Feedback loop dependent charge density wave imaging by scanning tunneling spectroscopy

TL;DR

This paper compares different scanning tunneling spectroscopy methods for imaging charge density waves, highlighting that constant-height STS accurately maps intrinsic LDOS while constant-current STS can introduce artifacts due to set-point effects.

Contribution

The study demonstrates that only constant-height STS reliably captures the true LDOS in charge density wave imaging, addressing limitations of conventional constant-current STS.

Findings

Constant-height STS accurately maps intrinsic LDOS.

Constant-current STS images are affected by set-point artifacts.

Set-point effects can mislead charge density wave gap identification.

Abstract

Scanning Tunneling Spectroscopy (STS) is a unique technique to probe the local density of states (LDOS) at the atomic scale by measuring the tunneling conductance between a sharp tip and a sample surface. However, the technique suffers of well-known limitations, the so-called set-point effect, which can potentially introduce artifacts in the measurements. We compare several STS imaging schemes applied to the LDOS modulations of the charge density wave state on atomically flat surfaces, and demonstrate that only constant-height STS is capable of mapping the intrinsic LDOS. In the constant-current STS, commonly used and easier-to-implement, the tip-sample distance variations imposed by the feedback loop result in set-point-dependent STS images and possibly mislead the identification of the CDW gap edges.