Point-Contact Spectra of Graphite

Abstract

The current-voltage characteristics of graphite point contacts were measured in the liquid-helium temperature range. The dynamic resistance (dV⁄dI) has a maximum at zero-bias voltage and continuously decreases with increasing bias voltage in contrast to ordinary metal point contacts where dV⁄dI increases with bias voltage. In the second-derivative signal, we observed structures near 17 mV and 56 mV which agree with the peak energies of phonon density of states as determined by neutron inelastic scattering. In small contact-resistance samples, we observed magnetic field dependence of the spectra which is related to the large magnetoresistance of graphite.