Achieving <i>μ</i>eV tunneling resolution in an <i>in-operando</i> scanning tunneling microscopy, atomic force microscopy, and magnetotransport system for quantum materials research
Johannes Schwenk, S Kim, Julian Berwanger, Fereshte Ghahari, Daniel Walkup, Marlou R. Slot, Son Thanh Le, William Cullen, S. R. Blankenship, Sasa Vranjkovic, Hans J. Hug, Young Kuk, Franz J. Gießibl, Joseph A. Stroscio
Abstract
Research in new quantum materials requires multi-mode measurements spanning length scales, correlations of atomic-scale variables with a macroscopic function, and spectroscopic energy resolution obtainable only at millikelvin temperatures, typically in a dilution refrigerator. In this article, we describe a multi-mode instrument achieving a μeV tunneling resolution with in-operando measurement capabilities of scanning tunneling microscopy, atomic force microscopy, and magnetotransport inside a dilution refrigerator operating at 10 mK. We describe the system in detail including a new scanning probe microscope module design and sample and tip transport systems, along with wiring, radio-frequency filtering, and electronics. Extensive benchmarking measurements were performed using superconductor-insulator-superconductor tunnel junctions, with Josephson tunneling as a noise metering detector. After extensive testing and optimization, we have achieved less than 8 μeV instrument resolving capability for tunneling spectroscopy, which is 5-10 times better than previous instrument reports and comparable to the quantum and thermal limits set by the operating temperature at 10 mK.