Hong Kong Forum of Condensed Matter Physics Past, Present and Future December 18-20, 2006 Univ. of Hong Kong,Electronic Properties of Molecular Solids H. Fukuyama Department of Applied Physics, Faculty of Science, Tokyo University of Science,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 materialsPossible carrier doping into DNA 4) FutureElectronic properties of molecular assembliesElectronic properties of interfaces and contactsHF: JPSJ 75(2006)051001,Molecular Conducting Crystals,Peierls Transition,TTF-TCNQ,“superconducting fluctuations“,CDW: Combined degrees of freedom of electrons and lattice distortionsCollective mode: PhasonLee-Rice -Anderson(1974),Impurity Pinning,Phase Hamiltonian : HF(1976),= In 3d : Lee-Rice,2)weak pinning : collective effects Cf. Larkin-Ovchinikov: vortices,Parameter : =V0/nivF HF-Lee (1978),）strong pinning : 1,“ Fukuyama - Lee - Rice ” (1987.9.4),Theory of Friction,“Theoretical Studies of Friction:One-dimensional Clean Surface“Matsukawa-HF, PRB (1994),Frenkel-Kontrova model,“ Current driven magnetic domain wall motion”Gen Tatara et al., J. Phys. Soc. Jpn (2006),“Friction processes of magnetic domainwith internal degree of freedom”,Velocity-dependent frictional constant,Molecular Conducting Crystals,A2BCharge Transfer (CT) Salts : A+1/2 B-1Cf. A1-xBx : x-0Carrier Doping into Band InsulatorsSi:P, Si:BPerylene:Br,Carrier Doping into Insulators Metallic Conduction,Si,semiconductors,20,Band insulator + impurities = Small amount of carriers = Easy to control = Switchable,Anderson localization,FET,Insulator,Metal,Superconductivity in B-doped Diamonds and even in Silicon !,Strong Disorder,Ioffe-Regel criterion for coherent Bloch-like transport is violated.,Takano et al. (2005),Superconductivity without Fermi surface“Poor Metals”,No coherent band structures,E. A. Ekimov et al., Nature 428, 542 (2004),Covalent bonds appear at Fermi energy due to doping. = High Tc !Shirakawa-Horiuchi-Ohta-HF, JPSJ 76(2007) #1,Typical Molecular Conductors A2B,Tight - binding approximation based on molecular orbitals works quite well!Validity of Extended Huckel Approx.for one-particle band structures1980 H.&A.Kobayashi, T.Mori, R.Kato,-= Even to designing !,Systematic Studies on the Electronic Properties of Molecular Solids,Effects of mutual interactionsExtended Hubbard ModelH = ti,i+1 ( cis ci+1s + h.c. ) + U nini + Vi,i+1 ni ni+1 ti,i+1 : takes full account of molecular orbitals, esp. anisotropyMean-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),A2B materials,(A0.5+)2B or (A0.5 )2B+ A : -filled (if all A equivalent),two limiting cases for insulator due to Coulomb interaction in 1/4-filling,TMTSF2X, TMTTF2X,PF6 -,TMTSF,TMTSF,molecule,crystal structure,“Jeromes phase diagram”,Jerome et al. : 80s ,TMTTF : Se S,“1d ”,Charge Order in TMTTF2X 1, Charge Order !,Charge Order in TMTTF2X 2,13C-NMR,dielectric constant,Ferroelectricity !,Chow et al PRL 00 Zamborsky et al PRB 02,Monceau-Nad-Brazovskii PRL 01,TMTTF2AsF6,PF6,AsF6,SbF6,“Jeromes phase diagram”,NEW phase diagram,ET=BEDT-TTF :,“ 2d ”,C.Hotta, JPSJ 72, 840(2003); H.Seo,C.Hotta,HF: Chemical Reviews,Degree of anisotropy oftriangular lattice,ET2X: and Types,Strongly Dimerized= Dimer Mott Systems,Kanoda,Anisotropic Triangular Lattice Kino-HF: J.Phys.Soc.Jpn 65(1996)2158,k-(ET)2X 2D triangular lattice,Insulating anion layer,conducting ET layer,ET+0.5,t = (p| + |q|)/2 t = b2/2,b1 b2, p, q,Dimer ET forms triangle,H. Kino & H. Fukuyama, JPSJ (1995).,X-1,t/t : 0.5 1.0,Large frustration!?,Courtesy of Kanoda,X U/t t/tCu2(CN)3 8.20 1.06 CuN(CN)2Cl 7.58 0.74CuN(CN)2Br 7.20 0.68Cu(NCS)2 6.98 0.86I3 6.48 0.58,U/W,Hole number / dimer,0,1,2,1/2 filled,Mott insulator,Mott insulator,Mott insulator,SC,SC,SC,k-(ET)2X 2D triangular lattice with half-filled band,Kino-HF,JPSJ,1H-NMR spectra,Antiferromagnetic order below 27 K (0.45mB),k-(ET)2Cu2(CN)3,k-(ET)2CuN(CN)2Cl,No splitting! No broadening,No magnetic order! spin liquid state,FFT of Solid echo signal,H (2.2 T) 2D plane,H (3.7 T) 2D plane,moment 0.01mB if any,(t/t =0.74),(t/t =1.05),C.Hotta, JPSJ 72, 840(2003); H.Seo,C.Hotta,HF: Chemical Reviews,Degree of anisotropy oftriangular lattice,ET2X with no/weak dimerization,q-type,a-type,H.Mori, S.Tanaka, T.Mori 98,Bender et al. 84 N.Tajima et al. 00,Rothaemel et al. 86,q-ET2RbZn(SCN)4,