Influence of the structural modulations and the Chain-ladder interaction in the $Sr\_{14-x}Ca\_{x}Cu\_{24}O\_{41}$ compounds

TL;DR

This study investigates how structural modulations and chain-ladder interactions influence the electronic properties of Sr14-xCaxCu24O41 compounds, revealing significant orbital energy modulations and negligible chain-ladder coupling, with implications for superconductivity.

Contribution

The paper provides the first ab-initio derived $t-J$ model incorporating incommensurate structural modulations in Sr14-xCaxCu24O41 compounds, highlighting the modulation effects on orbital energies and chain-ladder interactions.

Findings

Orbital energies are strongly modulated along ladder legs in highly calcium-doped samples.

Sites on ladder rungs are iso-energetic, suggesting hole delocalization on rungs.

Chain-ladder interactions are negligible in these compounds.

Abstract

We studied the effects of the incommensurate structural modulations on the ladder subsystem of the $Sr\_{14-x}Ca\_{x}Cu\_{24}O\_{41}$ family of compounds using ab-initio explicitly-correlated calculations. From these calculations we derived $t-J$ model as a function of the fourth crystallographic coordinate $\tau$ describing the incommensurate modulations. It was found that in the highly calcium-doped system, the on-site orbital energies are strongly modulated along the ladder legs. On the contrary the two sites of the ladder rungs are iso-energetic and the holes are thus expected to be delocalized on the rungs. Chain-ladder interactions were also evaluated and found to be very negligible. The ladder superconductivity model for these systems is discussed in the light of the present results.