A 30 mK, 13.5 T scanning tunneling microscope with two independent tips

Abstract

We describe the design, construction, and performance of an ultra-low temperature, high-field scanning tunneling microscope (STM) with two independent tips. The STM is mounted on a dilution refrigerator and operates at a base temperature of 30 mK with magnetic fields of up to 13.5 T. We focus on the design of the two-tip STM head, as well as the sample transfer mechanism, which allows \textit{in situ} transfer from an ultra high vacuum (UHV) preparation chamber while the STM is at 1.5 K. Other design details such as the vibration isolation and rf-filtered wiring are also described. Their effectiveness is demonstrated via spectral current noise characteristics and the root mean square roughness of atomic resolution images. The high-field capability is shown by the magnetic field dependence of the superconducting gap of ${\text{Cu}}_x{\text{Bi}}_2{\text{Se}}_3$. Finally, we present images and spectroscopy taken with superconducting Nb tips with the refrigerator at 35 mK that indicate that the effective temperature of our tips/sample is approximately 184 mK, corresponding to an energy resolution of 16 $\mu$eV.

References in corpus (4)

• Design and performance of an ultra-high vacuum scanning tunneling microscope operating at dilution refrigerator temperatures and high magnetic fields
• Construction of a Versatile Ultra-Low Temperature Scanning Tunneling Microscope
• A 350 mK, 9 T scanning tunneling microscope for the study of superconducting thin films and single crystals
• Room-temperature tunnel current amplifier and experimental setup for high resolution electronic spectroscopy in millikelvin STM experiments

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