Vibronic spectroscopy using current noise

We demonstrate that there is a strong correlation between the current noise and the inelastic tunneling spectrum of the vibronic current through nanoscale objects. The voltage derivative of the electron-phonon contribution to the noise is found to scale strongly with the contribution to the dynamical conductance when the partition noise vanishes. The scaling relation fails when the partition noise is maximized, i.e., in the case of half transmission, whereas we still find clear vibronic structure in the voltage sweep of the current noise. We have clarified the condition for the scaling relation. The voltage sweep of the current noise can provide us a useful spectroscopy method for the nonequilibrium dynamics of electrons and phonons.