Novel Dielectric Anomaly in the Hole-Doped ${\mathrm{L}\mathrm{a}}_2{\mathrm{C}\mathrm{u}}_{1-x}{\mathrm{L}\mathrm{i}}_x{\mathrm{O}}_4$ and ${\mathrm{L}\mathrm{a}}_{2-x}{\mathrm{S}\mathrm{r}}_x{\mathrm{N}\mathrm{i}\mathrm{O}}_4$ Insulators: Signature of an Electronic Glassy State

The low-frequency dielectric response of hole-doped insulators ${\mathrm{L}\mathrm{a}}_2{\mathrm{C}\mathrm{u}}_{1-x}{\mathrm{L}\mathrm{i}}_x{\mathrm{O}}_4$ and ${\mathrm{L}\mathrm{a}}_{2-x}{\mathrm{S}\mathrm{r}}_x{\mathrm{N}\mathrm{i}\mathrm{O}}_4$ shows a large dielectric constant ${\epsilon }^{\prime }$ at high temperature and a steplike drop by a factor of 100 at a material-dependent low temperature $T_f$. $T_f$ increases with frequency, and the dielectric response shows universal scaling in a Cole-Cole plot, suggesting that a charge-glass state is realized both in the cuprates and in the nickelates.

Figure 1

The complex dielectric constant of ${\mathrm{L}\mathrm{a}}_2{\mathrm{C}\mathrm{u}}_{1-x}{\mathrm{L}\mathrm{i}}_x{\mathrm{O}}_4$ ($x=0.023$) versus $T$. Solid lines are results from the defect model (see text).

Figure 2

(a) ${\epsilon }^{\prime \prime }$ of ${\mathrm{L}\mathrm{a}}_2{\mathrm{C}\mathrm{u}}_{1-x}{\mathrm{L}\mathrm{i}}_x{\mathrm{O}}_4$ ($x=0.023$) versus ${\epsilon }^{\prime }$ for the $E\parallel c$ axis. The solid line is from the Davidson-Cole analysis with $\beta =0.9$. (b) Frequency versus $T_f$ obtained from the Cole-Cole arc.

Figure 3

(a) ${\epsilon }^{\prime }$ of ${\mathrm{L}\mathrm{a}}_{2-x}{\mathrm{S}\mathrm{r}}_x{\mathrm{N}\mathrm{i}\mathrm{O}}_4$ ($x=1/3$) versus $T$ for the $E\parallel ab$ plane. Solid lines are best fits of the defect model. (b) ${\epsilon }^{\prime \prime }$ versus ${\epsilon }^{\prime }$. Solid line is the Cole-Cole arc with $\beta =0.75$.

Figure 4

Magnetic susceptibility $\chi$ vs $T$ for ${\mathrm{L}\mathrm{a}}_2{\mathrm{C}\mathrm{u}}_{1-x}{\mathrm{L}\mathrm{i}}_x{\mathrm{O}}_4$ ($x=0.023$) for the $H\parallel c$ axis. Inset: ${\mathrm{L}\mathrm{a}}_{2-x}{\mathrm{S}\mathrm{r}}_x{\mathrm{N}\mathrm{i}\mathrm{O}}_4$ ($x=1/3$) for the $H\parallel ab$ plane. The FC data of the nickelate are lowered by a constant for comparison. The arrows indicate the deviation temperature between ZFC and FC curves.