# Systematic Raman study of optical phonons in $R$Ba$_2$Cu$_3$O$_{6+\delta}$ ($R$ = Y, Dy, Gd, Sm, Nd): Antiferromagnetic coupling strength versus lattice parameters

## TL;DR

This study systematically investigates how lattice parameters influence optical phonon energies and antiferromagnetic coupling strength in RBa2Cu3O6+δ cuprates, revealing new insights into their structural and magnetic properties.

## Contribution

It provides a comprehensive analysis of the relationship between lattice parameters, phonon energies, and magnetic coupling in various R-123 cuprates, highlighting unexpected independence of J from lattice parameter a.

## Key findings

- Phonon energy relates systematically to inverse lattice parameter a.
- Temperature-dependent phonon splitting observed in Nd-123 at low doping.
- J is independent of lattice parameter a for the first four R families.

## Abstract

We present a systematic study of the interplay between lattice parameters and the energy of the optical phonons as well as the antiferromagnetic coupling strength, $J$, in the high-$T_{\text{c}}$ superconducting cuprate $R$Ba$_2$Cu$_3$O$_{6+\delta}$ (\mbox{R-123}, $R =$ Y, Dy, Gd, Sm, Nd) with hole-doping $p$ ($0.00<p \lesssim 0.04$). The energy of the $B_{1g}$-mode at $\nu_{B1g}\approx~335$ cm$^{-1}$ has been found to relate systematically to the inverse of the lattice parameter $a$. Our results confirm the temperature dependent phonon splitting for Nd-123 at low doping, which has been reported for optimally-doped Nd-123. Surprisingly, $J$ is independent of $a$ for the first four $R$ families, and a general consistency between $T_{\text{c}}^{\text{max}}$ and $J$, as suggested in a previous investigation, could not be confirmed.