Oscillations in the thermal conductivity of a GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As heterostructure in the fractional quantum Hall regime

We report thermal conductivity (TC) experiments on a high-quality GaAs/${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As multiple-quantum-well structure in the fractional quantum Hall regime. We observe magneto-oscillations in TC exhibiting maxima at integral as well as at fractional fillings ν=1/3, 2/3, and 4/3. The results reflect the quasiparticle density of states and demonstrate the absence of gapless excitations in the energy spectrum of the fractional liquid states. At very low temperature, we observe anomalous oscillations in TC which may result from the piezoelectric coupling of the phonons to the two-dimemsional electrons.