Shot-Noise in Fractional Wires: a Universal Fano-Factor Different than the Tunneling Charge

Abstract

We consider partially gapped one dimensional (1D) conductors connected to normal leads, as realized in fractional helical wires. At certain electron densities, some distinct charge mode develops a gap due to electron interactions, leading to a fractional conductance. For this state we study the current noise caused by tunneling events inside the wire. We find that the noise's Fano-factor is different from the tunneling charge. This fact arises from charge scattering at the wire-leads interfaces. The resulting noise is, however, universal - it depends only on the identification of the gapped mode, and is insensitive to additional interactions in the wire. We further show that the tunneling charge can be deduced from the finite frequency noise, and yet is interaction dependent due to screening effects.