Thermodynamic Properties of κ-(BEDT-TTF)2X Salts: Electron Correlations and Superconductivity

Abstract

Abstract:Heat capacity measurements of κ-(BEDT-TTF) 2 X (BEDT-TTF: Bis(ethylendithio) tetrathiafulvalene, X: counteranions) which are classified as two-dimensional (2D) dimer-Mott system are reported. At first, we explain structural and electronic features originated from rigid dimerization in donor arrangement in 2D layers. The antiferromagnetic Mott insulating phase located at low-pressure region in the phase diagram shows vanishing γ electronic heat capacity coefficient in the heat capacity, which claims opening of a charge-gap in this insulating state. Then, a systematic change of the γ around the Mott boundary region is reported in relation to the glass freezing of ethylene dynamics. The thermodynamic parameters determined by ∆C p /γT c of 10 K class superconductors, κ-(BEDT-TTF) 2 Cu(NCS) 2 and κ-(BEDT-TTF) 2 Cu[N(CN) 2 ]Br demonstrate that a rather large gap with a strong coupling character appears around the Fermi-surface. On the other hand, the low temperature heat capacity clearly shows a picture of nodal-gap structure due to an anisotropic pairing. The comparison with lower T c compounds in the κ-type structure is also performed so as to discuss overall features of the κ-type superconductors. The heat capacity measurements of hole-doped systems containing mercury in the counteranions show an anomalous enhancement of γ, which is consistent with the T 1 −1 of NMR experiments etc. The results of heat capacity measurements under high pressures are also reported. OPEN ACCESSCrystals 2012, 2 742

Thermodynamics of a Liquid-like Spin State in Molecule-based Magnets with Geometric Frustrations

“…5 Recently, an unusual liquid-like state of spins was observed in organic charge-transfer salts with triangle lattice structures. Intensive investigations have been undertaken to unveil its origins and to produce further new magnetic states.…”

“…3,4 Moreover, thermodynamic measurements at low temperatures can clarify the nature of the ground states, since it is possible to extract spectroscopic information on the low-energy excitation spectrum from them. 5 Recently, an unusual liquid-like state of spins was observed in organic charge-transfer salts with triangle lattice structures. Intensive investigations have been undertaken to unveil its origins and to produce further new magnetic states.…”

“…9 Numerous insulating compounds which have AF-ordered ground states or chargeordered ground states show vanishing £. 4,5 The heat capacity data of κ-(BEDT-TTF) 2 2 ]Br, and β¤-(BEDT-TTF) 2 ICl 2 , typical Mott insulating compounds, are shown for reference in Figure 4a. They all show 3D AF ordering around 2030 K and superconductivity at lower temperatures under pressure.…”

Crystal growth of the layered organic antiferromagnet, deuterated κ-(BEDT-TTF)2Cu[N(CN)2]Br

“…When the intra-dimer Coulomb repulsion U is larger than the width of the band constructed by the interdimer transfer integrals W, the system becomes a Mott insulating state with an antiferromagnetic ground state. On the contrary, if U < W, the system becomes a superconducting state [3]. No study has reported clearly on the synthesis of this material, although a good quality of this single crystal is required for precise magnetization measurement.…”

“…Right now, β'-(BEDT-TTF)2ICl2 under 8.2 GPa has the highest critical temperature, Tc of 14.2 K for an organic superconductor [2]. The κ-(BEDT-TTF) 2Cu [N (CN) 2] Br (denoted as d8-κ-Br) consists of alternating layers of conducting donor, and it has a superconducting transition temperature, Tc of 11.5 K [3]. d8-κ-Br which eight hydrogens in an ethylene group of BEDT-TTF (bis (ethylene dithiol) tetrathiafulvalene) are substituted by deuteriums.…”