Excess photon-assisted noise of Majorana and Andreev bound states

Abstract

Photon-assisted tunneling arises under an ac bias, with the drive frequency setting the photon energy. The excess photon-assisted noise is defined as the difference between the shot noise under a combined dc and ac bias and that under a dc bias alone. We investigate this quantity in tunneling into the Majorana or Andreev bound states, which are of great interest in the search for topological superconductors. Under a harmonic bias V(t)=Vdc[1−cos(Ωt)], the excess photon-assisted noise exhibits distinct behaviors: for Majorana or quasi-Majorana bound states, it undergoes multiple sign reversals as Vdc increases and vanishes at nonzero integer values of eVdc/Ω (with e the elementary charge), whereas for zero-energy Andreev bound states—particularly those producing nearly quantized zero-bias conductance peaks—it remains strictly negative over the entire Vdc range.

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