Polarized Raman spectroscopy study of metallic $(Sr_{1-x}La_{x})_{3}Ir_{2}O_{7}$: a consistent picture of disorder-interrupted unidirectional charge order

TL;DR

This study uses polarized Raman spectroscopy to investigate charge order in metallic $(Sr_{1-x}La_{x})_{3}Ir_{2}O_{7}$, revealing symmetry breaking, short-range domains, and disorder effects across temperature and doping levels.

Contribution

It provides a detailed characterization of charge order symmetry, domain structure, and disorder effects in a metallic iridate, linking these features to similar phenomena in cuprate superconductors.

Findings

Charge order breaks fourfold symmetry into twofold.

Charge order forms short-range domains with rotated wave vectors.

Charge order mode frequency remains nearly constant with temperature and doping.

Abstract

We have used rotational anisotropic polarized Raman spectroscopy to study the symmetries, the temperature and the doping dependence of the charge ordered state in metallic $(Sr_{1-x}La_{x})_{3}Ir_{2}O_{7}$. Although the Raman probe size is greater than the charge ordering length, we establish that the charge ordering breaks the fourfold rotational symmetry of the underlying tetragonal crystal lattice into twofold, as well as the translational symmetry, and forms short-range domains with $90^{\circ}$ rotated charge order wave vectors, as soon as the charge order sets in below $T_{CO} = \sim$ 200K and across the doping-induced insulator metal transition. We observe that this charge order mode frequency remains nearly constant over a wide temperature range and up to the highest doping level. These above features are highly reminiscent of the ubiquitous unidirectional charge order in underdoped high-$T_C$ copper-oxide-based superconductors (cuprates). We further resolve that the charge order damping rate diverges when approaching $T_{CO}$ from below and increases significantly as increasing the La doping level, which resembles the behaviors for a disorder-interrupted ordered phase and has not been observed for the charge order in cuprates.