¹³C NMR measurement of θ-(BEDT-TTF)₂I₃ in non-Fermi liquid region

The BEDT-TTF salts with θ-type molecular arrangement, θ-(BEDT-TTF)₂X, which have a triangular lattice show a wide verity of electronic states (charge order insulator, charge glass state, metal) according to monovalent anion, X. Among them, the X=I₃ salt is considered to be in a typical metal because quantum oscillations are observed at low temperatures [1]. On the other hand, in the optical spectrum, normal Drude response was not observed above 100 K. So the salt is different from a simple Fermi liquid picture at high temperature [2]. Recently, we report increase of resistance noise near 50 K-180 K, where the resistance exceeds the Mott limit [2,3]. In this study, the ¹³C NMR spectra and the 1/T₂, which captures slow fluctuations in the order of kHz were measured. In the salt showing charged glass, the 1/T₂ has a peak, which is thought to be associated with the glass formation process [4]. On the other hand, in X=I₃ salt, the temperature dependence of 1/T₂ is very weak and the absolute value remained small. There was also no significant increase in linewidth. This means that the spectral density of fluctuation in the kHz range is small. [1] M. Tamura et al., JPSJ (1994). [2] K. Takenaka et al., PRL (2005). [3] T. Sato et al., Nat. Mat. (2019). [4] K. Miyagawa et al., JPSJ (2019).