Large Josephson current in Weyl nodal loop semimetals due to odd-frequency superconductivity

TL;DR

This paper demonstrates that Weyl nodal loop semimetals can host exceptionally large Josephson currents due to the emergence of odd-frequency superconductivity, making them promising for superconducting applications.

Contribution

It reveals that WNLs can support large Josephson currents through odd-frequency pairing, a novel mechanism enabled by their unique electronic structure.

Findings

WNLs exhibit large Josephson currents due to odd-frequency pairing.

Spin-triplet pairing is induced from spin-singlet pairs via Weyl dispersion.

WNL Josephson junctions can be used to detect odd-frequency superconductivity.

Abstract

Weyl nodal loop semimetals (WNLs) host a closed nodal line loop Fermi surface in the bulk, protected zero-energy flat band, or drumhead, surface states, and strong spin-polarization. The large density of states of the drumhead states makes WNL semimetals exceedingly prone to electronic ordering. At the same time, the spin-polarization naively prevents conventional superconductivity due to its spin-singlet nature. Here we show the complete opposite: WNLs are extremely promising materials for superconducting Josephson junctions, entirely due to odd-frequency superconductivity. By sandwiching a WNL between two conventional superconductors we theoretically demonstrate the presence of very large Josephson currents, even up to orders of magnitude larger than for normal metals. The large currents are generated both by an efficient transformation of spin-singlet pairs into odd-frequency spin-triplet pairing by the Weyl dispersion and the drumhead states ensuring exceptionally proximity effect. As a result, WNL Josephson junctions offer unique possibilities for detecting and exploring odd-frequency superconductivity.