Carbon nanotube sensor for vibrating molecules

The transport properties of a carbon nanotube (CNT) capacitively coupled to a molecule vibrating along one of its librational modes are studied and its transport properties analyzed in the presence of a scanning tunnel microscope tip. We evaluate the linear charge and thermal conductances of the system and its thermopower. They are dominated by position-dependent Franck-Condon factors, governed by a position-dependent effective coupling constant peaked at the molecule position. Both conductance and thermopower allow us to extract some information on the position of the molecule along the CNT. Crucially, however, thermopower also sheds light on the vibrational level spacing, allowing a more complete characterization of the molecule to be obtained, even in the linear regime.