Organic Superconductivity
P. M. Chaikin, Center for Soft Matter Research, NYU
Brief History
(TMTSF)2PF6 the first organic superconductor
Triplet?
6
2 μH = Δ
Controllable
Coherence?
2K
1K
4
N(μV/K)
BCS@50
October 12, 2007
A Remarkable Set of Materials!
Nature of the Superconducting State?
The Discovery of New Condensed Phases
& New Effects in High Magnetic Fields
2
0
-2
-2L
-4
c'
-1L
1L
-50 -40 -30 -20 -10 0 10 20 30 40 50
θ
(TMTSF)2PF6 - Most Remarkable Electronic
Material Ever Discovered
October 12, 2007
All the usual competitions:
Metal-Insulator, Magnetic-Superconductor,
Commensurate-Incommensurate, FermiLiquid- NonFermiLiquid,
Spin Density Wave - Charge Density Wave……
BCS@50
So far in one single crystal:
Exhibits all transport mechanisms known to man:
Metallic, Sliding Density Wave, Superconducting,
Quantum Hall
Plus somethings new :
Field Induced SDW/QHE
Giant Nernst Effect, Magic Angle Effects
Triplet Superconductivity, Field Induced Slabs
Who’s to Blame
Princeton
• InJae Lee (Chonbuk National University)
• Weida Wu (Rutgers)
UCLA
• Stuart Brown
• Gil Clark
• David Chow
Boston College
• Mike Naughton
With Advice from: Andrei Lebed, Victor Yakovenko,
Phil Anderson, David Huse, Phuan Ong
Superconductivity Discovered by
Gilles Holst
1911
Superconductivity Explained
BCS
1957
Bill Little proposes Excitonic,
Organic, Polymeric Superconductor
1963
Schegolev, Bloch, Heeger,….
Work on “1D” metals, TCNQ’s
Fred Wudl discovers TTF
1970
TTF-TCNQ first organic metal
(not superconductor)
1973
Rick Greene, (SN)x , first (and only)
polymeric superconductor Tc~0.3K
Bechgaard and Jerome First Organic
Superconductor TMTSF2 PF6 Tc~1.2K
G. Saito, (ET)2Cu[N(CN)2Br] Tc~13K
Alan Heeger,
others
1975
1979
Superconductivity Discovered by
Gilles Holst
1911
Superconductivity Explained
BCS
1957
Bill Little proposes Excitonic,
Organic, Polymeric Superconductor
1963
Schegolev, Bloch, Heeger,….
Work on “1D” metals, TCNQ’s
Fred Wudl discovers TTF
1970
TTF-TCNQ first organic metal
(not superconductor)
1973
Rick Greene, (SN)x , first (and only)
polymeric superconductor Tc~0.3K
Bechgaard and Jerome First Organic
Superconductor TMTSF2 PF6 Tc~1.2K
G. Saito, (ET)2Cu[N(CN)2Br] Tc~13K
Alan Heeger,
others
1975
1979
“g-ology Phase Diagram 1D electrons
g1
kF
g2
-kF
2kF
kF-q
Only two interactions important
q = 2kF
kF
ε
ε
backscattering
forward scattering
kF
-kF
g1(q=2kF)
-kF
kF
g2(q=0)
Superconductivity Discovered by
Gilles Holst
1911
Superconductivity Explained
BCS
1957
Bill Little proposes Excitonic,
Organic, Polymeric Superconductor
1963
Schegolev, Bloch, Heeger,….
Work on “1D” metals, TCNQ’s
Fred Wudl discovers TTF
1970
TTF-TCNQ first organic metal
(not superconductor)
1973
Rick Greene, (SN)x , first (and only)
polymeric superconductor Tc~0.3K
Bechgaard and Jerome First Organic
Superconductor TMTSF2 PF6 Tc~1.2K
G. Saito, (ET)2Cu[N(CN)2Br] Tc~13K
Alan Heeger,
others
1975
1979
R
X
X
R
R
X
Wudl
X
R
X
X
R
Y2
X
X
Y1
R
X
X
R
Y2
X
X
Y1
TTF : X=S, R=H
TSF : X=Se, R=H
TTeF : X=Te, R=H
TMTSF : X=Se, R=Me
TMTTF : X=S, R=Me
Quasi 1D
X
X
ET(BEDT-TTF) : X=Y1=Y2=S
BO(BEDO-TTF) : X=S,Y1=Y2=O
BETS(BEDT-TSF) : X=Se,Y1=Y2=S
EOET : X=S,Y1=S,Y2=O
X
X
OMTTF : X=S
OMTSF : X=Se
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
Te
Te
Te
S
BMDT-TTF
X
X
S
S
S
S
S
X
Y2
X
X
Y1
ET(BEDT-TTF) : X=Y1=Y2=S
BO(BEDO-TTF) : X=S,Y1=Y2=O
BETS(BEDT-TSF) : X=Se,Y1=Y2=S
EOET : X=S,Y1=S,Y2=O
R
R
X
X
TTN : X=S, R=H
TSN : X=Se, R=H
TMTTeN : X=Te, R=Me
X
R2
R1
R2
R1
X
Quasi 2D
X
S
S
S
S
S
S
S
S
S
S
S
H2n+1CnX
S
S
XCnH2n+1
H2n+1CnX
S
S
XCnH2n+1
TTCn-TTF : X=S
TSeCn-TTF : X=Se
TTeCn-TTF : X=Te
X
DMTTA : X=S, R1=H, R2=Me
TMTTA : X=S, R1=R2==Me
6,7-DMTTA : X=S, R1=H, R2=Me
TSA : X=Se, R1=R2=H
DMTSA : X=Se, R1=Me, R2=H
6,7-DMTSA : X=Se, R1=H, R2=Me
TMTSA : X=Se, R1=R2=Me
DMTTeA : X=Te, R1=Me, R2=H
S
S
S
CnH2n+1
S
S
S
CnTET-TTF
CnH2n+1
S
X
X
R1
R4
S
R1
R2
Y
Y
TTT : X=Y=S, R1=R2=R3=R4=H
F2TTT : X=Y=S, R1=R2=R3=R4=H
TST : X=Y=Se, R1=R2=F, R3=R4=H
TTeT : X=Y=Te,R1=R2=R3=R4=H
R2
S
R2
R1
DTPY : R1=R2=H
MSDTPY : R1=SeMe,R2=H
MTDTPY : R1=SMe,R2=H
Ph2DTPY : R1=Ph,R2=H
3,8-(MeO)2DTPY : R1=H, R2=MeO
Saito
Me2N
NMe2
Me
NMe2
Me2N
Me2N
NMe2
TDAE
S
S
R3
Yagubski
X
BET-TTF
X
R
S
Me
X
R
X
BVDT-TTF
BDMT-TTeF
MDT-TTF
Y1
S
S
Me
S
S
Me
Te
X
HMTTF : X=S
HMTSF : X=Se
HMTTeF : X=Te
BPDT-TTF
Me
X
X
X
DBTTF : X=S
DBTSF : X=Se
R
TTF : X=S, R=H
TSF : X=Se, R=H
TTeF : X=Te, R=H
TMTSF : X=Se, R=Me
TMTTF : X=S, R=Me
Y2
X
TMPD
Me
S
S
S
S
S
S
TMDTDM-TTF
S
S
S
ETDTPY
Superconductivity Discovered by
Gilles Holst
1911
Superconductivity Explained
BCS
1957
Bill Little proposes Excitonic,
Organic, Polymeric Superconductor
1963
Schegolev, Bloch, Heeger,….
Work on “1D” metals, TCNQ’s
Fred Wudl discovers TTF
1970
TTF-TCNQ first organic metal
(not superconductor)
1973
Rick Greene, (SN)x , first (and only)
polymeric superconductor Tc~0.3K
Bechgaard and Jerome First Organic
Superconductor TMTSF2 PF6 Tc~1.2K
G. Saito, (ET)2Cu[N(CN)2Br] Tc~13K
Alan Heeger,
others
1975
1979
Observed and hinted at ground states
BEDT-TTF family
(TMTSF)2PF6
Supercond – triplet?
Supercond – singlet
SDW
d-wave?
CDW
LOFF?
Field Induced SDW
Ferromagnetic
Quantum Hall
SDW
Fermi-Liquid
CDW
Non – Fermi, Luttinger? Liq
Quantum Hall?
Mott Insulator?
Fermi-Liquid
Crystal Structure of Bechgaard Salts (TMTSF)2X
• Highly
anisotropic
σa : σb : σc = 1 : 10-2 : 10-5
4ta : 4tb : 4tc = 1 : 0.1: 0.003 (eV)
σi ~ ti2
• Good metal
ρ ~1 μΩcm at 4K
(ρ (Cu) ~ 1μΩcm at 300K).
c
b
• Extremely clean
a
l~10μ at 1K, h/τ~0.1K at 1K
Triclinic
α = 83.39°, β = 86.27°, γ = 71.01°
o
o
o
a = 7.297 Α, b = 7.711Α, c = 13.522 Α
• ¼ Filled, Slightly Dimerized
Single chain has charge gap.
Woowon Kang
Phase Diagram (TMTSF)2PF6
ta
me
l
15
S
D
meta
l
W
F
D
W
T(K)
10
I S
n =
0
5
SD
W
QH
0
30
E
25
sc
0
20
5
P(k
bar)
10
15
meta
l
10
5
15
0
te
H(
sla
)
1D metals are unstable – Fermi Surfaces Nest
Interchain hopping – warped Fermi Surface – regain metal
Pressure increases interchain hopping – more 3D
ta
me
l
15
S
D
meta
l
W
F
D
W
T(K)
10
I S
n =
0
5
SD
W
QH
0
30
E
25
sc
0
20
5
Mo
re 3
D
P(k
bar)
10
15
meta
l
10
5
15
like
0
)
sla
e
t
H(
3D (P,H,T) phase diagram of (TMTSF)2PF6
First guess from g-ology
T(K)
g1
TS
(SS)
SD
SDW
g2
W
P( k b
ar)
SC
H
//
s
i
x
c-a
Insulator-Superconductor Bechgaard, Jerome 1979
1D-electron gas phase diagram
(“g-ology”).
J. Solyom, Adv. Phys 28, 201 (1979)
Singlet or Triplet ?
Radiation damage experiments
Resistive upper critical fields
Hp=16 KG
Non s-wave
M.Y. Choi et.al., Phys. Rev. B25, 6208 (1982)
Singlet (s,d-wave)?
P.M. Chaikin, M.Y. Choi and R.L. Greene, Mag. Mat. 31, 1268 (1983)
Proton spin-lattice relaxation experiments
T3
M. Takigawa et.al.,
J.Phys. Soc. Jpn. 56, 873 (1987)
Non S-wave
(line node on FS)
Belin et. al.
Thermal conductivity
S-wave (a finite gap)
(No node on FS)
Singlet – Triplet Unresolved
after ~ 12 years in 1980’s
But People discovered unusual things in Magnetic Fields
Electron Orbits for a Magnetic Field along c
H
One-Dimensionalized by Magnetic field
k space
Real Space
⎛ 4tb
wb = b⎜⎜
⎝ evF Bz
⎞
⎟⎟
⎠
y
h
λ=
ebB z
x
ωb =
Chaikin, Azbel, Holstein, ‘83
ev f bBz
h
Bz
ky
kx
vF
But nesting at q=2kF +/- nG, G=2π/λ
Woowon Kang
Integer Quantum Hall Effect in (TMTSF)2PF6
100
N=1
Rxy(mΩ)
T = 300mK
P = 10kbar
50
N=2
N=3
N=4
0
Rxx(mΩ)
60
30
0
0
5
10
B(tesla)
15
ta
me
l
15
S
D
meta
l
W
F
D
W
T(K)
10
I S
n =
0
5
SD
W
QH
0
30
E
25
sc
0
20
5
Mo
re 3
D
P(k
bar)
10
15
meta
l
10
5
15
like
)
sla
e
t
H(
0
D
1
e
r
o
M
il ke
Main lesson:
Magnetic field perpendicular to the chains
reduces electronic dimension
Does this decouple chains/planes?
c
H=0
b
c
a
3D coherent Coherent planes
b
H
Two Contributions to Magnetic Critical Field - Orbital and Spin
Spin derives from susceptibility
of spin paired state
Orbital term derives from Field Expulsion
e.g. Meisner Effect
Need currents to expel field
j~H, ΔF~K.E. ~j2~H2
F
FNormal
ΔF~ - (1/2)ΔχH2
FNormal
Hc2orbital
Fsuper
Usually Hc2orbital <<HPauli
Fsuper
H
H
- (1/2) χPauliH2
Hc2orbital
T
HPauli
HPauli
Tc
H
Note: When
↑↓>
μ0 H > Δ
H
single pairs break
A.G. Lebed’/DMS’s proposal.
Field-induced dimensional crossover quenches orbital pair breaking effect
A.G. Lebed’, JETP Lett., 44, 114 (1986)
N. Dupuis, G. Montambaux and C.A.R. Sa de Melo, PRL., 70, 2613, (1993)
c
H//y (b)
H
tc/Tc = 7
tc/Tc = 4
b
a
Test for the triplet
superconducting pairing?
Hp =
L.I. Burlarchkov, L.P. Gor’kov and A.G. Lebed’
Europhys. Lett., 4 941 (1987)
Δ
= 1.84Tc [Tesla ]
2μo
Junction
6
(TMTSF)2PF6
P=6kbar
Magnetic Field (T)
5
H // b'
4
3
2
PL
H // a
1
H // c*
0
0.0
0.3
0.6
0.9
temperature (K)
1.2
Injae Lee
Injae Lee
2 μH = Δ
HC2 > 4 x HPauli proves triplet (equal spin paired)
↑↑ or ↓↓
But people are more used to seeing NMR Knight Shift
Setup for 77Se NMR Knight Shift experiments
• Dilution temperature (0.03 K)
• High pressure (7 kbar)
• Precise angular alignment (resolution: 0.0025o)
• Simultaneous NMR and transport measurements
1mm
Miniature pressure cell mounted on
the bottom of mixing chamber
1.2mm
Spin susceptibility in (TMTSF)2PF6
Tiplet
χ / χn
1.0
0.5
H // a
H // b
Singlet
ω − ω
χ
=
χn
Ks
n
0.63
H/Hc2 = 0
0.0
0.5
1.0
1.5
2.0
P. Fulde and K. Maki,
Phys. Rev. B139, A788 (1965)
T / Tc(H)
I.J. Lee et al., PRL, 88, 17004 (2002)
(H=2.38T)/(Hc2(0) =5T) ~ 0.5 for H // b
(H=1.43T)/(Hc2(0)=3.4T) ~ 0.4 for H // a
Spin triplet superconductivity?
On the superconducting state of the organic conductor (TMTSF)2ClO4
J. Shinagawa,1 Y. Kurosaki,1,2 F. Zhang,1 C. Parker,1,3
S. E. Brown,1 D. J´erome,4 J. B. Christensen,5 and K. Bechgaard5
(Dated: April 9, 2007)
(TMTSF)2ClO4 is a quasi-one dimensional organic conductor and superconductor with Tc = 1.4K,
and one of at least two Bechgaard salts observed to have upper critical fields far exceeding the
paramagnetic limit. Nevertheless, the 77Se NMR Knight shift at low fields reveals a decrease in
spin susceptibility s consistent with singlet spin pairing. The field dependence of the spin-lattice
relaxation rate at 100mK exhibits a sharp crossover (or phase transition) at a field Hs ∼ 15kOe, to
a regime where s is close to the normal state value, even though Hc2 ≫ Hs.
But at low field there is a Knight Shift shift?
Back to Magnetic Field Induced
Decoupling/Decoherence
Lebed’s magic Angles
Something happens when
ωb/ωc = p/q rational
H
kc
2k f
θ
ωc=evFHbsin(θ)/h
2π/c
kb
ka
/a
π
2
2 π/b
ωb=evFHbcos(θ)/h
Lebed Magic Angle Effects
A.G. Lebed, “Anisotropy Of An Instability For A Spin-Density Wave-Induced
By A Magnetic-Field In A Q1D Conductor”, JETP Lett. 43, 174 (1986).
A. G. Lebed, P. Bak, “Theory Of Unusual Anisotropy Of Magnetoresistance In
Organic Superconductors”, Phys Rev Lett 63, 1315 1989
Commensurate Orbits correspond to field directed
between real space chains
Magic Angles Æ Lattice Vectors
B
B
kz
ky
Recip space
⊥
Real space
Quasi-particle coherence
Rxx
Woowon Kang
Basic Idea:
Coherent-Incoherent Transition
above Threshold Hperp field
c
b
Strong, Clark, Anderson
PRL 73, 1007 (1994)
At magic angles metallic
dR/dT>0
9
2L
c
2L
3Max
b
1Max
*
c
1L
-1L
2Max
3Max
8
At nonmagic angles
Nonmetallic dR/dT<0
7
6
These differ by 6o
Rzz , Ω
5
4
3
H=0
2
1
Similar effect along
a,b,c axes
b
c
0
0
5
10
T,K
15
20
Chashechkina
Чашечкина
Look at Conductivity instead of resistivity
6
.1T
ca
xisc
o
n
d
u
c
tan
c
e
5
4
3
2
2T
9.2T
1
0
-100
-50
0
50
a ngle (b-c rota tion, b=90)
Insulating when decoupled
Conducting when field allows
interchain tunneling
100
Weida Wu
Angular dependent Nernst
6
2K
1K
N(μV/K)
4
2
0
-2
-2L
-4
c'
-1L
1L
-50 -40 -30 -20 -10 0 10 20 30 40 50
θ
Giant Nernst Signal
8
2K
7.5 Tesla
1K
6
0.2K
eN ( μV / K )
4
eN ∝ T • B sin θ
kB T
ωcτ
~
e TF
2
0
≈ 1nV / K
-2
(TMTSF)2PF6: eN ~ 10 μV / K
-4 -2L
c'
-1L
-6
-8
Drude, Boltzmann:
-40
-20
0
o
θ( )
1L
20
40
Field induced inter-chain decoupling
5
3
1
Rzz
eN
c' 4
2
θ
H
H
c
−∇T
H
c
c
c
c
H
a
1
a
2
a
3
a
4
a
5
H
6.0
eN ( μV/K )
4.0
2.0
0.0
-2.0
-4.0
-6.0
b
a
-40
-1
-20
0
θ
20
b
c
H
+1
c'
-1
Transport:
Only coherent
at planes // H
40
c’
a
What is the coherence?
c
H
b
+1
c
a
H
SC Phase coherence at Magic Angle Planes
e
zz
5
3
1
R
N
c' 4
2
H
−∇T
a
H
c −∇T
1
a
θ
c
c
v
2
a
H
3
a
v
4
c
c
H
H
a
5
N.P. Ong, W. Wu, P. M. Chaikin and P. W. Anderson, EuroPhys. Lett. 66 (4) 579 (2004)
Moon-Sun Nam, Arzhang Ardavan,
Stephen J. Blundell & John A. Schlueter
Vol 449 4 October 2007 1038/nature 06182
Vortex Nernst enhanced
Near Mott Insulator
Summary
• 2D organics - S and D wave Superconductors,
• 1D organics - Singlet and Triplet superconductors,
• Strong fields control dimensionality and coherence.
• Organic Superconductors remain an exciting testing
ground for low dimensional strongly interacting electrons
with characteristic energies HTc/10
(TMTSF)2PF6
STILL MOST REMARKABLE ELECTRONIC MATERIAL?