Simultaneous enhancements of thermopower and electrical conductivity in quasi-one-dimensional α -YbAlB4 single crystal

Abstract

We report the thermoelectric properties of valence fluctuating material α-YbAlB4 along a-, b-, and c-axes. The temperature dependence of the Seebeck coefficient for all axes shows negative peaks at around 250 K, which is close to the Kondo scale. Interestingly, the absolute value of the Seebeck coefficient along c-axis (−75 μV K−1 at 250 K) is larger than those along a- and b-axes (−50 μV K−1 at 250 K) although the electrical resistivity along c-axis is about four times lower than those along a- and b-axes. As a result, a very large thermoelectric power factor of ∼14.5 mW m−1 K−2 is realized along c-axis at 200 K, which is ten times larger than those along a- and b-axes. The anisotropies in electrical resistivity and Seebeck coefficient, respectively, have different origins of Fermi surface and the c-f hybridization, realizing the simultaneous enhancements of thermopower and electrical conductivity.