain and temperature. In this system the composite Fermions possess a valley degree of freedom and show piezoresistance qualitatively very similar to electrons. The temperature dependence of the resistance (R) of composite Fermions shows a metallic behavior (dR/dT>0) for small values of valley polarization but turns insulating (dR/dT<0) as they are driven to full valley polarization. The results highlight the importance of discrete degrees of freedom in the transport properties of composite Fermions and the similarity between composite Fermions and electrons.