Achieving µeV tunneling resolution in an in-operando scanning tunneling microscopy, atomic force microscopy, and magnetotransport system for quantum materials research
Johannes Schwenk, Sungmin Kim, Julian Berwanger, Fereshte Ghahari Kermani, Daniel T. Walkup, Marlou R. Slot, Son T. Le, W. G. Cullen, Steven R. Blankenship, Sasa Vranjkovic, Hans Hug, Young Kuk, Franz Giessibl, Joseph A. Stroscio
Research in new quantum materials require multi-mode measurements spanning length scales, correlations of atomic scale variables with macroscopic function, and with an ultimate energy resolution only obtainable at ultra-low temperatures, typically in a dilution refrigerator. In this article we describe a multi-mode instrument achieving µeV tunneling resolution with in- operando measurement capabilities of scanning tunneling microscopy (STM), atomic force microscopy (AFM), and magnetotransport inside a dilution refrigerator operating at 10 mK. We describe the system in detail including a new scanning probe microscope module design, sample and tip transport systems, along with wiring, radio-frequency (RF) filtering, and electronics. Extensive benchmarking measurements were performed using superconductor-insulator- superconductor (SIS) tunnel junctions, with Josephson tunneling at zero bias a noise metering detector. After extensive testing and optimization, we demonstrate we can achieve less than 8 µeV tunneling resolution, which is approximately 5-10 times better than previous instrument reports and comparable to the quantum and thermal limits set by the operating temperature at 10 mK.