$^{13}$C NMR Study on Zero-Gap State in the Organic Conductor $θ$-(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 $θ$-(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 $T^α$ ($α=3 \sim 4$), 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