Voltage-induced conformational changes and current control in charge transfer through molecules

Transport through molecular contacts with a sluggish intramolecular vibrational mode strongly coupled to excess charges is studied far from equilibrium. A Born-Oppenheimer approximation in steady state reveals voltage-dependent energy surfaces, which cause abrupt conformational changes of the molecular backbone. These are directly related to transitions between current plateaus, which are relatively robust against thermal fluctuations. In a regime accessible in experiments this allows the operation of a molecular junction as a current switch or as a molecular machine in form of a valve controlled by time-dependent bias and gate voltages.