Utilizing scanning SQUID microscopy to explore 2D quantum materials

by Prof. Yihua Wang (Fudan University)

Wednesday 24 May 2023, 10:00 → 11:00 Asia/Shanghai

TDLI Meeting Room N600 (East Wing of Floor 6, North Building)

Abstract

Quantum phases such as superconductivity, magnetism and topological orders manifest themselves quite differently in the 2-dimensional (2D) materials than in their bulk counterpart. The famed Berezinskii-Kosterlitz-Thouless (BKT) transition is a prime example: it only occurs in the 2D limit of superconductors and ferromagnets. Experimental methods to study quantum properties of 2D materials are largely based on charge sensing techniques such as electrical transport and tunnelling spectroscopy. Magnetic measurements are just as useful. However, conventional volumetric magnetic probes are not sensitive enough for measuring the weak magnetic signal of 2D materials.

Nano-fabricated superconducting quantum interference devices (nano-SQUID) are very sensitive magnetic probes that are suitable for magnetic imaging of quantum materials on the mesoscopic scale. We have developed scanning SQUID microscopes working under different environments^1,2 to study superconductors, magnets and topological antiferromagnets in the 2D limit. We utilize both magnetometry and susceptometry to image superconducting vortices, magnetization, susceptibility and topological edge current in these systems. In this talk, I will report our recent work on the observations of BKT transition in cuprates³ and of quantum anomalous vortices in iron-based superconductors⁴. If times allows, I will discuss future opportunities at the interface between superconducting nano-devices and quantum materials.

References
1. Pan, Y. P. et al. 3D nano-bridge-based SQUID susceptometers for scanning magnetic imaging of quantum materials. Nanotechnology 30, 305303 (2019). https://doi.org:10.1088/1361-6528/ab1792
2. Xiang, B. K. et al. Flux focusing with a superconducting nano-needle for scanning SQUID susceptometry. arXiv 2209.10748 (2022)
3. Wang, S. Y. et al. Oscillating paramagnetic Meissner effect and Berezinskii-Kosterlitz- Thouless transition in Bi2Sr2CaCu2O8+δ monolayer. arXiv 2112.04782 (2021)
4. Lin, Y. S. et al. Direct Observation of Quantum Anomalous Vortex in Fe(Se,Te). Physical Review X 13, 011046 (2023). https://doi.org:10.1103/PhysRevX.13.011046

Biography

Dr. Yihua Wang is Professor of Physics at Fudan University. He obtained his B.S. from Fudan University in 2005 and Ph.D from Harvard University in 2012, both in Physics. He then became an Urbanek Fellow at Stanford University and returned to Fudan as a faculty in 2015. His research group develops superconducting nano-devices to probe emergent phenomena in quantum materials. He was a recipient of Qiushi Young Investigator award in 2017.

Division

Condensed Matter

Other information

Tencent meeting link: https://meeting.tencent.com/dm/lUBGjKFMiCUs  
Meeting ID: 483 136 148