Charge order induced sharp Raman peak in Sr_14Cu_24O_41

TL;DR

This paper explains how charge order in Sr_14Cu_24O_41 causes a sharp Raman peak by inducing a gap in magnetic excitations, revealing charge distribution and order periodicity.

Contribution

It demonstrates that charge order-induced gaps significantly alter the magnetic Raman spectrum in Sr_14Cu_24O_41, linking spectral features to charge distribution.

Findings

Charge order causes a sharp Raman peak in Sr_14Cu_24O_41.

Charge order induces a gap in magnetic excitation spectrum.

Broader spectrum in La_6Ca_8Cu_24O$_41$ indicates absence of charge order.

Abstract

In the two-leg S=1/2 ladders of Sr_14Cu_24O_41 a modulation of the exchange coupling arises from the charge order within the other structural element, the CuO_2 chains. In general, breaking translational invariance by modulation causes gaps within the dispersion of elementary excitations. We show that the gap induced by the charge order can drastically change the magnetic Raman spectrum leading to the sharp peak observed in Sr_14Cu_24O_41. This sharp Raman line gives insight in the charge-order periodicity and hence in the distribution of carriers. The much broader spectrum of La_6Ca_8Cu_24O$_41 reflects the response of an undoped ladder in the absence of charge order.