Energy-dependent spatial texturing of the charge order in $1T$-Cu$_x$TiSe$_2$

TL;DR

This study reveals how Cu intercalation causes energy-dependent spatial texturing of charge density waves in 1T-Cu_xTiSe_2, with implications for understanding the CDW ground state and its relation to superconductivity.

Contribution

It provides the first atomic-scale characterization of Cu-driven spatial texturing and phase shifts in the charge density wave in 1T-Cu_xTiSe_2, linking local electronic structure to doping.

Findings

Cu intercalation induces energy-dependent CDW patches.

Sharp $c ext{-} ext{ extpi}$DWs occur independently of Cu distribution.

CDW gap features include large amplitude and shift with doping.

Abstract

We report a detailed study of the microscopic effects of Cu intercalation on the charge density wave (CDW) in 1\textit{T}-Cu$_x$TiSe$_2$. Scanning tunneling microscopy and spectroscopy (STM/STS) reveal a unique, Cu driven spatial texturing of the charge ordered phase, with the appearance of energy dependent CDW patches and sharp $\pi$-phase shift domain walls ($\pi$DWs). The energy and doping dependencies of the patchwork are directly linked to the inhomogeneous potential landscape due to the Cu intercalants. They imply a CDW gap with unusual features, including a large amplitude, the opening below the Fermi level and a shift to higher binding energy with electron doping. Unlike the patchwork, the $\pi$DWs occur independently of the intercalated Cu distribution. They remain atomically sharp throughout the investigated phase diagram and occur both in superconducting and non-superconducting specimen. These results provide unique atomic-scale insight on the CDW ground state, questioning the existence of incommensurate CDW domain walls and contributing to understand its formation mechanism and interplay with superconductivity.