An approach to breaking the 100-milli-Kelvin barrier in electron temperature with a dilution-refrigerator ultrahigh vacuum scanning tunneling microscope.

This study presents a newly constructed dilution-refrigerator ultrahigh vacuum (UHV) scanning tunneling microscope (STM) with a 9/2/2 T superconducting vector magnet capable of achieving electron temperatures as low as 76 mK. Our design emphasizes robust thermal contacts, particularly with the sample holder through a thin insulating layer. Additionally, we focus on effective shielding and grounding against radio-frequency electromagnetic interference by integrating the critical electronics as a physically and electrically integral component of the STM setup. Scanning tunneling spectroscopy results obtained from a superconducting aluminum substrate and a gold tip indicate superior energy resolution, with a higher aspect ratio of the superconducting coherence peak in the dI/dV spectra compared to other dilution-refrigerator UHV STMs. Given that only a handful of UHV STMs with dilution refrigerators have reached electron temperatures below 100 mK, these results demonstrate the effectiveness of our design and methodology in achieving low electron temperatures.