Atomically resolved probe-type scanning tunnelling microscope for use in harsh vibrational cryogen-free...

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Superconducting magnet systems typically generate significant vibrations, hindering atomic-resolution measurements.
• Cryogen-free cooling systems, while convenient, present environmental challenges for sensitive instrumentation.

Purpose of the Study:

• To design and demonstrate a scanning tunnelling microscope (STM) capable of atomic resolution within a harsh, cryogen-free superconducting magnet.
• To overcome the limitations of vibrational noise and extreme temperatures in superconducting magnet environments.

Main Methods:

• A probe-type STM was integrated into a variable temperature insert (VTI) within an 8 T superconducting magnet.
• The system was cooled to 1.6 K using a pulse-tube cryocooler.
• Atomic resolution imaging and scanning tunnelling spectroscopy (STS) were performed on graphite and NbSe2.

Main Results:

• Atomically resolved images of graphite and NbSe2 were obtained.
• Scanning tunnelling spectra (dI/dV) revealed the temperature-dependent formation of the superconducting gap in NbSe2 near its critical temperature.
• Low drifting rates (1.15 pm/min X-Y, 1.71 pm/min Z) and minimal current noise (1.5 pA.Hz^-1/2) were achieved at 1.6 K.

Conclusions:

• The developed STM successfully operates with atomic resolution in a challenging cryogen-free superconducting magnet system.
• This work demonstrates the feasibility of high-precision measurements in environments previously considered too harsh.
• The results pave the way for advanced studies of superconductivity and material properties under extreme conditions.