Spin-singlet to triplet Cooper pair converter interface

Matthew Rogers,Sean Langridge,Gavin Burnell,Timothy Moorsom,Rhea Stewart,Machiel G Flokstra,Andrew J Caruana,Fatma Al Ma’Mari,Alistair Walton,Mannan Ali,Harry Bradshaw,Stephen L Lee,Thomas Prokscha,Christian J Kinane,Oscar Cespedes,Bryan J Hickey

doi:10.1038/s42005-021-00567-7

Abstract

Combining magnetic and superconducting functionalities enables lower energy spin transfer and magnetic switching in quantum computing and information storage, owing to the dissipationless nature of quasi-particle mediated supercurrents. Here, we put forward a system where emergent spin-ordering and diffusion of Cooper pairs are achieved at a non-intrinsically magnetic nor superconducting metallo-molecular interface. Electron transport, magnetometry and low-energy muon spin rotation are used to probe time-reversal symmetry breaking in these structures. By comparing the Meissner expulsion in a system including a Cu/C60 spin-converter interface to one without, we observe a paramagnetic contribution that can be explained due to the conversion of spin-singlet Cooper pair states into odd-frequency triplet states. These results demonstrate the potential of metallo-molecular interfaces to achieve singlet to triplet Cooper pair conversion, a capability not present in either metal or molecule separately that could be used in the generation and controlled diffusion of spin polarised dissipationless currents.

Highlights

Combining magnetic and superconducting functionalities enables lower energy spin transfer and magnetic switching in quantum computing and information storage, owing to the dissipationless nature of quasi-particle mediated supercurrents
We study hybrid superconductor/molecule/normal metal (S/M/N) heterostructures using low-temperature electron transport to show that a C60 layer can mediate the leakage of Cooper pair states via the proximity effect
The anomalous response of the sample flux profile in the superconducting state to both temperature and magnetic field provides a compelling case for the presence of unconventional superconducting states present in a hybrid metal/

Summary

Introduction

Combining magnetic and superconducting functionalities enables lower energy spin transfer and magnetic switching in quantum computing and information storage, owing to the dissipationless nature of quasi-particle mediated supercurrents. Odd-frequency superconducting correlations have been probed successfully using transport measurements[10,11], tunnelling spectroscopy[12] and low-energy muon spin rotation (LE-μSR) The latter directly probes the paramagnetic Meissner screening generated by odd-frequency spin-triplet Cooper pairs[13,14,15]. Unlike spin-singlet and SZ = 0 spin-triplet pairs, the equal-spin pairing of the long-range spin-triplet component is no longer subject to pairbreaking mechanisms within ferromagnetic layers These correlations are able to carry dissipationless spin information while facilitating the superconducting proximity of ferromagnets owing to their extended propagation length in spin-polarised materials.

Methods

Results

Conclusion