Geometric phase analysis of charge density waves and moiré systems

Department of Quantum Matter Physics, University of Geneva, Switzerland

Geometric phase analysis (GPA), the analysis of the spatial variation of the phase of a periodic signal, of high-resolution scanning tunnelling microscope (STM) data has been widely applied to gain insight into the physics of correlated electron systems. In this talk, we will discuss specific examples revealing spatial variations of the charge density wave (CDW) modulation [1], including discommensuration and topological defects, and the observation of the multiband character of the CDW in a transition metal dichalcogenide [2]. We will also discuss that despite the immerse potential of GPA, it should be employed with caution when several fundamental lattices contribute to the image, in particular in twisted heterostructures featuring moiré patterns. In this case, GPA is likely to suggest the presence of chiral displacement and periodic strain fields [3], even if the structure is completely relaxed and without distortions. These delusive fields are subject to change with varying twist angles, which could mislead the interpretation of twist angle dependent properties.

[1] Pásztor, Á et al. Physical Review Research 2019, 1 (3), 033114.
[2] Pásztor, Á et al. Nature Communications 2021, 12 (1), 6037.
[3] Pásztor, Á et al. 2D Materials 2024.