A millikelvin scanning tunneling microscope in ultra-high vacuum with adiabatic demagnetization refrigeration

We present the design and performance of an ultra-high vacuum scanning tunneling microscope (STM) that uses adiabatic demagnetization of electron magnetic moments for controlling its operating temperature ranging between 30 mK and 1 K with an accuracy of up to 7 mu K rms. At the same time, high magnetic fields of up to 8 T can be applied perpendicular to the sample surface. The time available for STM experiments at 50 mK is longer than 20 h, at 100 mK about 40 h. The single-shot adiabatic demagnetization refrigerator can be regenerated automatically within 7 h while keeping the STM temperature below 5 K. The whole setup is located in a vibrationally isolated, electromagnetically shielded laboratory with no mechanical pumping lines penetrating its isolation walls. The 1 K pot of the adiabatic demagnetization refrigeration cryostat can be operated silently for more than 20 days in a single-shot mode using a custom-built high-capacity cryopump. A high degree of vibrational decoupling together with the use of a specially designed minimalistic STM head provides outstanding mechanical stability, demonstrated by the tunneling current noise, STM imaging, and scanning tunneling spectroscopy measurements, all performed on an atomically clean Al(100) surface. (C) 2021 Author(s).

Automated summary

The ultra-high vacuum scanning tunneling microscope (STM) utilizes adiabatic demagnetization for temperature control to achieve accurate operation at extremely low temperatures, offering long experiment times with high magnetic field capabilities. The setup also features a vibrationally isolated laboratory and a custom-built cryopump for mechanical stability during STM measurements on an Al(100) surface.