Non-universal scaling of rho(xx) peak widths of gated GaAs/AlGaAs in the IQHE regime

A systematic study of the halfwidths of the rho(xx) peaks, Delta B(T), and (partial derivative rho(xy)/partial derivative B)(max) as a function of electron density, or equivalently disorder, has been undertaken. Our samples are lon mobility, gated GaAs/Al0.3Ga0.7As heterostructures (HS). Scaling arguments predict the linewidths of rho(xx) peaks in the IQHE to vary as Delta B-T-kappa, where kappa is universal. We find that kappa decreases with increasing Landau level number, is a function of disorder and is sample dependent. We investigate peaks 0 down arrow, 1 up arrow, 1 down arrow and unsplit peaks 1-4 at densities in the range 2-6 x 10(11) cm(-2) For the 1 up arrow peak, kappa is 0.6 at high densities. Values of kappa range from 0.15 to 0.4 for unsplit peaks These results differ from reported kappa = 0.42 for InGaAs/InP HS and some GaAs/AlGaAs HS below 200 mK.