Max Planck Institute of Micostructure Physics
Abstract:
Tunnel junctions are essential for spintronic and superconducting devices for memory and logic applications. We discuss some of our recent work on magnetic tunnel junctions (MTJs) and Josephson junctions (JJs) formed using 2D van der Waals (vdw) materials. In particular, the properties of conventional nano-scale MTJs using ferromagnetic or ferrimagnetic electrodes are dominated by magnetostatic fields that must be eliminated. This is possible using the concept of a synthetic antiferromagnet (SAF). Recently we have demonstrated how a bilayer of the van der Waals antiferromagnetic CrSBr acts just like a SAF in tunnel junctions formed from two “natural” SAFs. Whilst individual CrSBr layers are ferromagnetic with a strong in-plane magnetic anisotropy, these layers are coupled antiferromagnetically so that a bilayer acts just like a SAF. By twisting two bilayers we show that the natural antiferromagnetic coupling between these layers becomes very small, thereby allowing for an all antiferromagnetic tunnel junction that exhibits two non-volatile states in zero magnetic field.
The recent discovery of a Josephson Diode effect (JDE) gives a major impetus to superconducting logic. We have observed a JDE in JJs formed from several 2D van der Waals layer, including NiTe2, PtTe2 and WTe2. An important question is the origin of the JDE and when it is intrinsic and when extrinsic. Vertical Josephson junctions formed from WTe2 show a JDE with a large non-reciprocity in the critical supercurrent when a small magnetic field is applied perpendicular to the supercurrent within the plane of the WTe2 flake. The diode effect strongly depends on the orientation of the magnetic field within the plane of the WTe2 with respect to the crystal structure of the WTe2. These results clearly indicate that the JDE in these devices has an intrinsic origin. JJs with twisted WTe2 layers further support this conclusion. Such an effect could have important applications as a novel magnetic field detector at cryogenic temperatures, for example, to “read” magnetic domain walls in a cryogenic racetrack memory.
Brief CV of Prof. Stuart Parkin:
Stuart Parkin received his B.A. in Physics and Theoretical Physics in 1977 and his Ph.D. in 1980 from the University of Cambridge, UK. His research interests include spintronic materials and devices for advanced sensor, memory, and logic applications, oxide thin-film heterostructures, topological metals, exotic superconductors, and cognitive devices. Parkin is an elected Fellow or Member: Royal Society (London), Royal Academy of Engineering, National Academy of Sciences, National Academy of Engineering, German National Academy of Science-Leopoldina, Royal Society of Edinburgh, Indian Academy of Sciences, and TWAS - academy of sciences for the developing world. Parkin’s awards include the American Physical Society International Prize for New Materials (1994); Europhysics Prize for Outstanding Achievement in Solid State Physics (1997); 2009 IUPAP Magnetism Prize and Neel Medal; 2012 von Hippel Award - Materials Research Society; 2013 Swan Medal-Institute of Physics (London); Alexander von Humboldt Professorship− International Award for Research (2014); Millennium Technology Award (2014); ERC Advanced Grant- SORBET (2015); King Faisal Prize for Science 2021; ERC Advanced Grant – SUPERMINT (2022); 2024 APS Medal for Exceptional Achievement in Research; and 2024 Charles Stark Draper Prize of the National Academy of Engineering. Parkin has received 4 honorary doctorates. Parkin has published >700 papers, has >128 issued patents, and has given >1,000 invited talks around the world. Parkin was named a “Highly Cited Researcher” for the years 2018-2024 and a Citation Laureate™ for 2023 by Clarivate. Parkin has an h-index of 138.
Place: M-236会议室
Host: Xiufeng Han (韩秀峰) / Guoqiang Yu (于国强)
Contact: Qi Fu (傅琦) 82649469