Anomalous Thermoelectric Transport and Giant Nernst Effect in Multilayered Massless Dirac Fermion System

We have measured the thermopower and Nernst effect of the multilayered massless Dirac fermion system α-(BEDT-TTF)2I3 under pressure. In the quantum limit region, the extremely large Nernst effect rather than the Seebeck effect was observed. This unusual behavior results from the intrinsic nature of the zero-mode Landau level characteristic of the Dirac fermion system. The possible origin of the giant Nernst signal compared with that of graphene is the sharp width of the Landau level and the Zeeman gap in high-purity α-(BEDT-TTF)2I3 crystal.