Infrared conductivity and electron--molecular-vibration coupling in the organic superconductor di(bis(ethylenedithio)tetrathiafulvalene) bis(isothiocyanato)cuprate(I), kappa-(BEDT-TTF)/sub 2/ (Cu(NCS)/sub 2/): Protonated and deuterated salts

Journal Article · Thu Jun 01 04:00:00 EDT 1989 · Phys. Rev. B: Condens. Matter; (United States)

DOI:https://doi.org/10.1103/PhysRevB.39.11387· OSTI ID:6035759

Sugano, T; Hayashi, H; Kinoshita, M; Nishikida, K

Polarized reflectance spectra of the organic superconductors protonated and deuterated kappa-(BEDT-TTF)/sub 2/(Cu(NCS)/sub 2/) (H and D salts) (BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene) were measured over the range from 500 to 28 000 cm/sup /minus/1/ at room temperature with light polarizations parallel to the crystallographic /ital b/ and /ital c/ axes which lie on the two-dimensional conducting plane. Polarized reflectance spectra of the organic superconductor ..beta..-(BEDT-TTF)/sub 2/I/sub 3/ and the organic metal ..beta..''-(BEDT-TTF)/sub 2/AuBr/sub 2/ were also measured in order to discuss the influence of different molecular arrangements and hydrogen-anion contacts on the electronic and vibrational properties of these salts. Frequency-dependent conductivities were calculated by a Kramers-Kronig transformation. By comparison of the infrared conductivity spectra of the H and D salts, the vibrational transitions induced by electron--molecular-vibration (EMV) coupling were clearly distinguished from the carbon-hydrogen bending modes of the BEDT-TTF moiety. A Drude-Lorentz dielectric function was used to evaluate the optical transport parameters and an excitation frequency of the charge-transfer (CT) band superimposed on a plasma-edge-like dispersion which was observed for each compound. The EMV-coupling energies are semiquantitatively estimated to be ca. 70 meV for both the H and D salts from the frequencies of the EMV coupling transition and the CT band in terms of the dimer charge-oscillation model. By use of the coupling energy, various parameters describing the superconducting state were evaluated and discussed on the basis of the BCS theory in a weak-coupling limit. Finally, the magnitudes of hydrogen-anion interaction were estimated from the frequency shifts of the C-H bending modes of the BEDT-TTF moiety.

• Research Organization: The Institute for Solid State Physics, The University of Tokyo, Roppongi, Minato-ku, Tokyo 106, Japan(JP); Perkin-Elmer Japan, Kitasaiwai, Nishi-ku, Yokohama 220, Japan
• OSTI ID: 6035759
• Journal Information: Phys. Rev. B: Condens. Matter; (United States), Journal Name: Phys. Rev. B: Condens. Matter; (United States) Vol. 39:16; ISSN PRBMD
• Country of Publication: United States
• Language: English

Related Subjects

656100* -- Condensed Matter Physics-- Superconductivity
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
BEDT-TTF
COLLISIONS
COPPER COMPOUNDS
CUPRATES
ELECTRON COLLISIONS
ELECTRON-MOLECULE COLLISIONS
ELECTRON-PHONON COUPLING
HETEROCYCLIC COMPOUNDS
INFRARED SPECTRA
LATTICE VIBRATIONS
LIGHT SCATTERING
MEDIUM TEMPERATURE
MOLECULE COLLISIONS
ORGANIC COMPOUNDS
ORGANIC SULFUR COMPOUNDS
OXYGEN COMPOUNDS
POLARIZATION
REFLECTION
SALTS
SCATTERING
SPECTRA
SUPERCONDUCTORS
TRANSITION ELEMENT COMPOUNDS