This work was supported at SUNY-Binghamton by Grant No. DMR-9623221 from the Division of Materials Research at the National Science Foundation, at Argonne National Labs by Grant No. W-31-109-ENG-38 from the Division of Materials Research, Office of Basic Energy Sciences at the U.S. Department of Energy, and at Portland State University by NSF (CHE-9632815) and the Petroleum Research Fund (ACS-PRF No. 31099-AC1).
Physical Review B
Organic superconductors, Transition metals -- Optical properties
We report the polarized infrared and optical reflectance of β″-(ET)₂SF₅CH₂CF₂SO₃ as a function of temperature. This fully organic superconductor displays weakly metallic behavior over the entire temperature range of our investigation. The electronic properties present several unusual features including the lack of a conventional free carrier (Drude) response at low temperature, infrared localization phenomena, and an unexpected temperature dependence of the oscillator strength. Similar behavior is observed in other β and β″ superconductors above Tc, suggesting that this class of compounds is very close to a metal→insulator transition where electronic correlations are important and the Drude response carries very little spectral weight. Vibronic features increase in intensity with decreasing temperature in the infrared, as expected. The temperature dependence of key anion vibrational modes are discussed in terms of intermolecular hydrogen bonding within the anion pocket. [S0163-1829(99)04330-1]
Dong, J., Musfeldt, J. L., Schlueter, J. A., Williams, J. M., Nixon, P. G., Winter, R. W. and Gard, G. L. (1999). Optical properties of β″-(ET)₂SF₅CH₂CF₂SO₃: A layered molecular superconductor with large discrete counterions. Physical Review B, 60, 4342.