Nernst effect in $\mathrm{Nd}{\mathrm{Ba}}_2{\left\{{\mathrm{Cu}}_{1-y}{\mathrm{Ni}}_y\right\}}_3{\mathrm{O}}_{7-\delta }$ $(y=0–0.12)$

In $\mathrm{Nd}{\mathrm{Ba}}_2{\left\{{\mathrm{Cu}}_{1-y}{\mathrm{Ni}}_y\right\}}_3{\mathrm{O}}_{7-\delta }$, magnetic Ni-impurities suppress $T_c$ but at the same time the pseudogap is strongly enhanced. This unique feature makes it an ideal system to study possible relations between the anomalous Nernst effect, superconductivity, and the pseudogap. We present Nernst effect measurements on a series of optimally doped $\left({\mathrm{O}}_7\right)$ and underdoped $\left({\mathrm{O}}_{6.8}\right)$ samples with Ni contents ranging from $y=0\text{to}0.12$. In all samples an onset of the Nernst signal is found at $T^{\nu }>T_c$. For the optimally doped samples $T^{\nu }$ and $T_c$ decrease simultaneously with increasing Ni content. The underdoped samples show a different behavior, i.e., the onset of the Nernst signal is hardly affected by increasing the Ni content from $y=0\text{to}0.03$. Irrespective of the oxygen content, $T^{\nu }$ clearly does not track the enhanced pseudogap temperature $T^{*}$.

Figure 1

(Color online) Typical Nernst signals of a series of optimally doped $\mathrm{Nd}{\mathrm{Ba}}_2{\left\{{\mathrm{Cu}}_{1-y}{\mathrm{Ni}}_y\right\}}_3{\mathrm{O}}_7$. The inset enlarges the contributions to the Nernst signal above $T_c$.

Figure 2

(Color online) Nernst coefficients $\nu$ versus temperature for the pure and three Ni-doped $\left({\mathrm{O}}_7\right)$ single crystals (Ref. 19). Onset temperatures are indicated by arrows.

Figure 3

(Color online) Nernst signal of a series of underdoped $\mathrm{Nd}{\mathrm{Ba}}_2{\left\{{\mathrm{Cu}}_{1-y}{\mathrm{Ni}}_y\right\}}_3{\mathrm{O}}_{6.8}$. The insets show an expanded view of the data.

Figure 4

(Color online) Nernst coefficients $\nu$ of the underdoped compounds (onset temperatures are marked by arrows).

Figure 5

(Color online) Onset temperatures of all samples versus $T_c$. The $T^{*}$ band sketches the pseudogap opening temperatures as estimated from the results of Ref. 12.