Hole redistribution in Sr\_(14-x)Ca\_xCu\_24O\_41 (x = 0, 12) spin ladder compounds: ^63Cu and ^17O NMR study under pressure

TL;DR

This study uses ^63Cu and ^17O NMR to analyze how pressure, temperature, and calcium doping affect hole distribution in Sr extsubscript{14-x}Ca extsubscript{x}Cu extsubscript{24}O extsubscript{41} spin ladder compounds, linking hole concentration to superconductivity.

Contribution

It provides detailed insights into hole redistribution mechanisms under pressure and doping, highlighting the role of increased hole concentration in stabilizing superconductivity in these compounds.

Findings

Hole density increases with temperature, Ca content, and pressure.

Estimated 0.10 holes per Cu at low temperature in Ca12 under 32 kbar.

High pressure enhances hole concentration in CuO extsubscript{2} planes, promoting superconductivity.

Abstract

We report the results of a ^63Cu and ^17O NMR study of the nuclear quadrupole interaction tensor, ^(17,63)nu\_{Q,alpha}, in the hole doped spin ladder system Sr\_(14-x)Ca\_xCu\_24O\_41 (x = 0 and 12) performed under ambient and high pressures. NMR data show that the hole density in the Cu\_2O\_3 ladder layer grows with temperature, Ca content and an applied pressure. We have derived the hole occupation of Cu 3d and O 2p orbitals at the different ion sites in the Cu\_2O\_3 ladder as a function of the temperature, Ca substitution and pressure. We also suggest that the most important role of high pressure for the stabilization of a superconducting ground state in Ca-rich two-leg ladders is an increase of the hole concentration in the conducting Cu\_2O\_3 planes. We have obtained an estimate of 0.10 hole per Cu1 for the hole concentration at low temperature in Ca12 under 32 kbar when this compound undergoes a superconducting transition at 5K. Such a value fits fairly well with the doping phase diagram of cuprate superconductors.