Technique for anisotropic extension of organic crystals: Application to temperature dependence of electrical resistance

Abstract

We have developed a technique for the anisotropic extension of fragile molecular crystals. The pressure medium and the instrument, which extends the pressure medium, are both made from epoxy resin. Since the thermal contraction of our instrument is identical to that of the pressure medium, the strain applied to the pressure medium has no temperature dependence down to 2 K. Therefore, the degree of extension applied to the single crystal at low temperatures is uniquely determined from the degree of extension in the pressure medium and thermal contractions of the epoxy resin and the single crystal at ambient pressure. Using this novel instrument, we have measured the temperature dependence of the electrical resistance of metallic, superconducting, and insulating materials. The experimental results are discussed from the viewpoint of the extension (compression) of the lattice constants along the parallel (perpendicular) direction.

Partial Substitution of Ag(I) for Cu(I) in Quantum Spin Liquid κ-(ET)2Cu2(CN)3, Where ET Is Bis(ethylenedithio)tetrathiafulvalene

“…We then sought to partially substitute the Cu­(I) (0.91 Å for a six-coordinate system) with a larger coinage metal (group 11 element), Ag­(I) (1.29 Å for a six-coordinate system), in the anionic layer to expand the crystal lattice, because there is no practical way to apply negative pressure by physical means, except in some cases. − One of the objectives of this study is to investigate the relationship between the composition ratio (i.e., Ag/Cu ratio) and the molecular packing motif. Notably, our recent work shows that the complete substitution, κ-(ET) 2 Ag 2 (CN) 3 (hereafter termed κ -Ag ), which also exhibits QSL behavior, has a key-on-rim-type key–keyhole relationship (Figure b), in contrast to the key-on-hole-type one in κ -Cu .…”

Ambient-Pressure Organic Superconductor κ-(ET)2Ag(CN)[N(CN)2] Formed with Polymeric Silver(I) Complex Anion

“…This, as well as the enhanced electron correlation, should favor the increase in the superconducting critical temperature (Tc) within a BCS-like picture where Tc is controlled by the density of states at the Fermi level (D(EF)). 12) Considering the fact that there is no practical way of applying negative pressure by physical means, except in special cases, [13][14][15] a chemical modification such as Ag(I) substitution in the 10 K-class superconductors is an obvious target. However, no such materials have been found to date, whereas several ambient-pressure ET superconductors composed of Ag(I) anions, such as polymeric [Ag(CN)2 -]∞ (midpoint Tc = 5.0 K) 16) and discrete Ag(CF3)4 -(onset Tc = 2.4-11.1 K, depending on the solvent molecules), [17][18][19] have been reported.…”