  Negative diagonal magneto-conductivity/resistivity is a spectacular- and
thought provoking- property of driven, far-from-equilibrium, low dimensional
electronic systems. The physical response of this exotic electronic state is
not yet fully understood since it is rarely encountered in experiment. The
microwave-radiation-induced zero-resistance state in the high mobility
GaAs/AlGaAs 2D electron system is believed to be an example where negative
magneto-conductivity/resistivity is responsible for the observed phenomena.
Here, we examine the magneto-transport characteristics of this negative
conductivity/resistivity state in the microwave photo-excited two-dimensional
electron system (2DES) through a numerical solution of the associated boundary
value problem. The results suggest, surprisingly, that a bare negative diagonal
conductivity/resistivity state in the 2DES under photo-excitation should yield
a positive diagonal resistance with a concomitant sign reversal in the Hall
voltage.

Mesoscale and Nanoscale Physics