Low-vibration cryostat for AFM-SQUID microscopy

• Subject Area: Condensed Matter Physics
• Term: Funded in 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 563303528

With this proposal, Ludwig-Maximilians-Universität (LMU) München requests to purchase a cryostat to enable AFM-SQUID microscopy to study quantum materials. It is a combination of a superconducting quantum interference device (SQUID) and atomic force microscopy (AFM). The Faculty of Physics at LMU Munich has recently invested in expanding its experimental solid-state physics and sensing programs. Two chairs have been hired (Efetov, Solid State Physics and Allan, Experimental Physics – Quantum Metrology and Sensing) who will work in this area in addition to existing research in theory and experiment. LMU requires new instrumentation for these chairs. The chair for Experimental Physics—Quantum Metrology and Sensing aims to gain an understanding of quantum matter by using the custom instruments that they have built. The goal was always to have the most relevant local information at cryogenic temperatures. This is because a local view often gives unique perspectives, especially in heterogenous materials, and because the most intriguing features of quantum materials can often only be studied at very low temperatures, a few degrees above the absolute zero of the temperature scale. With the AFM-SQUID, LMU will be able to measure highly local electromagnetic phenomena, which cannot be based on instrumentation already existing at LMU. It will be a novel SQUID microscope / SQUID-on-tip system. Similar probes, invented by groups in Stanford, Weizmann, and others, allow to measure local currents, magnetic fields, and dissipation. The resolution varies from tens of nanometers to a micrometer. For the instrument in this Grossgeräteantrag, a new kind of SQUID probe will be used. For Allan’s chair’s research, it is important that the experiments can be done at dilution refrigerator temperatures. To implement these scanning probes, an easy-to-use and easy-to-maintain cryogenic environment that can achieve millikelvin temperatures is needed, with relatively short warm-up/cool-down times so that one can quickly implement changes to the instrument and to the measurement. Finally, vibration levels lower than conventional pulse tube-based cryostats are required for the planned research, which is achieved by having the pulse-tube spatially separated from the probe head. Such a cryostat is currently unavailable at LMU.

• DFG Programme: Major Research Instrumentation
• Major Instrumentation: Kryostat mit geringer Vibration für AFM-SQUID-Mikroskopie
• Instrumentation Group: 8520 Kryostaten, Tauchkühler (bis -100 Grd C)
• Applicant Institution: Ludwig-Maximilians-Universität München
• Leader: Professor Milan Allan