Coherent Spin Transfer in Spin Triplet Superconductor-Ferromagnet Hybrid Structures

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.

Your goals

Fabrication and characterization of spin triplet Josephson junctions
Demonstration of dynamic effects of magnons on spin triplet supercurrents
Demonstration of spin angular momentum transfer through spin triplet supercurrents
Understand the nature of quantum spin transfer through experiments and theoretical models.

Your profile

We are seeking a highly motivated candidate with

An MSc degree in physics, materials science or related fields including a final thesis project.
Demonstrated track record of excellence in research and coursework.

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.)
LabVIEW programming
Spintronics (MTJs, racetracks)

Why join us?

This fully funded PhD position provides the opportunity to work in a dynamic research environment equipped with state-of-the-art nanofabrication and cryogenic measurement facilities under the supervision of Prof. Dr. Stuart S. P. Parkin in the NISE (Nano-systems from Ions, Spins and Electrons) department at MPI Halle. The project offers significant scope for high-impact research at the forefront of condensed matter physics and nanotechnology.

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.

References:

[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)