Charge ordering and chemical potential shift in La$_{2-x}$Sr$_x$NiO$_4$ studied by photoemission spectroscopy

TL;DR

This study investigates how the chemical potential shifts with doping and the charge ordering transition in La$_{2-x}$Sr$_x$NiO$_4$ using photoemission spectroscopy, revealing a doping-dependent shift and charge order effects.

Contribution

It provides new insights into the doping-dependent chemical potential shift and charge ordering phenomena in La$_{2-x}$Sr$_x$NiO$_4$ through detailed photoemission measurements.

Findings

Large downward chemical potential shift in high doping regime.

Suppressed shift in low doping regime due to hole segregation.

Vanishing photoemission intensity at the chemical potential below charge ordering temperature.

Abstract

We have studied the chemical potential shift in La$_{2-x}$Sr$_x$NiO$_4$ and the charge ordering transition in La$_{1.67}$Sr$_{0.33}$NiO$_4$ by photoemission spectroscopy. The result shows a large ($\sim$ 1 eV/hole) downward shift of the chemical potential with hole doping in the high-doping regime ($\delta \gtrsim$ 0.33) while the shift is suppressed in the low-doping regime ($\delta \lesssim$ 0.33). This suppression is attributed to a segregation of doped holes on a microscopic scale when the hole concentration is lower than $\delta \simeq 1/3$. In the $\delta = 1/3$ sample, the photoemission intensity at the chemical potential vanishes below the charge ordering transition temperature $T_{\rm CO}=$ 240 K.