ChemInform Abstract: From Semiconductor‐Semiconductor Transition (42 K) to the Highest‐Tc Organic Superconductor, ϰ‐(ET)2Cu(N(CN)2)Cl (Tc = 12.5 K).

Abstract

ChemInform Abstract The new title superconductor (space group Pnma, Z=4) is prepared in the same way as the recently prepared isostructural Br salt by electrocrystallization. The chloride salt has band dispersion relations and a Fermi surface practically identical with those of the bromide salt.

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

“…As we previously showed [13], pressure slightly decreases the density of states at the Fermi level in k-Cl. Thus, in the case of the present salt it seems as if the donor layers were subjected to a small applied pressure which suppresses the Mott localization as it occurs in k-Cl [19]. This seems at odds with the crystallographic information since the unit cell volume of k 00 -Cl is larger than those of k 0 -Cl and k-Cl.…”

“…Thus, both geometrical and electronic arguments suggest that the donor layers in the new k 00 -Cl polymorph are slightly compressed with respect to those of k-Cl at ambient pressure. In view of the well known subtle pressure dependence of the conductivity behavior of k-Cl [19] this may well be at the origin of the room temperature metallic conductivity of the new polymorph. In addition, the disorder in the acceptor layers most likely renders the transition to the superconducting state impossible.…”

“…However, they exhibit a wide diversity of electronic properties depending on X. 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].…”

Bandwidth-controlled Mott transition inκ−(BEDT−TTF)2Cu[N(C<

“…30 The pure compound κ-(BEDT-TTF)2Cu[N(CN)2]Cl follows the rise in ρ(T ) down to about 30 K, at lower temperatures the resistivity levels off at a value of approximately 10 3 Ωcm and even shows a slight drop around T = 10 K. This behavior is well documented in literature 31,32,33 and associated with traces of superconductivity induced by internal stress or surface effects. Similar effects are seen in samples with very low Br content x = 15%.…”

Optical properties ofβ″−(ET)2SF5

“…4͒ and -(ET) 2 Cu͓N(CN) 2 ͔Cl (T c ϭ12.8 K at 0.3 kbar͒. 5 More recently, a strategy for the preparation of ET-based superconductors has been pursued based upon the design of large discrete counterions 6 to enhance two-dimensional interactions in the solid state. The -(ET) 2 M(CF 3 ) 4 ͑1,1,2-trichloroethane͒ ͑Ref.…”