Shot noise in HTc superconductor quantum point contact system

TL;DR

This paper investigates the shot noise and transport properties of a quantum point contact between a lead and high-temperature superconductors with various pairing symmetries, revealing how symmetry affects conductance, noise, and effective charge.

Contribution

It introduces a Hamiltonian and Green function formalism to analyze shot noise in HTc superconductor quantum point contacts with multiple pairing symmetries, including ferropnictides.

Findings

No zero bias conductance peak for $d_{xy}$ symmetry.

Displacement of transport properties in $d+is$ symmetries.

Effective charge varies between $e$ and $2e$, depending on symmetry.

Abstract

We study the electrical transport properties of a quantum point contact between a lead and a Hight Tc superconductor. For this, we use the Hamiltonian approach and non-equilibrium Green functions of the system. The electrical current and the shot noise are calculated with this formalism. We consider $d_{x^2-y^2}$, $d_{xy}$, $d_{x^2-y^2}+is$ and $d_{xy}+is$ symmetries for the pair potential. Also we explore the $s_{+-}$ and $s_{++}$ symmetries describing the behavior of the ferropnictides superconductors. We found that for $d_{xy}$ symmetry there is not a zero bias conductance peak and for $d+is$ symmetries there is a displacement of the transport properties. From shot noise and current, the Fano factor is calculated and we found that it takes values of effective charge between $e$ and $2e$, this is explained by the diffraction of quasiparticles in the contact. For the $s_{+-}$ and $s_{++}$ symmetries the results show that the electrical current and the shot noise depend on the mixing coefficient, furthermore the effective electric charge can take values between 0 and $2e$, in contrast with the results obtained for $s$ wave superconductors.