Temperature as a limitation to the accuracy of SETSAW devices as quantum standards of current

Measurements of the slopes (ΔI/ΔV_g)_n of the acoustoelectric current plateaux I_n=nef for n=1 and 2 have been made, as a function of the bath temperature T in the range 0.3 to 4.2 K. Electrons, constrained in one-dimensional channels, are transported by a surface acoustic wave of frequency f≈2.8 GHz, generated by transducers deposited on a GaAs heterostructure. The channel width is controlled by the application of voltages V_g to Schottky gates also deposited on the heterostructure. The normalised slopes S=(ΔI/ΔV_g)_n/(ΔI/ΔV_g)_n-1→n are compared with those calculated using a model describing the device behaviour proposed by Flensberg et al. (Phys. Rev. B, Condens. Matter, vol. 60, pp. R16291-4, 1999). In this model S is related to an effective temperature T_eff, which can be greater than T. The measurements indicate that for n=1, T_eff has a minimum value of 1.65±0.1 K corresponding to a minimum value of S≈10^-3.