Measurements of the density-dependent many-body electron mass in two dimensional GaAs/AlGaAs heterostructures

We determine the density-dependent electron mass m({*}) in two-dimensional electron systems of GaAs/AlGaAs heterostructures by performing detailed low-temperature Shubnikov-de Haas measurements. Using very high-quality transistors with tunable electron densities we measure m({*}) in single, high mobility specimens over a wide range of r(s) (6 to 0.8). Toward low densities we observe a rapid increase of m({*}) by as much as 40%. For 2>r(s)>0.8 the mass values fall similar to10% below the band mass of GaAs. Numerical calculations are in qualitative agreement with our data but differ considerably in detail.