Atomically resolved low-temperature scanning tunneling microscope operating in a 22 T water-cooled magnet

Area of Science:

• Materials Science
• Condensed Matter Physics
• Instrumentation

Background:

• Scanning Tunneling Microscopy (STM) is crucial for atomic-scale surface analysis.
• High magnetic fields and low temperatures present significant challenges for STM operation due to interference and vibrations.
• Existing STM designs struggle to maintain stability and resolution under extreme conditions.

Purpose of the Study:

• To design and construct a novel nonmetallic STM capable of operating in ultra-high magnetic fields.
• To achieve stable, atomic-resolution imaging and spectroscopy at cryogenic temperatures (1.8 K) and high magnetic fields (22 T).
• To demonstrate the instrument's performance on material surfaces like graphite and NbSe2.

Main Methods:

• Developed a nonmetallic (sapphire) tip-sample mechanical loop to minimize magnetic field interference.
• Integrated a spider-drive motor, stand-alone scanner, and moveable sample holder within a liquid helium cryostat.
• Employed a two-stage spring suspension system to isolate the STM head from magnet-induced vibrations.
• Separated the tip-sample mechanical loop from the motor post-tunneling current detection to prevent electrical interference.

Main Results:

• Achieved atomically resolved STM images of graphite at 0 T and 22.8 T at room temperature.
• Obtained atomic-resolution images of NbSe2 at 1.8 K and 22 T.
• Acquired high-resolution dI/dV spectra at temperatures from 1.8 K to 8.5 K and magnetic fields from 0 T to 22 T.
• Demonstrated stable STM operation in a 22 T water-cooled magnet at 1.8 K.

Conclusions:

• This work presents the first STM capable of atomic-resolution imaging and dI/dV measurements at 1.8 K in a 22 T water-cooled magnet.
• The nonmetallic design and mechanical decoupling provide high immunity to magnetic fields, enabling STM applications in ultra-high magnetic field environments.
• The developed STM is a powerful tool for investigating quantum phenomena and material properties under extreme conditions.