Spectroscopic characterization of (BEDT-TTF)2[Pt(S2C4O2)2] charge density wave ground state
Abstract
We report a detailed spectroscopic characterization of the charge transfer (CT) complex between bis(ethylendithio)tetrathiafulvalene (BEDT-TTF) and bis(dithiosquarate)platinate(II), (BEDT-TTF)
2
[Pt(S
2
C
4
O
2
)
2
]. In this complex BEDT-TTF dimers are separated by the [Pt(S2C4O2)2]
2–
anions, forming a quasi-one-dimensional stack. We show that the stack structure is stabilized by CT between BEDT-TTF dimers and between BEDT-TTF and [Pt(S
2
C
4
O
2
)
2
]. Two CT transitions, polarized along the stack axis, are identified in the optical spectra. Furthermore, the average charge on the molecules is not a multiple integer, and the amplitude of the intrinsic ground state charge density wave (CDW) can be represented as: …[Pt(S
2
C
4
O
2
)
2
]
1.8–
BEDT-TTF
0.9+
BEDT-TTF
0.9+
[Pt(S
2
C
4
O
2
)
2
]
1.8–
… The optical spectra polarized along the (BEDT-TTF)
2
[Pt(S
2
C
4
O
2
)
2
] stack are well reproduced by a semiempirical model which takes into account the coupling of BEDT-TTF molecular vibrations with the CT electrons (e-mv coupling). Under pressure, (BEDT-TTF)
2
[Pt(S
2
C
4
O
2
)
2
] undergoes two distinct phase transitions in the ranges 1-1.6 and 2.2-2.5 GPa, the first involving a stack distortion.
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