Coherent spin transfer in Spin Triplet Superconductor-Magnon Hybrid Structure

Supervisor: Prof. Dr. Stuart Parkin
Responsible Scientist: Dr. Pranava K. Sivakumar

Diagram of a layered superconducting structure with detailed magnification. — Optical microscope image of a vertical spin triplet Josephson junction array coupled to a coplanar waveguide that drives magnons in the permalloy layer.

Optical microscope image of a vertical spin triplet Josephson junction array coupled to a coplanar waveguide that drives magnons in the permalloy layer.

Spin triplet superconductors that carry a spin angular momentum are considered lucrative for the creation of energy efficient spintronic devices^[1]. This phase, though exotic in stoichiometric compounds that can be chemically synthesized, can be readily engineered in superconductor-ferromagnet (SC-FM) heterostructures through the superconducting proximity effect^[2-3]. Multiple works over the past decade have established the existence of equal spin triplet superconductivity in SC/FM/SC Josephson junctions hosting non-collinear spin textures^[4-6]. However, the interaction of the spin angular momentum of the spin triplet superconducting condensate with the underlying or a neighboring magnetic order parameter, which is a crucial aspect for the creation of superconducting spintronic/magnonic devices remains unexplored.

In this project, we fabricate different SC/FM heterostructures and study the evolution of the triplet superconducting order parameter by studying its current-phase relationship, while driving different coherent magnon modes inside the ferromagnet. This is done by measuring the DC and AC Josephson effects in superconducting quantum interference devices (SQUIDs). In addition, this project also explores the nature of spin angular momentum transfer from a spin triplet superconductor to a neighboring ferromagnet. Superconductivity, being a coherent phase of matter is expected to transfer spins more efficiently through specific channels, thereby exciting distinct magnon modes. We will study the nature of these magnons by analyzing the magnonic spectrum generated by triplet supercurrents in a cavity.

Background

Candidates with experience in either one or more of the following topics/skills are preferred:

Josephson junctions
Magnonics
Nanofabrication
RF electronics (Oscilloscope, Spectrum Analyzer, Vector Network Analyzer, Pulse generator, etc.)
Quantum control experiments
LabVIEW programming
Spintronics (MTJs, racetracks)

Literature:

[1]Linder, J. & Robinson, J. W. A. Superconducting spintronics. Nat. Phys. 11, 307-315 (2015)

[2] Bergeret, F. S., Volkov, A. F. & Efetov, K. B. Long-Range Proximity Effects in Superconductor-Ferromagnet Structures. Phys. Rev. Lett. 86, 4096-4099 (2001)

[3] Houzet, M. & Buzdin, A. I. Long range triplet Josephson effect through a ferromagnetic trilayer. Phys. Rev. B 76, 060504 (2007)

[4] Robinson, J. W. A., Witt, J. D. S. & Blamire, M. G. Controlled Injection of Spin-Triplet Supercurrents into a Strong Ferromagnet. Science 329, 59 (2010)

[5] Khaire, T. S., Khasawneh, M. A., Pratt, W. P., Jr. & Birge, N. O. Observation of spin-triplet superconductivity in Co-based Josephson junctions. Phys. Rev. Lett. 104, 137002 (2010).

[6] Jeon, K.-R. et al. Long-range supercurrents through a chiral non-collinear antiferromagnet in lateral Josephson junctions. Nat. Mater. 20, 1358-1363 (2021)

Contact:

For scientific questions about the possible PhD topic, please contact Dr. Pranava K. Sivakumar. For formal questions regarding the application, please contact Michael Strauch.