Thermoelectric power investigations of YbAgGe across the quantum critical point

The magnetic field and temperature dependences of the thermoelectric power (TEP) of the antiferromagnetically ordered heavy fermion compound YbAgGe are measured across the field-induced quantum critical point. These TEP measurements reproduce the earlier H-T phase diagram and identify an additional domelike phase between similar to 45 and similar to 70 kOe. On the low-field side of this region, H > H(c) similar to 45 kOe, the sign of the TEP changes from negative to positive; on the high-field side of this region, H approximate to 70 kOe, a non-Fermi-liquid state is evidenced as the logarithmic temperature dependence of S(T)/T, in agreement with previous specific heat results C(T)/T alpha-log(T). For higher fields, H > 70 kOe, the observed large value of alpha, S(T) = alpha T, is indicative of the heavy fermion state and shows a correlation with C(T)/T.