Quantum Phase Transition in Organic Charge-Transfer Complexes
Sachio Horiuchi,1*
Yoichi Okimoto,1
Reiji Kumai,1
Yoshinori Tokura123
A phase transition in an organic charge-transfer
complex, which originates from the neutral-ionic valence instability,
can be tuned toward zero kelvin with use of external pressure or
chemical modification as a control parameter. The phase diagram and
observed dielectric behaviors are typical of quantum paraelectricity,
yet this zero-kelvin transition point namely, the quantum critical point, accompanies large quantum fluctuation of the molecular charge,
as demonstrated by the molecular vibrational mode spectra. The result
indicates that the 
-electron transfer between donor and acceptor
molecules is coupled with the zero-point lattice dynamics around the
quantum critical point.
1 Correlated Electron Research Center (CERC),
National Institute of Advanced Industrial Science and Technology
(AIST), Tsukuba, 305-8562, Japan.
2 Spin
Superstructure Project (SSS), ERATO, Japan Science and Technology
Corporation (JST), c/o National Institute of Advanced Industrial
Science and Technology, Tsukuba, 305-8562, Japan.
3 Department of Applied Physics, University of
Tokyo, Tokyo 113-8656, Japan.
*
To whom correspondence should be addressed. E-mail:
s-horiuchi{at}aist.go.jp
