${}^{13}$C NMR Study on Zero-Gap State in the Organic Conductor $\theta$-(BEDT-TTF)${}_2$I${}_3$ under Pressure

Abstract

We present the results of our ${}^{13}$C NMR study of the quasi-two-dimensional organic conductor $\theta$-(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 $T^{\alpha }$ ($\alpha =3\sim 4$), 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.

4 pages, 4 figures, to be published in J. Phys. Soc. Jpn. vol.79 No.6