Negative conductance in driven Josephson junctions
  We investigate an optimal regime of negative-valued conductance, emerging in a resistively and capacitively shunted Josephson junction, which is driven simultaneously by both, a time-periodic (ac) and a constant (dc) current. We analyze the current-voltage characteristics in the regime of absolute negative conductance. We additionally explore the stability of the negative response with respect to the ac-current frequency. 
Marcin Kostur, Lukasz Machura, Jerzy Luczka, Peter Talkner, Peter   Hanggi