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

TL;DR

This paper describes a highly stable, ultra-high vacuum scanning tunneling microscope operating at millikelvin temperatures using adiabatic demagnetization refrigeration, enabling long-duration experiments with exceptional temperature control and vibrational isolation.

Contribution

The paper introduces a novel UHV STM system with integrated adiabatic demagnetization refrigeration achieving millikelvin temperatures with high stability and long experimental durations.

Findings

Achieved temperature control between 30 mK and 1 K with 7 μK accuracy.

Demonstrated over 20 hours of stable operation at 50 mK.

Maintained low vibrational noise suitable for atomic-scale measurements.

Abstract

We present the design and performance of an ultra-high vacuum (UHV) scanning tunneling microscope (STM) that uses adiabatic demagnetization of electron magnetic moments for controlling its operating temperature in the range between 30 mK and 1 K with the accuracy of up to 7 $\mu$K. 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 (ADR) can be regenerated automatically within 7 hours 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 through its isolation walls. The 1K pot of the ADR 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 an outstanding mechanical stability, demonstrated by the tunneling current noise, STM imaging, and scanning tunneling spectroscopy measurements all performed on atomically clean Al(100) surface.