Suppression of weak localization effects in low-density metallic 2D holes

We have measured the conductivity in a gated high-mobility GaAs two dimensional hole sample with densities in the range (7-17)x10^9 cm^-2 and at hole temperatures down to 5x10^-3 E_F. We measure the weak localization corrections to the conductivity g=G/(e^2/h) as a function of magnetic field (Delta g=0.019 +/- 0.006 at g=1.5 and T=9 mK) and temperature (d ln g/dT<0.0058 and 0.0084 at g=1.56 and 2.8). These values are less than a few percent of the value 1/pi predicted by standard weak localization theory for a disordered 2D Fermi liquid