Jason Robinson
Royal Society University Research Fellow
MEng Imperial College London
PhD University of Cambridge
+44 (0)1223 761051
jjr33@cam.ac.uk
people.pwf.cam.ac.uk/jjr33/Home.html
Interaction Between Magnetism and Superconductivity
My research within the Device Materials Group is concerned with investigating the proximity coupling between superconducting and magnetic materials in thin-film multilayers and in heterostructure devices. Due to the weak coupling of these materials, samples are grown with sub-nm thickness control and state-of-the-art nanofabrication techniques are used to create nanoscale superconductor / magnetic devices.
Superconducting Spintronics
Logic processing based on the spin of an electron (spintronics) can be faster than the conventional charge-based equivalent. However, generating and propagating spin currents is not low power because large charge currents are required at device inputs. In the vast majority of superconductors the pairs of electrons which carry charge have antiparallel spins and so supercurrents do not carry a net spin component; by coupling a superconductor with a magnetically inhomogeneous ferromagnet, we recently discovered a way to generate triplet Cooper pairs in which the electrons of a pair have parallel rather than antiparellel spins. A triplet supercurrent therefore carries both charge and spin and could potentially be used in spintronics to create low noise, energy-efficient logic. The aim of this research is first to understand the fundamental properties of this new triplet superconducting state and then to explore the possibility of creating a super-spintronic device.
Josephson Pi Junctions
Supercurrents that flow between superconducting leads through an intervening ferromagnet oscillate as a function of ferromagnetic barrier thickness; consequently, the ground state of such a Josephson device can be 0 or Pi, depending on the barrier thickness. Such devices could potentially be used as low noise phase-shifting elements in superconducting quantum computers. We are investigating a range of junction geometries (nanopillar and planar junctions) with different magnetic barrier materials with the aim of optimizing device performance and also of understanding the interaction of superconducting and magnetic orders. We are also investigating Josephson spin-valves in which the barrier contains multiple magnetic and non-magnetic layers; by manipulating the relative magnetization alignment of the magnetic layers, it is possible both to control the junction phase and to enhance the junction supercurrent.
- JWA Robinson, J Witt & MG Blamire, “Controlled injection of spin-triplet supercurrents into a strong ferromagnet” Science 329, 59 (2010).
- JWA Robinson, G Halász, AI Buzdin & MG Blamire, “Enhanced supercurrents in Josephson junctions containing non-parallel ferromagnetic domains” Phys. Rev. Lett.104, 207001 (2010).
- JWA Robinson, G Halász, MG Blamire, “Crossover induced by spin-density wave interference in the coherence of electron pairs in chromium” Phys. Rev. Lett. 98, 177003 (2009).
- JWA Robinson, S Piano, G Burnell, C Bell & MG Blamire, “Critical current oscillations in strong ferromagnetic Pi junctions” Phys. Rev. Lett. 97, 177003 (2006).