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The Superconducting QUantum Interference Device (SQUID) fabricated on the tip of a sharp quartz pipette (SQUID-on-tip) has emerged as a state-of-the-art tool for nanoscale imaging of magnetic, thermal, and transport properties of advanced quantum devices. In this talk I will give a brief introduction to this technique and present our recent results of its application in graphene and moiré superlattices. These studies demonstrate how nanoscale measurements with exceptionally high sensitivity could improve our understanding of quantum devices.
In the first study, we imaged the de Haas-van Alphen quantum oscillations in a Bernal-stacked trilayer graphene with dual gates, which displays multiple highly tunable bands. We reconstructed the band structure and its evolution with the displacement field with high precision and nanoscale spatial resolution. Furthermore, we unveiled shear-strain-induced pseudomagnetic fields and mapped their spatial dependence. In contrast to artificially induced large strain, which generates pseudomagnetic fields of hundreds of Tesla, we detected naturally occurring pseudomagnetic fields as low as 1 mT corresponding to graphene twisting by 1 millidegree.
In the second study, we measured the quantum oscillations in twisted double-bilayer graphene with flat bands. The quantum oscillations exhibited rich features, revealing the highly tunable band structure. However, they demonstrated significant discrepancies with the single-particle theory. Additionally, we discovered the presence of orbital magnetism in a large phase space, which had not been revealed by transport measurements.
Dr. Haibiao Zhou received his PhD degree in 2015 from the University of Science and Technology of China, under the supervision of Prof. Qingyou Lu. His research focused on the design and construction of a 20 T magnetic force microscope, which he utilized to investigate magnetism and phase separation in corrlated oxides.
Then as a post-doc, he conducted research at the University of St Andrews in Scotland and Seoul National University in South Korea, where he used scanning tunneling microscopy to study superconductors. In 2019, Dr. Zhou joined the group of Prof. Eli Zelodv at the Weizmann Institute of Science, where he has led the development of a mK scanning nanoSQUID microscope and its application in studying quantum devices.
His research findings have been published in journals such as Nature, Nature Communications, and Advanced Materials. Additionally, his contributions to the field of instrumentation have been featured in Review of Scientific Instruments and Ultramicroscopy.
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