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Hong Kong Forum of Condensed Matter Physics: Electronic Properties of Molecular Solids

Explore past, present, and future advancements in electronic properties of molecular solids at the forum. Topics include molecular metals, insulating states, carrier doping, Peierls transition, and more. Learn about strong correlation effects, impurity pinning, and potential for high-Tc superconductivity. Discover molecular conducting crystals, charge transfer salts, and theoretical studies on friction processes in magnetic domains. Join us at the Univ. of Hong Kong from Dec 18-20, 2006.

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Hong Kong Forum of Condensed Matter Physics: Electronic Properties of Molecular Solids

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  1. Hong Kong Forum of Condensed Matter Physicsー Past, Present and Future　－December 18-20, 2006 @ Univ. of Hong Kong Electronic Properties of Molecular Solids H. FukuyamaDepartment of Applied Physics, Faculty of Science, Tokyo University of Science

  2. OUTLINE 1) Molecular metals for the past 30 years 2) Origin of insulating states 3) Carrier doping by charge transfer; from perylene:Br to A2B, eventually single-component metals. Molecular solids: a showcase of strong correlation 4) Non-crystalline molecular materials Possible carrier doping into DNA 4) Future Electronic properties of molecular assemblies Electronic properties of interfaces and contacts HF: JPSJ 75(2006)051001

  3. Molecular Conducting Crystals

  4. Peierls Transition TTF-TCNQ CDW: Combined degrees of freedom of electrons and lattice distortions Collective mode: Phason Lee-Rice -Anderson(1974) "superconducting fluctuations"

  5. Impurity Pinning 2)weak pinning : ε<< 1 fluctuations of potential => collective effects Cf. Larkin-Ovchinikov: vortices Phase Hamiltonian : HF(1976) Parameter : ε=V0/nivF HF-Lee (1978) １）strong pinning : ε>> 1 => In 3d : Lee-Rice

  6. “ Fukuyama - Lee - Rice ” (1987.9.4)

  7. Theory of Friction "Theoretical Studies of Friction: One-dimensional Clean Surface" Matsukawa-HF, PRB (1994) “ Current driven magnetic domain wall motion” Gen Tatara et al., J. Phys. Soc. Jpn (2006) “Friction processes of magnetic domain with internal degree of freedom” Frenkel-Kontrova model Velocity-dependent frictional constant

  8. Molecular Conducting Crystals

  9. A2B Charge Transfer (CT) Salts : A+1/2 B-1 Cf. A1-xBx : x->0 Carrier Doping into Band Insulators Si:P, Si:B Perylene:Br

  10. semiconductors Anderson localization Si Insulator Metal Band insulator + impurities => Small amount of carriers => Easy to control => Switchable FET Carrier Doping into Insulators＝> Metallic Conduction 20

  11. , Superconductivity in B-doped Diamonds and even in Silicon ! E. A. Ekimov et al., Nature 428, 542 (2004) Strong Disorder Takano et al. (2005) Ioffe-Regel criterion for coherent Bloch-like transport is violated. No coherent band structures Superconductivity without Fermi surface “Poor Metals” Covalent bonds appear at Fermi energy due to doping. => High Tc !! Shirakawa-Horiuchi-Ohta-HF, JPSJ 76(2007) #1

  12. Typical Molecular Conductors A2B

  13. Tight - binding approximation based on molecular orbitals works quite well! Validity of Extended Huckel Approx. for one-particle band structures 1980~ H.&A.Kobayashi, T.Mori, R.Kato,-- => Even to designing !

  14. Systematic Studies on the Electronic Properties of Molecular Solids Effects of mutual interactions Extended Hubbard Model H = Σti,i+1(cis† ci+1s + h.c. ) + ΣUni↓ni↑ + ΣVi,i+1nini+1 ti,i+1: takes full account of molecular orbitals, esp. anisotropy Mean-field approx. very suited for global understanding. (High energy properties) More elaborate studies if necessary , e.g. based on the Heisenberg spin model. (Low energy properties) H.Seo, C.Hotta, HF, Chemical Reviews 104, 5005(2004)

  15. • case 1 : strong dimerization t1 >> t2 + on-site Coulomb interaction U • case 2 : intersite Coulomb interaction V S=1/2 per dimer S=1/2 on every other site dimer Mott-Hubbard insulator (uniform charge density) Wigner Crystal type Charge Ordering A2B materials (A0.5+)2B– or (A0.5 –)2B+ → A : ¼-filled (if all A equivalent) two limiting cases for insulator due to Coulomb interaction in 1/4-filling

  16. demonstration : high pressure study on TMTTF2PF6 Metal-Insulator transition : nesting of Fermi surface H C Se Se CH 3 3 Se Se H C CH 3 3 54kbar 8kbar 66kbar 52kbar 18kbar 47kbar Adachi-Ojima-Kato-Kobayashi-Miyazaki-Tokumoto-Kobayashi ‘00 “Jerome’s phase diagram” Jerome et al. : ‘80s ~ TMTSF2X, TMTTF2X “1d ” molecule TMTSF TMTTF : Se → S crystal structure PF6 - TMTSF

  17. Emery-Bruisma-Barisic ’86 : “Mott-Hubbard insulator” Nakamura-Nobutoki-Kobayashi-Takahashi-Saito ’95 : “ antiferromagnetic spin structure by 1H-NMR “ ⇒ Charge Order ! mean-field calculation including intersite Coulomb interaction V Seo-HF JPSJ ‘97 Charge Order in TMTTF2X ‐1‐

  18. Charge Order in TMTTF2X ‐2‐ dielectric constant 13C-NMR TMTTF2AsF6 AsF6 SbF6 PF6 Monceau-Nad-Brazovskii PRL ‘01 Ferroelectricity !! Chow et al PRL ’00 Zamborsky et al PRB ‘02

  19. “Jerome’s phase diagram” NEW phase diagram

  20. S S S S S S S S quasi-2-D crystal structure variety in in-plane (2d) lattice structures : polytypes a, b, q, k, l, … mean-field calculations on Hubbard models → systematic understanding of ground states ET Kino-Fukuyama JPSJ ’95,’96 “ 2d ” ET=BEDT-TTF :

  21. Degree of anisotropy of triangular lattice C.Hotta, JPSJ 72, 840(2003); H.Seo,C.Hotta,HF: Chemical Reviews

  22. ET2X:κ and λ Types Strongly Dimerized => Dimer Mott Systems Kanoda Anisotropic Triangular Lattice Kino-HF: J.Phys.Soc.Jpn 65(1996)2158

  23. k-(ET)2X ~ 2D triangular lattice Dimer ET forms triangle H. Kino & H. Fukuyama, JPSJ (1995). ET+0.5 b1 >> b2, p, q t = (p| + |q|)/2 t' = b2/2 X-1 conducting ET layer Insulating anion layer t’/t : 0.5 ~ 1.0 Large frustration!? Courtesy of Kanoda

  24. anisotropic triangular lattice is modeled to In-plane structure layered structure ET Conducting layer Insulating layer S S X S S S S S S k-(ET)2X ~ 2D triangular lattice with half-filled band Kino-HF,JPSJ X U/t t’/t Cu2(CN)3 8.20 1.06 Cu[N(CN)2]Cl 7.58 0.74 Cu[N(CN)2]Br 7.20 0.68 Cu(NCS)2 6.98 0.86 I3 6.48 0.58 Mott insulator Mott insulator U/W Mott insulator SC SC SC 1/2 filled 0 1 2 Hole number / dimer

  25. 1H-NMR spectra k-(ET)2Cu2(CN)3 (t’/t =1.05) k-(ET)2Cu[N(CN)2]Cl (t’/t =0.74) H (2.2 T)  2D plane H (3.7 T)  2D plane No splitting! No broadening moment < 0.01mB if any FFT of Solid echo signal Antiferromagnetic order below 27 K (0.45mB) No magnetic order!spin liquid state

  26. Degree of anisotropy of triangular lattice C.Hotta, JPSJ 72, 840(2003); H.Seo,C.Hotta,HF: Chemical Reviews

  27. ET2X with no/weak dimerization q-type a-type a-ET2I3 q-ET2RbZn(SCN)4 Bender et al. ’84 N.Tajima et al. ‘00 Rothaemel et al. ’86 H.Mori, S.Tanaka, T.Mori ‘98

  28. ET2X with no/weak dimerization ‐charge order‐ Seo (2000) a-ET2I3 q-ET2RbZn(SCN)4 1D Heisenberg chain, uniform J ~ 450K (experiments : J ~ 160K) 1D alternating Heisenberg chain J1 ~ 1000K, J2 ~ 200K (experiments : J1 ~ 500K, J2 ~ 100K) => Singlet ground state Cf. TMTCF2X: Seo, Monceau , Brown,

  29. "Viscous" electron liquid q-type a-ET2I3 q-ET2RbZn(SCN)4 H.Mori, S.Tanaka, T.Mori ‘98 a-type Above (or Near) CO, resistivity is large and almost temperature-independent with low energy dynamics. =>Viscous electron liquid. By NMR: Takahashi, Kanoda Frustrations between different spatial pattern of CO H.Mori(1998) Bender et al. ’84 N.Tajima et al. ‘00

  30. Tajima et al., JPSJ 71(2002)1832. “ Zero-gap semiconductor (ZGS) ” K. Kajita et al.,JPSJ 61(1992) 23. SC in the presence of Charge Ordering => “self-doped Heisenberg chain” A. Kobayashi

  31. “Neutrino” in Solids S. Kobayashi, A. Kobayashi and Y. Suzumura, cond-mat/0601068

  32. New Particles in α-ET2I3 H = v( kxσx + kyσy ) for graphene Weyl eq. for neutrino H = k・Vρσρforα-ET2I3 σ0 = 1, σαPauli Matrix A. Kobayashi Hall effects and orbital magnetism persistent current vs. dissipative current Inter-band effects of magnetic field

  33. Single Component Molecular Metals A.Kobayashi-Tanaka-H.Kobayashi(2001)

  34. Single component mol metal“Molecules behave like alkaline metal ions”

  35. b* a* c* c* C* [Ni(tmdt)2] b* S. Ishibashi a* ・The observation of dHvA oscillation (510 Tesla ~ 10% of the 1st Brillouin zone) 1st principles density functional calculation ......E. Canadell et al. H. Tanaka, M. Tokumoto (AIST), J. Brooks(NHMFL/FSU)

  36. Π-d Crystals - Metals in the sea of π-electrons - * DCNQI2Cu : Valence fluctuations *λ-BETS2FeCl4magnetic field induced superconductivity (Kobayashi, Uji,-) *(EDT-TTFVO)2FeBr4 ferromagnetic semiconductors (Sugimoto,Noguchi,-) *ET3[MnCr(C2O4)3] ferromagnetic metals (Coronado) *TTP[Fe(Pc)(CN)2]2 charge ordering in dense Kondo (Inabe,Tajima; Hotta,Ogata,HF)

  37. Phthalocyanine, MPc Craciun et al.(2005) M= Fe, Co, Ni, Cu, Zn, Mg Cf. Cu(F8Pc),Cu(F16Pc): N. Sato

  38. So far, crystals of molecules. How about non-crystalline materials? • Myoglobin • DNA Shin-Tarada-Tokushima-Miyajima-Taguchi (ISSP-RIKEN)

  39. porphyrin ヒスチジン Local structure around Heme in proteins Histidine Courtesy of Shin

  40. S=2 S=5/2 (H2O) (deoxy) S=0 S=1/2 (CN,N3) (O2,CO) 4 possible electronic states of Fe in Myoglobin By changing the spin and electron valency, Myoglobin catches and releases the various gases Fe High spin Histidine Fe2+ Fe3+ O2 Fe Low spin Histidine Courtesy of Shin

  41. DOS of valence states Alowed transition Transition elements2p,3p→　3drare earth elements　･･3d,4d　→ 4flight element　･･･ 1s→ 2p O2p, N2p, C2p DOS hn hn’ hn hn’ Fe 3d DOS Fe dd励起 SXES Shin (ISSP) SP-BL17 非占有 EF 価電子 占有 内殻

  42. O N N Fe N N N Theory（Cluster model） Hamiltonian Ligand 2p Fe 3d Fe 2p Fe 3d – Ligand 2p hybridization Fe 3d Coulomb interaction Fe 2p-3d core-hole potential

  43. ＤＮＡ 提供：マウロ（真宇呂）・ボエロ氏

  44. Electrical conductivity:wide variation in experimental results I-V Curve dG-dC 10-4Wcm(600nm-900nm),T=RT Fink et al., Nature 398, 407(1999) 10.4nm, T=100K-RT Porath et al., Nature 403, 635(2000) Low resistance High resistance Why ?

  45. any experiments in condensed matter should pay attention to 1) sample characterization 2) how to measure Issues: 1) Are carriers doped ? 2) How about contacts ?

  46. “Contact problem” Cf.井上

  47. J.Phys.Soc.Jpn73(04)#8 p.2089 A Possible Origin of Carrier Doping into DNA Hiori Kino (NIMS) Masaru Tateno (TIT & AIST) Boero (Tsukuba Univ.) Mauro Takahisa Ohno (NIMS) Kiyoyuki Terakura (Hokkaido Univ.& AIST) Hidetoshi Fukuyama (Tohoku Univ.) -Addressing to Possible Carrier Doping -

  48. hydrated Mg anhydrous Mg cations cation (c) (c’) LUMO (GGA/PBE gap~0.7eV) LUMO@G LUMO (b) 7.6 eV (b) Mg+ HOMO Mg2+ Sz=0 Sz=1 SOMO (c’) (a) (a) Unoccupied state (b) B Occupied state (c’) (c) (b) (a) G G Calc. UHF/6-31G(d) Electronic structure of DNA hydrate v.s. anhydrous Mg PO4-1 C [(dG)2Mg(H2O)n]+ PO4-1 Mg2+ G

  49. poly(dG)-poly(dC) with anhydrous Mg Electronic structure of dry DNA [(dG)2-Mg2+] LUMO impurity m hole G HOMO m HOMO(G) DOS(dopant) DOS(host) Similar to doped semiconductors for divalent cations(cf. Si-P) ＝＞metallic DNA ? M+1: 　Ｓ＝1/2 Not for monovalent cations

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