Superconductivity and Charge Ordering in BEDT-TTF Based Organic Conductors with β″-Type Molecular Arrangement

Abstract

Exotic superconductivity that appears near the charge ordering instability has attracted significant interest since the beginning of superconducting study. The discovery of possible coexistence of charge ordering and superconductivity in cuprates and kagome metals has further fascinated researchers in recent years. In this review, we focus on the BEDT-TTF-based organic superconductor with β″-type molecular packing sequence, which shows the charge ordering transition in the very vicinity of superconducting transition, and summarize the experimental results reported up to the present. At the charge ordering temperature, ultrasonic measurement detects the softening of the crystal lattice, and 13C-NMR measurement shows an increase in nuclear spin-lattice relaxation rate divided by temperature 1/T1T. These results suggest that low-energy dynamics are activated near the charge ordering transition, leading us to invoke the charge-fluctuation mediated superconducting pairing mechanism.

Introduction of new guest molecules into BEDT-TTF radical-cation salts with tris(oxalato)ferrate

“…The shape, the size, and the orientation of the guest molecule within the anion layer all influence the packing and the disorder of the ethylene groups of adjacent donors which has a marked effect on the conducting behaviour and can destabilise the superconducting transition. 16 Using guest molecules close in size to benzonitrile gives isostructural β″-(BEDT-TTF) 4 [(H 3 O)Fe(C 2 O 4 ) 3 ]•guest salts whose cell parameters can be correlated with the conducting properties. 17 The superconducting Tc is shown to increase with increasing length of the b axis.…”

New charge-transfer complexes of 1,2,5-chalcogenadiazoles with tetrathiafulvalenes

“…3 Despite a long history of studying intermolecular interactions, including those in crystalline CT complexes, a higher-accuracy numerical treatment, particularly based on energy decomposition analysis, has only recently been exploited as an option. 4,5 Tetrathiafulvalenes (TTFs) and 1,2,5-chalcogenadiazoles (chalcogen = S, Se, Te) belong to the most frequently exploited D 3,[6][7][8][9][10] and A [11][12][13][14][15][16][17] families, respectively. The electron-accepting ability of 1,2,5-chalcogenadiazoles is caused by positive electron affinity meaning that their radical anions (RAs) are thermodynamically more preferable than neutral molecules.…”

“…Tetrathiafulvalenes (TTFs) and 1,2,5-chalcogenadiazoles (chalcogen = S, Se, Te) belong to the most frequently exploited D 3,6–10 and A 11–17 families, respectively. The electron-accepting ability of 1,2,5-chalcogenadiazoles is caused by positive electron affinity meaning that their radical anions (RAs) are thermodynamically more preferable than neutral molecules.…”

A triad molecular conductor: simultaneous control of charge and molecular arrangements

“…In the development of new molecular superconductors, the molecular metals adjacent to the charge-ordered insulating (COI) states have attracted considerable attention, because the COI states often turn into superconducting states with rather high-T C s by slight physical and/or chemical modifications. [1][2][3][4][5] In particular, mixed crystals composed of different component molecules are of significant interest because there is a possibility to control the COI states by their different electron-donating properties. 6 However, it is imposssible to prepare a mixed crystal composed of different component molecules, where the molecular arrangements are finely controlled three-dimensionally to achieve designed conducting properties and charge distributions.…”