The first objective of this project on which all the other objective depends is the establishment of the main technique of my lab. The technique is called the SQUID-on-tip (SOT) microscope. These related objectives are essential and technical. In this project, we plan to build one microscope operating at above 4K (1.0) and one operating at 0.1 K (1.2). The 4K microscope was commissioned ahead of schedule and started producing results in January 2020. The 0.1 K microscope was originally scheduled to be operational by the end of the 3rd year of funding. Due to delay in the delivery of the dilution refrigerator, this objective was not fully achieved yet. However, great progress was achieved in the last 6 months and we are confident that the first magnetic images acquired in at ultra-low temperature will be achieved in 2025. Advancement in SOT working at higher temperature than 4.2 K and microwave detection was also not entirely achieved due to unexpected technical difficulties. More work will be needed to complete these objectives.
The second objective is related to unconventional superconductivity. Great progress was achieved in vortex physics. YBCO was the main material mentioned in the proposal. Despite many efforts, we could not get good publishable results in this material. More effort is needed to complete this objective. As an alternative, we explored other promising materials such as Bi2Pd and Nb/EuS heterostructure. In particular, we discovered a new vortex matter phase in Bi2Pd and found the origin of the superconducting diode effect in Nb/EuS bilayer. Other hybrid structures such as chiral molecules deposited on Pb thin films gave good evidence of unconventional superconductivity. Finally, preliminary data suggested surface superconductivity in NbSe2. We demonstrate a device that could braid vortices in such material. That device is a major breakthrough that will be useful in the future to confirm the presence topological superconductivity. Looking into the future, such a device could be part of a topological quantum computer.
The third objective was related to complex oxide heterostructures. In particular LaMnO3/SrTiO3 2D magnetism and LaAlO3/SrTi03 2D superconductivity. Due to the advent of magnetic van der Waals materials, these materials were replaced by other 2D magnetic materials such as CrGeTe3 and CrSBr. These materials were easier to work with and at the forefront of research during the funding period. Major advancement was achieved in that field. The discovery of edge magnetism in CrGeTe3, a new effect that was confirmed in our lab using different techniques. We also investigated antiferromagnetism in CrSBr down to the monolayer, where we measured the magnetic anisotropy and observed magnetic domains in monolayer material. Finally, we also investigated Co2Sn2S3, where we discovered a hidden magnetic texture giving raise to tunable exchange bias. Other groups confirmed this new effect and its origin is now better understood.
All the progress of this proposal is summarized in 11 articles as stated below.
Some of the objectives to enhance the resolution of the technique were met and published in January 2020 in the journal Nanoscale (Objective 1.1 1.2).
Apart from the technical objectives, we also made significant progress in the scientific objectives. Advancements in unconventional superconductivity including hybrid materials and vortex physics (objective 2) were published in a set of four articles published in Physical Review Research in 2020, Advanced Physics Research in 2023, Nature Communications in 2023, and Nano Letters in 2023.
Advancements in 2D magnetism (included in objective 3) were made on two different materials Co2Sn2S3, CrGeTe3, and CrSBr. The work on Co2Sn2S3 was submitted in 2020 and was published in Physical Review B 2022. The work on CrGeTe3 was published in a series of 4 publications Nano Letters in 2022, in ACS Applied Nano Materials in 2023, in Nanoscale in 2024, and in Advanced Science in 2025. Efforts are now being made to disseminate the work on CrGeTe3 in the public media (including social media). Work-related to CrSBr was published in Advanced Materials in 2023.
