  In this letter, we analyze a conceptual design for the operation of an Otto
cycle heat machine driven by adiabatic modifications on the electronic
effective mass. Such tailoring of it can be implemented, for instance, via the
application of external electron fields in some materials, as in Gallium
Nitride (GaN). We show that due both the energy quantization on this structure
and the adiabatic transformation of the effective mass, the machine performance
can be improved. The realization of classically inconceivable Otto machines,
with an incompressible working substance, can be realized as well. Our finds
hold in cases where the electronic effective mass, in the low temperature
regime, remains constant during the isochoric strokes.
