Insensitivity of the striped charge-orders in IrTe$_2$ to alkali surface doping implies their structural origin

TL;DR

This study shows that surface potassium doping does not affect the charge-ordering transitions in IrTe$_2$, indicating these phases are primarily driven by structural factors rather than electronic doping.

Contribution

It demonstrates that charge-order phases in IrTe$_2$ are insensitive to surface electron doping, highlighting the structural origin of these phases.

Findings

Charge order transition temperatures remain unchanged with K doping.

Stripe periodicity is unaffected by potassium surface doping.

Charge order stability is due to structural effects, not electronic doping.

Abstract

We present a combined angle-resolved photoemission spectroscopy and low-energy electron diffraction (LEED) study of the prominent transition metal dichalcogenide IrTe$_2$ upon potassium (K) deposition on its surface. Pristine IrTe$_2$ undergoes a series of charge-ordered phase transitions below room temperature that are characterized by the formation of stripes of Ir dimers of different periodicities. Supported by density functional theory calculations, we first show that the K atoms dope the topmost IrTe$_2$ layer with electrons, therefore strongly decreasing the work function and shifting only the electronic surface states towards higher binding energy. We then follow the evolution of its electronic structure as a function of temperature across the charge-ordered phase transitions and observe that their critical temperatures are unchanged for K coverages of $0.13$ and $0.21$~monolayer (ML). Using LEED, we also confirm that the periodicity of the related stripe phases is unaffected by the K doping. We surmise that the charge-ordered phase transitions of IrTe$_2$ are robust against electron surface doping, because of its metallic nature at all temperatures, and due to the importance of structural effects in stabilizing charge order in IrTe$_2$.