Dimensional crossover and anomalous magnetoresistivity in single crystals $Na_xCoO_2$

TL;DR

This study investigates the resistivity and magnetoresistivity of Na_xCoO_2 single crystals, revealing a dimensional crossover from 2D to 3D with Na content and evidence of spin ordering orientation changes at low temperatures.

Contribution

It provides systematic measurements of resistivity and magnetoresistivity in Na_xCoO_2, highlighting a dimensional crossover and field-induced spin ordering orientation transitions.

Findings

Dimensional crossover from 2D to 3D with decreasing Na content.

Angular magnetoresistivity shows d-wave and p-wave symmetries at different temperatures.

Evidence of spin ordering orientation change below 20 K.

Abstract

The in-plane ($\rho_{ab}$) and c-axis ($\rho_c$) resistivities, and the magnetoresistivity of single crystals $Na_xCoO_2$ with x = 0.7, 0.5 and 0.3 were studied systematically. $\rho_{ab}(T)$ shows similar temperature dependence between $Na_{0.3}CoO_2$ and $Na_{0.7}CoO_2$, while $\rho_c(T)$ is quite different. A dimensional crossover from two to three occurs with decreasing Na concentration from 0.7 to 0.3. The angular dependence of in-plane magnetoresistivity for 0.5 sample shows a \emph{"d-wave-like"} symmetry at 2K, while the \emph{"p-wave-like"} symmetry at 20 K. These results give an evidence for existence of a \emph{spin ordering orientation} below 20 K turned by external field, like the stripes in cuprates.