In the case of minibands, this sinusoidal character is no longer preserved. Only high up in the miniband (for wavevectors well beyond 2 π π / d ) is the top actually 'sensed' and does the effective mass change sign. The shape of the miniband dispersion influences miniband transport profoundly and accurate dispersion relation calculations are required given wide minibands. The condition for observing single miniband transport is the absence of interminiband transfer by any process. The thermal quantum k B T should be much smaller than the energy difference E 2 − − E 1 between the first and second miniband, even in the presence of the applied electric field.