Stabilized Optical Scanning Tunneling Microscopy: Probing Defect-Driven Phenomena in Correlated Electron Systems

by Georg Traeger
Doctoral thesis
Date of Examination:2025-10-28
Date of issue:2025-11-26
Advisor:Prof. Dr. Martin apl. Wenderoth
Referee:Prof. Dr. Martin apl. Wenderoth
Referee:Prof. Dr. Thomas Weitz
Persistent Address: http://dx.doi.org/10.53846/goediss-11664

 

 

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Abstract

English

This thesis presents the development and application of a stabilized optical scanning tunneling microscopy (STM) approach that enables controlled, localized optical excitation at the atomic scale. A key advancement is the implementation of grating-coupled plasmonic gold tips combined with active beam stabilization via image recognition, which suppress long-term thermal drift and pointing instabilities that have historically limited optical STM experiments. This method allows surface plasmon polaritons to be launched remotely and adiabatically focused to the tip apex, providing nanometer-scale excitation without far-field illumination of the junction. The technique is applied to the correlated layered material 1T-TaS₂, a prototypical charge density wave (CDW) system exhibiting insulating, metallic, and metastable photo-induced states. Using low-temperature STM and scanning tunneling spectroscopy, we first identify a fully metallic anti-phase boundary embedded within the semiconducting commensurate CDW phase. Under controlled optical excitation, we observe the nucleation and manipulation of CDW domain structures and reveal a correlation between defect sites and the formation of domain wall networks. Additionally, we report the emergence of chiral domain configurations by optically quentching the sample system.
Keywords: Scanning Tunneling Microscopy; Plasmonic Tip; Correlated Electron Systems; Charge Density Waves; 1T-TaS₂; Non-Equilibrium Electronic States; Domain Walls