Doping of a One-Dimensional Mott Insulator: Photoemision and Optical Studies of Sr$_2$CuO$_{3+\delta}$

TL;DR

This study investigates how doping affects the spectral and optical properties of a 1D Mott insulator Sr$_2$CuO$_{3}$, revealing increased bandwidth and separated spinon-holon features without metallic transition.

Contribution

It provides detailed experimental insights into doping effects on a 1D Mott insulator using photoemission and optical spectroscopy, highlighting the persistence of the insulating state.

Findings

Doping reduces the single-particle gap but does not induce metallicity.

Charge-transfer bandwidth increases with doping, while the optical gap remains unchanged.

Separated spinon and holon branches are observed in doped samples.

Abstract

The spectral properties of a one-dimensional (1D) single-chain Mott insulator Sr$_2$CuO$_{3}$ have been studied in angle-resolved photoemission and optical spectroscopy, at half filling and with small concentrations of extra charge doped into the chains via high oxygen pressure growth. The single- particle gap is reduced with oxygen doping, but the metallic state is not reached. The bandwidth of the charge-transfer band increases with doping, while the state becomes narrower, allowing unambiguous observation of separated spinon and holon branches in the doped system. The optical gap is not changed upon doping, indicating that a shift of chemical potential rather than decrease of corelation gap is responsible for the apparent reduction of the photoemission gap.