ESR Characterization of the Organic Superconducting Salts of the BEDT-TTF Donor Molecule with the Novel Organometallic Anion [Cu(CF3)4]- [BEDT-TTF = Bis(ethylenedithio)tetrathiafulvalene

Abstract

Two new organic superconductors and a semiconductor were the subject of angular- and temperature-dependent ESR (electron spin resonance) studies. The-T{sub c}(4.0 K) K{sub L}-(ET){sub 2}Cu(CF{sub 3}){sub 4}(TCE) phase gave room-temperature line widths and g values between 68 ({delta}H{sub {parallel}}) and 2.0097 (g{sub {perpendicular}}), respectively. Its low-temperature behavior can be qualitatively correlated to four-probe resistivity measurements and described with the use of Elliott`s formula. The high-T{sub c} (9.2 K) k{sub H{sup {minus}}}(ET){sub 2}Cu(CF{sub 3}){sub 4}(TCE) phase gave a narrow line width range of 6.2 ({Delta}H{sub {parallel}}) to 5.8 ({Delta}H{sub {perpendicular}}) G and corresponding g values of 2.0081 (g{sub {parallel}}) to 2.0105 (g{perpendicular}), respectively. The solvent-free semiconductor (ET){sub 2}Cu(CF{sub 3}){sub 4} revealed a characteristic line width between 30 and 40 G, thus providing a facile characterization of the three ET/Cu(CF{sub 3}){sub 4}{sup {minus}} phases based on their ESR peak-to-peak line widths. X-ray studies on the semiconductor indicated a similar unit cell compared to the previously reported {alpha}-(ET){sub 2}Ag(CF{sub 3}){sub 4} phase. Superconducting K{sub L}- and K{sub H{sup {minus}}}(ET){sub 2}Cu(CF{sub 3}){sub 4}(TCE) crystals lost their cocrystallized solvent, TCE, at 340 and 380 K, respectively, and were converted to semiconducting (ET){sub 2}Cu(CF{sub 3}){sub 4}, indicating the close relationship among these three compounds.