Absolute negative conductivity in two-dimensional electron systems associated with acoustic scattering stimulated by microwave radiation

We discuss the feasibility of absolute negative conductivity (ANC) in two-dimensional electron systems (2DES's) stimulated by microwave radiation in a transverse magnetic field. The mechanism of ANC under consideration is associated with electron scattering on acoustic phonons accompanied by absorption of microwave photons. It is demonstrated that the dissipative components of the 2DES dc conductivity can be negative (sigma(xx)=sigma(yy)<0) due to negative values of the dc photoconductivity caused by microwave radiation at certain ratios of the microwave frequency Omega and the electron cyclotron frequency Omega(c). The phase of the oscillations of the dissipative dc photoconductivity associated with photon-assisted electron scattering on acoustic phonons is quite different from that in the case of the photon-assisted impurity scattering mechanism. The concept of ANC associated with an interplay of the scattering mechanisms can be invoked to explain the nature of the occurrence of zero-resistance "dissipationless" states observed in recent experiments.