Influence of doping on the Hall coefficient in Sr_{14-x}Ca_xCu_24O_41

TL;DR

This study investigates how calcium doping affects the Hall coefficient and carrier distribution in Sr_{14-x}Ca_xCu_24O_41, revealing a transition to behavior similar to high-temperature superconductors at high doping levels.

Contribution

It provides new insights into the carrier dynamics and hole distribution between ladder and chain subsystems as a function of calcium doping in Sr_{14-x}Ca_xCu_24O_41.

Findings

For x<11.5, semiconducting behavior observed.

At x=11.5, Hall coefficient resembles high-Tc cuprates.

Less than 1 hole per formula unit added to ladders at high doping.

Abstract

We present Hall-effect measurements of two-leg ladder compounds Sr_{14-x}Ca_xCu_24O_41 (0 <= x <= 11.5) with the aim to determine the number of carriers participating in dc transport. Distribution of holes between the ladder and chain subsystems is one of the crucial questions important for understanding the physics of these compounds. Our Hall effect and resistivity measurements show typical semiconducting behavior for x < 11.5. However, for x=11.5, the results are completely different, and the Hall coefficient and resistivity behavior is qualitatively similar to that of high temperature copper-oxide superconductors. We have determined the effective number of carriers at room temperature and compared it to the number of holes in the ladders obtained by other experimental techniques. We propose that going from x=0 to x=11.5 less than 1 hole per formula unit is added to the ladders and is responsible for a pronounced change in resistivity with Ca doping.