- 1 - 有機導電体における分子自由度 ・分子性導体の歴史 ・ (EDO-TTF) 2 PF 6 の多重不安定性 超高速・高効率光誘起相転移・分子の化学修飾と錯体の物性変化 低温物質科学研究センター 矢持 秀起

- 2 - Molecular Conductor ― Summarized History 1954 Organic Semiconductor1960s 1D Organic Metals1980s: Organic Superconductors Q1D Superconductors max. T c = 1.4 K (AP) 2D Superconductors max. T c = 12.3 K (AP) Increment of Dimensionality 1990s: 3D Molecular Superconductors max. T c = 33 K (AP)

- 3 - TTFTCNQ - The First Organic Metal 38 K 54 K Peierls gap TTFTCNQ In TTF chain in TCNQ chain Semiconductor Metal

- 4 - Increasing the Dimensionality Increment of side-by-side intermolecular interaction TTF BEDT-TTF (ET) Number of Atoms TMTSF Atom Size

- 5 - TMTSF Superconductors

- 6 - & much more at present BEDT-TTF Superconductors

dimensional Superconductors Max T c = 33 K (RbCs 2 C 60 ) Alkali metals are in the interstitial sites among C 60 's.

s: Organic Superconductors Q1D Superconductors max. T c = 1.4 K (AP) 2D Superconductors max. T c = 12.3 K (AP) Summarized History 1954 Organic Semiconductor1960s 1D Organic Metals Increment of Dimensionality 1990s: 3D Molecular Superconductors max. T c = 33 K (AP) Molecular Degree of Freedom Lattice point  Simply a point  Size  Shape  Functionality

- 9 - BEDO-TTF(BO) Salt Self-assembling Packing Pattern 2D Layered Structure 3a+c vdW SS = 3.60 Å SO = 3.32 Å Side-by-side Heteroatomic Contacts a+2c vdW HO = 2.72 Å Weak Hydrogen Bond Network  2D Electronic Structure Calculated Fermi Surface

Partial Suppression of Self-assembling Nature of BO Introduction of Bulky Substituent Removal of an EDO Group Flat Side Surface -OCH 2 CH 2 O-  Stable Metal NO PHASE TRANSITION obstruction

EDO-TTF Complexes No Metal No Self-assembling A. Ota, et al., Mol. Cryst. Liq. Cryst., 376, (2002) + TCNQ deriv.  + Inorg. Anions  Variety of Structure & Properties 2:1 ReO 4, GaCl 4  RT = 130, 54 Scm -1 Activated behaviors  250 K Different typed columns 5:3 BF 4  RT = 1 Scm -1 (Ea = 62 meV) 4:0.85:4(H 2 O) Sb 2 F 11  RT = 2 Scm -1 (Ea = 55 meV) Multimer & monomer A. Ota et al., J. Low Temp. Phys., 142 (3/4), 425 (2006) A. Ota et al., in “Multifunctional Conducting Molecular Materials”, eds. G. Saito et al., RSC Publishing, Cambridge, UK. (2007), pp At 2001 (w hen we started ), Synthesis of donor A few kinds of complexes No description of composition Conductivity: No description or  2  Scm  1

EDO-TTF — Preparation of PF 6 Complex A. Ota et al., J. Mater. Chem., 12, 2600 (2002)

Thermally Induced MI Transition of (EDO-TTF) 2 PF 6 T MI  280 K  jump: ca. 5 order Paramag.  Non-mag. First-order Transition

How Metal-Insulator Transitions Occur itinerant electrons Spin Density Counter Component On-site Coulomb (U) Neighbor-site Coulomb (V) CDW Anion Ordering (order- disorder) SDW Mott Charge Ordering Peierls New periodicity by Charge & Lattice Charge density Localization by Coulomb repulsion NO One Mechanism for One Transition

planar: 0.8º, 2.1º bent: 11.1º, 7.9º  1,  2 : 6.0º, 0.3º Distinct Molecular Deformation PF 6 Rotation Isotropic (EDO-TTF) 2 PF 6 — Above and Below T MI (280 K) Overlap Integral Uniform from Bond Length 0.5+ Molecular Deformation is regarded as the Origin to Mix Metal-Insulator Transition Mechanisms (Multi-instability). Alternate Peierls (Overlap Integral  10 3 ) 1+/0 Charge Ordering Uniaxial Order- Disorder

(EDO-TTF) 2 PF 6  Other Properties  Raman Spectra: 4.2 K  Coexistence of 0.9+, 0.1+ Donors O. Drozdova et al., Synthetic Metals, , (2003). Accurate Structure Analysis with MEM method: 285 K  +0.6(1) 260 K  F: +0.8(1), B: +0.2(1) S. Aoyagi et al., Angew. Chem. Int. Ed., 43 (28), (2004). Calorimetry: Transition Entropy  Unharmonicity of PF 6 Rotation in RT Phase K. Saito et al., Chem. Phys. Lett., 401 (1-3), (2005). Reflection Spectra: Significant Temperature Dependence O. Drozdova et al., Phys. Rev., B70 (7), (2004). Photo-induced Phase Transition: Ultra-fast Highly Efficient, ~ 0.1 ps, donors/photon M. Chollet et al., Science, 307, (2005). Uni-axial Strain: along c*  T MI  (> 60 K/4 kbar) M. Sakata et al., Synthetic Metals, 153 (1-3), (2005).

Photo-induced Phase Transition (PIPT) Completes in ca. 1.5 ps Probe PIPT to Highly Conducting Metastable State 1 photon / molecules M. Chollet et al., Science, 307, (2005) vibration: ca. 0.5 ps/cycle at 180 K Strong Electron-Lattice Interaction Pump 1.55 eV Time Delay

Our system 50 – 500 molecules 50 – 500 molecules within ca. 0.1 ps within ca. 0.1 ps one photon RbTCNQ (Ins. - Metal) < 10 molecules, ca. 0.1 ps TTF-Chloranil (Neutral - Ionic) 280-2,800 molecules,  1 ns PIPT — Comparison with other systems Ultra-fast & Highly Efficient PIPT Controllable Initialization Development of Phase Transition  Dynamics of Non-equilibrium State  Dynamics of Non-equilibrium State

Optical Conductivity (10 3  -1 cm)  R/R LT phase (180 K) HT phase (290 K) Wide Range Optical Conductivity Spectra Simulated (simple multilayer model) K. Onda, S. Ogihara, K. Yonemitsu, N. Maeshima, T. Ishikawa, Y. Okimoto, X.F. Shao, Y. Nakano, H. Yamochi, G. Saito, S. Koshihara, Phys. Rev. Lett., 101(6), (2008) 0.1 ps after pump one peak at low energy Theoretical Calculation H : t, U, V,  (e-ph coupling  anion potential modulation) time dependent model PIPT state: (1010) Charge Disp.  RT Metallic (½ ½ ½ ½) Phase Lattice potential: fluctuated in this time scale PI Metastable State  RT Metallic Phase =?=? : (0110)

After (EDO-TTF) 2 PF 6  Isotope Effect Isotope substitution  Lattice (Molecular) Vibrations Electron-Phonon (Electron- Molecular Vibration) Coupling (EDO-TTF- d x ) 2 AsF 6  Modulation of  -system (conduction path) vibrations  For PF 6 & AsF 6 complexes d 0  d 2  T MI  3 K

T MI by Magnetic Susceptibility Size T MI (K)Δ T MI (K) PF AsF SbF T MI ↓ T MI ↑ Isostructural (EDO-TTF) 2 XF 6 (X = P, As Sb) After (EDO-TTF) 2 PF 6  Anion Size Effect スライド内容 一部削除 ここで観測された、転移温度とヒステリシ ス幅の陰イオン依存性については、現在、 その詳細を解析中です。

Molecular Design Based on EDO-TTF Distinct Molecular Deformation Multi-instability of Itinerant Electrons EDO-TTF having Small Sized Substituent To Find Further Peculiar Systems Similar  -electron system Similar Molecular Size Lower Symmetry cf. 17 % yield: A. Miyazaki et al., (2001)

Complexes AnionD : A  rt (S cm -1 ) Compressed Pellets BF 4 2 : 126 (Metal) ClO 4 2 : 124 (Metal) PF 6 2 : 1 3 (Semi.) AsF 6 2 : 115 (MI at 240 K) SbF 6 2 : 1 6 (MI at 250 K) HCTMM4 : 1 6 (Semi.) X.F. Shao et al., J. Mater. Chem., 18, (2008) 2:1 PF 6  rt (S cm -1 ) Black powder 3 (Semi.) Dark green plates29 (MI at 200 K) Black plates 0.07  4 (Semi.-Semi. at 303 K)

c-axis projection Crystal Structure of (MeEDO-TTF) 2 X (X = BF 4, ClO 4 ) Orthorhombic Cmcm a = (2) Å b = (1) c = 6.969(1) V = (4) Å 3 Z = 4 R = 5.7 % (I o > 2  (I o )) GooF = Metal down to 10 K Donor: Head-to-Head (parallel) Anion: Disordered a-axis projection t = 11.7, p = 8.4, s = -5.1  D Fermi Surface with weak intermol. interactions For X = BF 4

(MeEDO-TTF) 2 PF 6 : Semiconductor-Semiconductor Black Plate H-phase isostructural with metallic BF 4 & ClO 4  = 0º   4º H-phase L-phase Nearly Localized Charge-order Definitive Charge-order Area of Conducting Layer (Å 2 ) StableBF 4 ClO 4 PF 6 Semi- metal conductor V/t

有機導電体における分子自由度 ・格子点 ・格子点  点 形状・大きさ・機能性形状変化が可能・新たな機能性物質多重不安定性外場敏感相転移物質光誘起相転移物質 → 開始時刻の制御 → 開始時刻の制御 → 非平衡状態の研究 → 非平衡状態の研究

低温物質科学研究センター Research Center for Low Temperature and Materials Sciences 分子性材料開拓・解析研究分野 Division of Molecular Materials Science