Infrared and Raman Study of the Charge-Ordered State in the Vicinity of the Superconducting State in the Organic Conductor β-(meso-DMBEDT-TTF)_2PF_6(Condensed matter: electronic structure and electric, magnetic, and optical properties)

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We present spectroscopic evidence for charge ordering in β-(meso-DMBEDT-TTF)_2 PF_6 below 〜70K. Its infrared and Raman spectra change abruptly at 〜70K. The amplitude of the charge order was estimated to be 0.5 from the splitting of the infrared-active C=C stretching mode. The coexistence of both high-temperature and low-temperature signals was observed in a narrow temperature range (〜4K) near the phase transition temperature. The pressure and temperature phase diagram was obtained in the vicinity of the superconducting phase. The checkerboard-type charge-order phase is not directly adjacent to the superconducting phase, but the superconducting phase is adjacent to the insulating phase where the short-range ordered domain of charge order is growing. The coexistent region expands significantly when hydrostatic pressure is applied. In the coexistent region, the crystal is inhomogeneous not just on a macroscopic scale, but also on a mesoscopic scale.
社団法人日本物理学会の論文
2008-02-15