20 K CRYSTAL-STRUCTURE, ELECTRICAL-TRANSPORT, ELECTRONIC BAND-STRUCTURE, SCANNING-TUNNELING-MICROSCOPY AND PRESSURE-RF IMPEDANCE STUDIES ON THE ORGANIC CONDUCTING SALT KAPPA-(BEDT-TSF)(2)CU[N(CN)(2)]BR

The electrochemical synthesis of kappa-(BEDT-TSF)(2)Cu[N(CN)(2)]Br, which is virtually isostructural (Pnma) with the 12.5 K ambient pressure superconductor kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br, has been systematically investigated. The electrical resistivity of kappa-(BEDT-TSF)(2)Cu[N(CN)(2)]Br was measured in the a [rho(300) = 2(1) x 10(-2) Omega cm] and b [rho(300) = 1.7(0.7) x 10(1) Omega cm] crystallographic directions. The resistivity decreased monotonically from 300 to 4 K following a T-2 relationship, but a superconducting state was never achieved. Tight-binding band calculations showed that the Fermi surface of kappa-(BEDT-TSF)(2)Cu[N(CN)(2)]Br is indistinguishable from the BEDT-TTF analogue. STM images were obtained of both the radical cation and the polymeric anion layers. The images were in agreement with partial electron density plots. A 20 K X-ray structure of K-(BEDT-TSF)(2)Cu[N(CN)(2)]Br was obtained and is discussed in detail. One of the BEDT-TSF ethylenedithio groups was still disordered at 20 K; this may have been responsible for the failure to observe superconductivity. Isotropic pressures up to 5 kbar did not induce superconductivity.