Enhanced thermopower in the correlated semimetallic phase of hole-doped pyrochlore iridates

We have investigated the charge transport in the paramagnetic metallic phase of hole-doped pyrochlore iridates. The temperature dependence of thermopower shows a remarkable peak, typically $45\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{V}$/K at 20 K, in a wide doping range from a heavily doped region to nearby the Mott transition. Calculations based on local density approximation and dynamical mean-field theory show the presence of quadratic band touching (QBT) in these compounds. This quantitatively elucidates the thermopower characteristics and specific heat of the doping-induced metallic state, suggesting that QBT is a common and robust feature in the paramagnetic metallic phase of hole-doped pyrochlore iridates even in the proximity of the Mott transition.