Transcript Hong Kong Forum of Condensed Matter Physics

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. 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 materials
Possible carrier doping into DNA
4) Future
Electronic properties of molecular assemblies
Electronic properties of interfaces and contacts
HF: JPSJ 75(2006)051001
Molecular Conducting Crystals
NMP-TCNQ
CT Mott
insulator
1d AF(TCNQ)
TTF-TCNQ
CT 1d semimetal
p-dep. n
Peierls transition, CDW,
gigantic conductivity peak, sliding conduction
(CH)x
Peierls insulator
(Dimer)
doping , carriers as ingap states (solitons)
TMTCF2X
CT metal
SDW, SC, AF, Spin-Peierls, CO, ferroelectricity
DCNQI2X
CT metal
CO(Ag), CO-Mott with Peierls (Cu)
BEDTTTF2X
(ET2X)
CT metal
Mott Insulator, Charge Ordering, SC
BETS2X
CT metal
SC (GaCl4),
Mott insulator & Field-Induced SC(FeCl4)
(DT-TTF)2[Au(mnt)]
1/4 -filled
Spin Ladder
Charge Ordering ?
(TTM-TTP)I3
1 : 1 Half-filled
CT metal
Mott Transition
I3 --> FeBr1.8Cl2.2 : Fe +3
Single Component
Metal
HOMO-LUMO overlap->semimetal,
magnetic phase transition
Ni(tmdt)2
Au(tmdt)2
S= 5 / 2
Peierls Transition
TTF-TCNQ
CDW:
Combined degrees of freedom of
electrons and lattice distortions
Collective mode: Phason
Lee-Rice -Anderson(1974)
"superconducting fluctuations"
Impurity Pinning
Phase Hamiltonian :
HF(1976)
2)weak pinning : ε<< 1
fluctuations of potential
=> collective effects
Cf. Larkin-Ovchinikov: vortices
Parameter : ε=V0/nivF
HF-Lee (1978)
１）strong pinning : ε>> 1
=>
In 3d : Lee-Rice
“ Fukuyama - Lee - Rice ” (1987.9.4)
Theory of Friction
"Theoretical Studies of Friction:
One-dimensional Clean Surface"
“ Current driven
magnetic domain wall motion”
Matsukawa-HF, PRB (1994)
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
Molecular Conducting Crystals
NMP-TCNQ
CT Mott
insulator
1d AF(TCNQ)
TTF-TCNQ
CT 1d semimetal
p-dep. n
Peierls transition, CDW,
gigantic conductivity peak, sliding conduction
(CH)x
Peierls insulator
(Dimer)
doping , carriers as ingap states (solitons)
TMTCF2X
CT metal
SDW, SC, AF, Spin-Peierls, CO, ferroelectricity
DCNQI2X
CT metal
CO(Ag), CO-Mott with Peierls (Cu)
BEDTTTF2X
(ET2X)
CT metal
Mott Insulator, Charge Ordering, SC
BETS2X
CT metal
SC (GaCl4),
Mott insulator & Field-Induced SC(FeCl4)
(DT-TTF)2[Au(mnt)]
1/4 -filled
Spin Ladder
Charge Ordering ?
(TTM-TTP)I3
1 : 1 Half-filled
CT metal
Mott Transition
I3 --> FeBr1.8Cl2.2 : Fe +3
Single Component
Metal
HOMO-LUMO overlap->semimetal,
magnetic phase transition
Ni(tmdt)2
Au(tmdt)2
S= 5 / 2
A2 B
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
semiconductors
Anderson localization
Si
Band insulator + impurities
=> Small amount of carriers
=> Easy to control
=> Switchable
Insulator
Metal
FET
Carrier Doping into Insulators＝> Metallic Conduction
20
Superconductivity in B-doped Diamonds
and even in Silicon !
E. A. Ekimov et al., Nature 428, 542 (2004)
Takano et al. (2005)
Strong Disorder
,
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
Typical Molecular Conductors
A2B
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 !
Systematic Studies on
the Electronic Properties of Molecular Solids
Effects of mutual interactions
Extended Hubbard Model
H = Σ ti,i+1 ( cis† ci+1s + h.c. ) + Σ U ni↓ni↑ + Σ Vi,i+1 ni ni+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)
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
• case 1 : strong dimerization t1 >> t2
+ on-site Coulomb interaction U
S=1/2 per dimer
dimer Mott-Hubbard insulator
(uniform charge density)
• case 2 : intersite Coulomb
interaction V
S=1/2 on every other site
Wigner Crystal type Charge Ordering
TMTSF2X, TMTTF2X
“Jerome’s phase diagram”
Jerome et al. : ‘80s ~
“1d ”
molecule
TMTSF
H3C
Se
Se
CH 3
H3C
Se
Se
CH 3
TMTTF :
Se → S
crystal structure
TMTSF
PF6 -
demonstration : high pressure study on TMTTF2PF6
Metal-Insulator transition : nesting of Fermi surface
54kbar
8kbar
18kbar
52kbar
66kbar
47kbar
Adachi-Ojima-Kato-Kobayashi-Miyazaki-Tokumoto-Kobayashi ‘00
Charge Order in TMTTF2X ‐1‐
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 ‐2‐
13C-NMR
TMTTF2AsF6
dielectric constant
AsF6
SbF6
PF6
Monceau-Nad-Brazovskii PRL ‘01
Ferroelectricity !!
Chow et al PRL ’00
Zamborsky et al PRB ‘02
“Jerome’s
NEW phase
phasediagram
diagram”
ET=BEDT-TTF :
S
S
S
S
S
S
S
S
“ 2d ”
variety in in-plane (2d) lattice structures : polytypes a, b, q, k, l, …
quasi-2-D
crystal structure
mean-field calculations on Hubbard models
→ systematic understanding of ground states
ET
Kino-Fukuyama JPSJ ’95,’96
Degree of anisotropy of
triangular lattice
C.Hotta, JPSJ 72, 840(2003); H.Seo,C.Hotta,HF: Chemical Reviews
ET2X:κ and λ 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
Dimer ET forms triangle
S
S
S
S
S
H. Kino & H. Fukuyama, JPSJ (1995).
S
b1 >> b2, p, q
ET+0.5
S
t = (p| + |q|)/2
t' = b2/2
S
X-1
conducting
ET layer
Insulating
anion layer
t’/t : 0.5 ~ 1.0
Courtesy of Kanoda
Large frustration!?
k-(ET)2X ~ 2D triangular lattice
with half-filled band
In-plane structure is modeled to
anisotropic
triangular lattice
layered structure
ET
Conducting layer
Insulating layer
Kino-HF,JPSJ
Mott insulator
U/W
X
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
1/2 filled
0
1
Hole number / dimer
2
Mott insulator
Mott insulator
SC
SC
SC
1H-NMR
k-(ET)2Cu2(CN)3
(t’/t =1.05)
H (2.2 T)  2D plane
No splitting!
No broadening
spectra
k-(ET)2Cu[N(CN)2]Cl
(t’/t =0.74)
H (3.7 T)  2D plane
moment < 0.01mB
if any
FFT of Solid echo signal
No magnetic order!
spin liquid state
Antiferromagnetic
order below 27 K
(0.45mB)
Degree of anisotropy of
triangular lattice
C.Hotta, JPSJ 72, 840(2003); H.Seo,C.Hotta,HF: Chemical Reviews
ET2X with no/weak dimerization
q-type
q-ET2RbZn(SCN)4
a-type
a-ET2I3
Bender et al. ’84
N.Tajima et al. ‘00
Rothaemel et al. ’86
H.Mori, S.Tanaka, T.Mori ‘98
ET2X with no/weak dimerization ‐charge order‐
q-ET2RbZn(SCN)4
1D Heisenberg chain,
uniform J ~ 450K
(experiments : J ~ 160K)
Seo (2000)
a-ET2I3
1D alternating Heisenberg chain
J1 ~ 1000K, J2 ~ 200K
(experiments : J1 ~ 500K, J2 ~ 100K)
=> Singlet ground state
Cf. TMTCF2X: Seo, Monceau , Brown,
"Viscous" electron liquid
q-type
a-type
q-ET2RbZn(SCN)4
a-ET2I3
H.Mori, S.Tanaka, T.Mori ‘98
Above (or Near) CO,
resistivity is large and
almost temperature-independent
H.Mori(1998)
with low energy dynamics.
=>Viscous electron liquid.
Bender et al. ’84
N.Tajima et al. ‘00
By NMR: Takahashi, Kanoda
Frustrations between different spatial pattern of CO
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
“Neutrino” in Solids
S. Kobayashi, A. Kobayashi and Y. Suzumura, cond-mat/0601068
New Particles in α-ET2I3
H = v( kxσx + kyσy ) for graphene
Weyl eq. for neutrino
H = k・Vρσρ
for α-ET2I3
σ0 = 1, σα Pauli Matrix
A. Kobayashi
Hall effects and orbital magnetism
persistent current vs. dissipative current
Inter-band effects of magnetic field
Single Component
Molecular Metals
A.Kobayashi-Tanaka-H.Kobayashi(2001)
[Ni(tmdt)2]
S
S
S
S
S
S
b*
Ni
S
S
S
S
S
S
S. Ishibashi
b*
a*
a*
C* c*
c*
・The observation of dHvA oscillation
(510 Tesla ~ 10% of the 1st Brillouin zone)
H. Tanaka, M. Tokumoto (AIST), J. Brooks(NHMFL/FSU)
1st principles density functional calculation
......E. Canadell et al.
Π-d Crystals
- Metals in the sea of π-electrons * DCNQI2Cu : Valence fluctuations
*λ-BETS2FeCl4
magnetic 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)
Phthalocyanine, MPc
Craciun et al.(2005)
M= Fe, Co, Ni, Cu, Zn, Mg
Cf. Cu(F8Pc),Cu(F16Pc): N. Sato
So far, crystals of molecules.
How about
non-crystalline materials?
1) Myoglobin
2) DNA
Shin-Tarada-Tokushima-Miyajima-Taguchi (ISSP-RIKEN)
Local structure around Heme
in proteins
porphyrin
ヒスチジン
Histidine
Courtesy of Shin
4 possible electronic states of Fe in Myoglobin
By changing the spin and electron
valency, Myoglobin catches and releases
the various gases
S=2
(deoxy)
Fe
S=5/2
(H2O)
High spin
Histidine
Fe2+
Fe3+
O2
Fe
Histidine
Courtesy of Shin
Low spin
S=0
(O2,CO)
S=1/2
(CN,N3)
SXES
Shin (ISSP) SP-BL17
DOS of valence states
非占有
Alowed transition
EF Transition elements 2p,3p → 3d
価電子
rare earth elements ･･3d,4d → 4f
light element ･･･
1s → 2p
占有
hn
hn ’
hn
内殻
O2p, N2p, C2p DOS
hn ’
Fe 3d DOS
Fe dd励起
Theory（Cluster model）
O
N
N
Fe
N
N
N
Hamiltonian
Fe 3d
Fe 2p
Ligand 2p
Fe 3d – Ligand 2p hybridization
Fe 3d Coulomb interaction
Fe 2p-3d core-hole potential
ＤＮＡ
提供：マウロ（真宇呂）・ボエロ氏
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 ?
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 ?
“Contact problem”
Cf.井上
A Possible Origin of Carrier Doping into DNA
J.Phys.Soc.Jpn73(04)#8 p.2089
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 -
Electronic structure of DNA hydrate v.s.
anhydrous Mg
[(dG)2Mg(H2O)n]+
PO4-1
Mg2+
PO4-1
C
G
hydrated Mg
cations
LUMO
anhydrous Mg
cation
(c’)
(c)
(GGA/PBE gap~0.7eV)
Mg2+
Sz=0
HOMO
(b)
(c’) SOMO Sz=1
(a)
(b)
(a)
Unoccupied state
Occupied state
B
(a)
LUMO@G
(b) LUMO
7.6 eV
(b)
(c)
G
Mg+
(c’)
G
Calc. UHF/6-31G(d)
Electronic structure of dry DNA
[(dG) 2-Mg2+]
poly(dG)-poly(dC)
with anhydrous Mg
LUMO
impurity
m
G HOMO
hole
m
HOMO(G)
DOS(dopant)
DOS(host)
Similar to doped semiconductors for divalent cations( cf. SiP)
＝＞metallic DNA ? M+1: Ｓ＝1/2
Not for monovalent cations
DNA XES and XAS
The aim of the basic study on
1. electronic structure
2. transport properties
Adenine
Recent conductivity
measurements on DNA
Importance of the electronic
study
 nanostructure materials
 new semiconductors
Guanine
base pair
Cytosine
Thymin
e
Courtesy of Shin
N1s XAS of nucleobases
T
Intensity (arb. units)
C
G
A
N1s XAS of nucleobases
吸収端のπ*ピークはサイト選択的
-N=結合(imine)サイト
-N- 結合(amine)サイト
→励起エネルギーを選べば特定のサイトの情報が得ら
れる
-N- 結合(amine)サイトのπ* (Guanine & Cytosine)
→糖＋リン酸結合により高エネルギー側にシフト
dimer
nucleobase
400
405
410
415
Excitation energy (eV)
imine site
amine site
guanine
cytosine
→６員環におけるπ軌道のaromaticな性質が崩
れて電荷の偏りを生じている？
By Shin
N1s resonant XES of nucleobases
-N=結合(imine)サイトへの共鳴励起
→-N=結合サイトのoccupied DOSが得られる
N1s RXES of nucleobases
calculation
experiment
(gaussian 6-31G(d,p))
x
Intensity (arb.units)
T
x
x
→guanineのメインバンドから分離した状態が
HOMOを形成
C
G
A
-14
-12
-10
-8
-6
-4
-2
Binding Energy (eV)
N2p partial DOS of dimer DNA
Harada et al., Journal of Physical Chemistry A, 2006,110 13227
Kino et al., J.Phys.Soc.Japan 73,2089(2004)
SUMMARY
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.
4) Non-crystalline molecular materials
Shin : Possible carrier doping into DNA
d-d excitation spectra at Fe in myoglobin
=> First solid state type studies on proteins and DNA
4) Future
Electronic properties of molecular assemblies