Electronic transport properties and structural transformations ofκ−(BEDT−TTF)2Cu[N

Abstract

Formation of an insulating ground state in the salt of -(BEDT-TTF) 2 Cu͓N(CN) 2 ͔I was studied by measuring the temperature dependence of the electronic transport properties ͑the anisotropy of the resistivity, thermopower along the principal in-plane directions, and the Hall effect͒ and the x-ray diffraction patterns. Qualitative agreement of all the transport properties with the metallic state predicted by the band structure calculation was found above 230 K. Transformation to the insulating state proceeds via an intermediate stage between 230 and ϳ100 K, in which the transport properties are affected by localization phenomena in the disordered metallic state. The state is induced by the formation of a commensurate superstructure in the anion layer, leading to a unit cell doubling in the c-direction. The electronic spectrum starts to form a real gap below 100 K, as indicated by the sharp thermopower change, which is mainly related to the destruction of the hole pocket. The gap formation is accompanied by an in-plane resistivity anisotropy increase. This transformation is due to a short-range ordering, with a wave vector close to c*/3, strongly interacting with the electronic system.

Classification of Quasi-Two Dimensional Organic Conductors Based on a New Minimal Model

“…There had already been some experimental reports on the possible twofold structure. [38][39][40] In fact, our earlier calculations suggests the existence of such two-fold magnetic state in this polytype. 41) Another famous family based on BETS molecule, -BETS 2 Fe x Ga 1Àx Cl 4Ày Br y , is a mixed-compound with magnetic anions, FeM À1 4 (M = Cl, Br), to be compared with its -analogue.…”

The first polymorph, κ″-(ET)2Cu[N(CN)2]Cl, in the family of κ-(ET)2Cu[N(CN)2]X (X=Cl, Br, I) radical cation salts

“…The k-Br, k-Br 0.5 Cl 0.5 and k-Br 0.7 Cl 0.3 salts undergo a transition to a superconducting state with T c ¼ 11.4-11.6 K at ambient pressure [15,17,18], whereas k-Cl, k-I, and k-Br 0.9 I 0.1 are semiconductors [16,19,20]. At a pressure of 0.3 kbar k-Cl and k-Br 0.9 I 0.1 become superconductors with T c ¼ 12.8 [16] and 3.5 K [20], respectively, and k-I enters into a superconducting state at 1.2 kbar with T c ¼ 8 K [7,21]. Recently, we reported on another salt with the Cu[N(CN) 2 ]Cl anion (referred to as k 0 -Cl) [13,22] which is isostructural with the k-Cl Mott insulator.…”

“…The family of isostructural orthorhombic k-salts with general formula (ET) 2 Cu[N(CN) 2 ]X, where ET ¼ bis(ethylenedithio)-tetrathiafulvalene and X ¼ Cl, Br, I, Br 1Àx I x , Br 1Àx Cl x (in the following, these salts are designated by their X) was discovered in the 1990s [1][2][3][4][5][6] and has been studied intensively up to now [7][8][9][10][11][12][13]. The quasi-two-dimensional organic superconductors with the highest transition temperature T c at ambient and mild pressure have been found in this family of compounds.…”

Quantum interference and weak localization effects in the interlayer magnetoresistance of layered metals

“…In contrast, in many metallic organic charge-transfer salts, this ratio is as large as one thousand. 39 In both the M = Ga and Cr ͑Y =C 2 H 2 Cl 2 ͒ materials in zero field, the interlayer resistivity increases approximately logarithmically with temperature below about 20 K with a total change of about 1% between 1 and 20 K. 26 At a temperature of 1.5 K, perpendicular fields of about 0.2 and 2 T destroy this feature in the M = Ga and M = Cr materials, respectively. Furthermore, as the field is tilted toward the plane of the layers, there is a small peak in the interlayer resistance versus angle for both the M = Cr and M = Ga material at = / 2.…”