Thermoelectric power of MgB_2-xBe_x

We investigated thermoelectric power S(T) of MgB_2-xBe_x (x=0, 0.2, 0.3, 0.4, and 0.6) S(T) decreases systematically with x, suggesting that the hole density increases. Our band calculation shows that the increase occurs in the σ band. With the hole doping, T_c decreases. Implication of this phenomenon is discussed within the BCS framework. While the Mott formula explains only the linear part of S(T) at low temperature, incorporation of electron-phonon interaction enables us to explain S(T) over wide temperature range including the anomalous behavior at high temperature.