Anisotropic Charge Modulation in Ladder Planes of Sr_14-xCa_xCu_24O_41

TL;DR

This study investigates the anisotropic charge modulation in Sr_14-xCa_xCu_24O_41, revealing directional dependence of charge-density wave modes and the dominance of hopping conduction perpendicular to the ladder planes.

Contribution

It provides detailed characterization of charge-density wave behavior and anisotropic charge response in Sr_14-xCa_xCu_24O_41 across different calcium doping levels.

Findings

Charge-density wave modes observed along rungs and legs vary with doping.

Charge response along rungs vanishes at high doping levels.

Perpendicular transport is dominated by hopping conduction.

Abstract

The charge response of the ladders in Sr_14-xCa_xCu_24O_41 is characterized by dc resistivity, low frequency dielectric and optical spectroscopy in all three crystallographic directions. The collective charge-density wave screened mode is observed in the direction of the rungs for x=0, 3 and 6, in addition to the mode along the legs. For x=8 and 9, the charge-density-wave response along the rungs fully vanishes, while the one along the legs persists. The transport perpendicular to the planes is always dominated by hopping.