# The study of intrinsic defect state of FeSe with scanning tunneling microscopy

## TL;DR

This study uses high-resolution scanning tunneling microscopy to identify and analyze intrinsic defect states in bulk FeSe, providing detailed defect mapping that supports future theoretical modeling.

## Contribution

The paper presents a comprehensive identification and analysis of intrinsic defect types in FeSe using STM and spectroscopy, confirmed by electron microscopy.

## Key findings

- Identified Fe vacancy and Se$_ ext{Fe}$ defect as type I and II dumbbells.
- Mapped defect states across a large energy range.
- Confirmed defect types with electron microscopy.

## Abstract

We apply high resolution scanning tunneling microscopy to study intrinsic defect states of bulk FeSe. Four types of intrinsic defects including the type I dumbbell, type II dumbbell, top-layer Se vacancy and inner-layer Se-site defect are extensively analyzed by scanning tunneling spectroscopy. From characterized depression and enhancement of density of states measured in a large energy range, the type I dumbbell and type II dumbbell are determined to be the Fe vacancy and Se$_\mathrm{Fe}$ defect, respectively. The top-layer Se vacancy and possible inner-layer Se-site vacancy are also determined by spectroscopy analysis. The determination of defects are compared and largely confirmed in the annular dark-field scanning transmission electron microscopy measurement of the exfoliated FeSe. The detailed mapping of defect states in our experiment lays the foundation for a comparison with complex theoretical calculations in the future.