Off-diagonal thermoelectric effect and its gate tuning in molecular conductor κ-(BEDT-TTF)2Cu[N(CN)2]Cl

We report on the off-diagonal (transverse) thermoelectric effect in the molecular conductor κ-(BEDT-TTF)2Cu[N(CN)2]Cl, originating from the coexistence of the two-dimensional hole-like and one-dimensional electron-like Fermi surfaces. The off-diagonal thermoelectric voltage corresponds to the anisotropy of the Seebeck coefficient and is proportional to the sample length perpendicular to the temperature gradient, reaching ∼90 μV/K in our sample. Also, we investigated the effect of electric-double-layer doping on the off-diagonal thermoelectric effect. Under hole doping, while the resistance significantly decreases, the off-diagonal Seebeck coefficient does not decrease probably because of pseudogap formation. As a result, hole doping increases the off-diagonal power factor by up to a factor of approximately 15 at the doped surface.