Contact shape and the strength of the electron-phonon interaction determined by point contact spectroscopy

The signal in point contact spectroscopy contains information on the absolute strength of the electron-phonon interaction in a metal. In order to determine this strength, however, it is necessary to compare the strength of ohmic and non-ohmic parts of the current and to make some assumption concerning the shape of the contact. In this article we show that the usual assumption of a circular contact would lead to an underestimate of the electron-phonon coupling strength if the actual contact were of more irregular shape. This observation is quantified by explicit calculations for rectangular contacts.