13C NMR Study on Zero-Gap State in the Organic Conductor θ-(BEDT-TTF)2I3 under Pressure

Abstract

We present the results of our 13 C NMR study of the quasi-two-dimensional organic conductor θ-(BEDT-TTF) 2 I 3 under pressure, which is suggested to be a zero-gap conductor by transport measurements. We found that NMR spin shift is proportional to T and that spin–lattice relaxation rate follows the power law T α (α=3–4), where T is the temperature. This behavior is consistent with the cone-like band dispersion and provides microscopic evidence for the realization of the zero-gap state in the present material under pressure.