Evolution of magnetic, transport, and thermal properties in Na${}_{4-x}$Ir${}_3$O${}_8$

Abstract

The hyper-kagome material Na${}_4$Ir${}_3$O${}_8$ is a three-dimensional spin-liquid candidate proximate to a quantum critical point (QCP). We present a comprehensive study of the structure, magnetic susceptibility $\chi$, heat capacity $C$, and electrical transport on polycrystalline samples of the doped hyper-kagome material Na${}_{4-x}$Ir${}_3$O${}_8$ ($x\approx 0,0.1,0.3,0.7)$. Materials with $x\le 0.3$ are found to be Mott insulators with strong antiferromagnetic interactions and no magnetic ordering down to $T=2$ K\@. All samples show irreversibility below $T\approx 6$ K between the zero-field-cooled and field-cooled magnetization measured in low fields ($H=0.050$ T) suggesting a frozen low temperature state although no corresponding anomaly is seen in the heat capacity. The $x=0.7$ sample shows $\rho (T)$ which weakly increases with decreasing temperature $T$, nearly $T$ independent $\chi$, a linear in $T$ contribution to the low temperature $C$, and a Wilson ratio $R_W\approx 7$ suggesting anomalous semi-metallic behavior.

6 pages, 5 figures, 2 tables