ISCOM2009International symposium on crystalline organic
metals, superconductors, ferromagnets
announcement
At Niseko in Hokkaido, Japan
On Sep. 12 – 17, 2009 (Sep. 12; get-together)
New Aspects of Neutral-Ionic Transition (NIT)Revealed by Magnetic Resonance
ECRYS2008 , Cargese, Corsica, Aug. 25-30, 2008
K. Kanoda, Applied Physics, University of Tokyo
0. Introduction to NIT
1. Observation of quantum critical fluctuations in NIT
2. Separation of charge transfer and dimerization
F. Iwase ( present; IMS), K. Miyagawa
Y. Tokura, H. Okamoto
S. Horiuchi
K. Murata
Collaborators Univ. Tokyo
AIST
Outline
Osaka City Univ.
Neutral-Ionic transition (NIT)
QCl4TTF
TTF-QCl4
paraelectric
ferroelectric
Neutral
Ionic
Torrance et al., PRL. (1981)
Charge transfer -- Redox
Dimerization --symmetry breaking
TemperaturePressure
Charge-lattice-coupled phenomenaSpin-Peierls
NIT phase diagramLemee-Cailleau et al. PRL 79, 1690 (1997)
Okamoto et al.
Neutral phase
Ionic phase
1st-order transition of simultaneous CT and dimerization
TTF-QCl4
NIT in DMTTF-QCl4 –continuous and quantum
DMTTF QCl4
QCl4
DMTTF-2,6-QBr2Cl2
QBr4
Horiuchi et al., J. Am. Chem. Soc., 123, 665 (2001).
Chemical pressure
Physical pressure
by Horiuchi, Tokura
Neutral
Ionic
Continuous transition
Nuclear quadrupole resonance (NQR) probes the charge state and symmetry of the lattice
rf pulse
Qh2/3m
2/1m
1I I=3/2
31
2
22
Q
qQe
Resonance frequencyzzVq e
zzyyxx VVV
Electric field gradient (EFG)
Charge transfer Dimerization
nucleus
Cl or Br nuclei
e - e -
Q Q
line shift line splitting
Cl or Br nuclei
NQR
Ionic
Neutral
Spectral splitting
QCl4
Spectral shift
Symmetry breaking (dimerization)
Charge transfer
Neutral
Ionic
TTF-QCl4 Cl-NQR
J. Gallier et al., Phys. Rev. B, 47, 11688 (1993).
Iwase et al., JPSJ (2007)
Spin-lattice relaxation rate 1/T1
DMTTF-QBr4 Br NQR
011 2coth2 TTTT
BA
T0 : Curie-Weiss temperatureT1 : characteristic crossover temperature dividing the quantum and classical region
Barrett formula:
DMTTF-QCl4 35Cl NQR
cs PPPP split)0,(
Pc(20K)=1.41 kbar
Pc(5K)=1.32 kbar
=0.55
=0.55
20 K
5 K
dimerization
mean-field behaviorR. Morf et al., PRB 16462 (1977).
Pressure-induced NIT at low TNQR spectra at 5K
Pressure-induced NIT; continuous and quantum
QBr4 molecule
79Br NQR
Quantum critical fluctuations
Spins are hidden all the way across the transition
Extended phase diagram of TTF-QCl4
Dimer liquid
Dimer crystal
Long-range order
Short-range order
Charged spin soliton
polarization