Strong odd-frequency correlations in fully gapped Zeeman-split superconductors

TL;DR

This paper demonstrates that odd-frequency superconducting correlations can exist even with a fully gapped density of states in Zeeman-split superconductors, challenging previous assumptions and proposing experimental detection methods.

Contribution

It provides a theoretical framework showing odd-frequency pairing can occur without DoS signatures and suggests a new experimental approach for detection.

Findings

Odd-frequency pairing can exist with a fully gapped DoS.

Derived a generalized criterion for odd-frequency effects on DoS.

Proposed an experiment to detect odd-frequency pairing via magnetic field application.

Abstract

It is now well established that at a superconductor/ferromagnet (S/F) interface an unconventional superconducting state arises in which the pairing state is odd-frequency. The hallmark signature of this superconducting state is generally understood to be an enhancement of the electronic density of states (DoS) at subgap energies close to the S/F interface. However, here we show that an odd frequency state can be present even if the DoS is fully gapped. As an example, we show that this is the case in the pioneering S/FI (where FI is a insulating ferromagnet) tunneling experiments of Meservey and Tedrow, and we derive a generalized analytical criterium to describe the effect of odd-frequency pairing on the DoS. Finally, we propose a simple experiment in which odd-frequency pairing in a Zeeman-split superconductor can be unambiguously detected via the application of an external magnetic field.