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)

NQR spectra

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

Two messages on NIT

• Critical fluctuations of N-I transition at low temperatures.

They are likely quantum.

• Charge-lattice separation in low-energy scale in a wide P-T range.

Dimer liquid

Dimer crystal