Recently, Caltech researchers successfully fabricated three, four and five-layer magic Angle torsional graphene devices, and found spin-energy valley symmetry breaking and superconductivity. Stable superconductivity was observed in all three samples, and the superconducting phase gradually occupied a larger portion of the phase diagram space as the number of layers increased, highlighting the role of interactions between flat and dispersive bands in extending the superconducting region in the graphene Mohr superlattice. The research result "Promotion of superconductivity in magic-angle graphene multilayers" was published in Science on September 29, 2022.
Yiran Zhang, the first author of the paper, is a 2018 graduate of Zhiyuan College (the first Zhiyuan Honors Program) majoring in physics. He is currently pursuing his PhD at Caltech. In this research, he was mainly responsible for the preparation of multi-layer magic Angle graphene samples, quantum transport measurement at extremely low temperature and strong magnetic field, data analysis and paper writing. This study is the first time to observe superconductivity in multilayer magic Angle graphene, which greatly expands the strong correlation phenomenon of graphene. The close connection between superconductivity and symmetry breaking phase lays a solid foundation for the experimental and theoretical development of unconventional superconductivity in the future.
In high school, Zhang Yiran was determined to study at a top university. After the college entrance examination, he was admitted to Shanghai Jiao Tong University. With his original intention to study physics, he firmly chose Zhiyuan College. In Zhiyuan's rich scientific research atmosphere, his scientific research seeds began to sprout.
Zhiyuan College encourages undergraduates to conduct scientific researches. In his sophomore year, Zhang Yiran joined the laboratory of Liu Ying and Shi Zhiwen in the School of Physics and Astronomy, SJTU, engaged in two-dimensional materials related research. During his sophomore and junior summers, he joined Professor Nai-Chang Yeh's laboratory at Caltech for summer researches. The training of top laboratories at home and abroad has broadened his scientific research vision, and the patient guidance of scientific research masters has set up a comprehensive view of scientific research for him. "I'm glad I chose Zhiyuan College," said Zhang. "In this environment, everyone is chasing the future they really want, and I can find my true interests."
Zhang Yiran won many honors during his undergraduate study, including Shanghai Outstanding Graduate, Zhiyuan Outstanding Student Scholarship, Kaiyuan Encouragement Scholarship and so on. He graduated from Zhiyuan College with excellent performance and successfully obtained the doctoral offer from California Institute of Technology. During his PhD study, he was mainly engaged in experimental condensed matter physics, focusing on twisting magic Angle graphene and quantum transport measurement of strong correlation and superconductivity in intrinsic graphene. He has achieved stability and improved superconductivity in graphene strongly linked system, and published eight high-level papers in Nature, Science, Nature Physics and other journals, including one with three papers.
Since he had the ambition of becoming a scientist in high school, Zhang Yiran has now entered the scientific research road. He does not feel the hardship of scientific research. On the contrary, he believes that scientific research is a process of discovering interesting matters, and the surprises he finds in the process are even more interesting than the original goals, which is the most attractive part of scientific research.