$^{13}$C NMR Study on Zero-Gap State in the Organic Conductor $\theta$-(BEDT-TTF)$_{2}$I$_{3}$ under Pressure

TL;DR

This study uses $^{13}$C NMR to provide microscopic evidence of a zero-gap state in the organic conductor $ heta$-(BEDT-TTF)$_2$I$_{3}$ under pressure, revealing characteristic temperature-dependent behaviors.

Contribution

It demonstrates the realization of a zero-gap state in $ heta$-(BEDT-TTF)$_2$I$_{3}$ under pressure through NMR measurements, linking spin properties to band dispersion.

Findings

NMR spin shift is proportional to temperature

Spin-lattice relaxation rate follows a $T^{eta}$ law with $eta=3$ to 4

Evidence supports cone-like band dispersion in the material

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.