Correlation in transport coefficients of hole-doped CuRhO₂ single crystals

To clarify the origin of the nontrivial thermoelectric properties observed in the delafossite oxide CuRhO$_2$ polycrystals, we have performed the systematic transport measurements on the single-crystalline CuRhO$_2$ samples. In the parent compound, we find a pronounced peak structure due to a phonon-drag effect in the temperature dependence of the Seebeck coefficient, which is also confirmed by the size effect experiments. In the Mg-substituted crystals, in contrast to the results of the polycrystals, both the resistivity and the Seebeck coefficient decrease with increasing Mg content $y$. In particular, the coefficient $A$ for the $T^2$ term of the resistivity and the $T$-linear coefficient for the Seebeck coefficient at low temperatures are well described within a simple relationship expected for metals, which is also applicable to the correlated materials with low carrier densities.