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Organic SuperconductivityB
CS@
50
Oct
ober
12,
200
7
Brief HistoryA Remarkable Set of Materials!
Nature of the Superconducting State?The Discovery of New Condensed Phases & New Effects in High Magnetic Fields
Δ=Hμ2
Triplet?
(TMTSF)2
PF6 the first organic superconductor
-50 -40 -30 -20 -10 0 10 20 30 40 50
-4
-2
0
2
4
6
-2L c'-1L 1L
2K 1K
N(μ
V/K)
θ
ControllableCoherence?
P. M. Chaikin, Center for Soft Matter Research, NYU
(TMTSF)2 PF6 - Most Remarkable Electronic Material Ever Discovered
So far in one single crystal:
All the usual competitions:Metal-Insulator, Magnetic-Superconductor,
Commensurate-Incommensurate, FermiLiquid-
NonFermiLiquid,Spin Density Wave -
Charge Density Wave……
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 EffectsTriplet Superconductivity, Field Induced Slabs
BC
S@50
O
ctob
er 1
2, 2
007
Who’s to Blame
UCLA•
Stuart Brown•
Gil Clark•
David Chow
Princeton•
InJae Lee (Chonbuk
National University) •
Weida Wu (Rutgers)
Boston College•
Mike Naughton
With Advice from: Andrei Lebed, Victor Yakovenko,Phil Anderson, David Huse, Phuan Ong
1911Superconductivity Discovered byGilles Holst
Superconductivity ExplainedBCS1957
1970
1963 Bill Little proposes Excitonic, Organic, Polymeric Superconductor
Schegolev, Bloch, Heeger,….Work on “1D” metals, TCNQ’s
TTF-TCNQ first organic metal (not superconductor)
Alan Heeger,others
Fred Wudl
discovers TTF
1975Rick Greene, (SN)x
, first (and only) polymeric superconductor Tc~0.3K
1973
Bechgaard
and Jerome First Organic Superconductor TMTSF2
PF6 Tc~1.2K1979
G. Saito, (ET)2
Cu[N(CN)2
Br] Tc~13K
1911Superconductivity Discovered byGilles Holst
Superconductivity ExplainedBCS1957
1970
1963 Bill Little proposes Excitonic, Organic, Polymeric Superconductor
Schegolev, Bloch, Heeger,….Work on “1D” metals, TCNQ’s
TTF-TCNQ first organic metal (not superconductor)
Alan Heeger,others
Fred Wudl
discovers TTF
1975Rick Greene, (SN)x
, first (and only) polymeric superconductor Tc~0.3K
1973
Bechgaard
and Jerome First Organic Superconductor TMTSF2
PF6 Tc~1.2K1979
G. Saito, (ET)2
Cu[N(CN)2
Br] Tc~13K
“g-ology
Phase Diagram 1D electrons
kF-kF kF-kF
ε ε
g1
(q=2kF
) g2
(q=0)
g2
g1
Only two interactions important
backscattering forward scattering
2kF
kF
-kF
kFkF
-qq = 2kF
1911Superconductivity Discovered byGilles Holst
Superconductivity ExplainedBCS1957
1970
1963 Bill Little proposes Excitonic, Organic, Polymeric Superconductor
Schegolev, Bloch, Heeger,….Work on “1D” metals, TCNQ’s
TTF-TCNQ first organic metal (not superconductor)
Alan Heeger,others
Fred Wudl
discovers TTF
1975Rick Greene, (SN)x
, first (and only) polymeric superconductor Tc~0.3K
1973
Bechgaard
and Jerome First Organic Superconductor TMTSF2
PF6 Tc~1.2K1979
G. Saito, (ET)2
Cu[N(CN)2
Br] Tc~13K
X
X
X
X R
R
R
R
TTF : X=S, R=HTSF : X=Se, R=HTTeF : X=Te, R=HTMTSF : X=Se, R=MeTMTTF : X=S, R=Me
X
X
X
X
Y1
Y1Y2
Y2
ET(BEDT-TTF) : X=Y1=Y2=SBO(BEDO-TTF) : X=S,Y1=Y2=OBETS(BEDT-TSF) : X=Se,Y1=Y2=SEOET : X=S,Y1=S,Y2=O
X
X
X
X
DBTTF : X=SDBTSF : X=Se
X
X
X
X
HMTTF : X=SHMTSF : X=SeHMTTeF : X=Te
S
S
S
S
S
SS
S
TTCn-TTF : X=STSeCn-TTF : X=SeTTeCn-TTF : X=Te
S
S
S
S
S
S
BET-TTF
X
X
X
X
OMTTF : X=SOMTSF : X=Se
S
S
S
S XCnH2n+1
XCnH2n+1H2n+1CnX
H2n+1CnX
S
S
S
S
S
SS
S
S
S
S
SS
SCnTET-TTF
CnH2n+1
CnH2n+1
S
S
S
S
S
SS
S
BMDT-TTF
BVDT-TTF
BPDT-TTF
S
S
S
SS
SMDT-TTF
Te
Te
Te
TeSS
Me
Me
Me
MeBDMT-TTeF
X X
X X
R
R
R
R
TTN : X=S, R=HTSN : X=Se, R=HTMTTeN : X=Te, R=Me
X X
X X
R2
R2
R1
R1
DMTTA : X=S, R1=H, R2=MeTMTTA : X=S, R1=R2==Me6,7-DMTTA : X=S, R1=H, R2=MeTSA : X=Se, R1=R2=HDMTSA : X=Se, R1=Me, R2=H6,7-DMTSA : X=Se, R1=H, R2=MeTMTSA : X=Se, R1=R2=MeDMTTeA : X=Te, R1=Me, R2=H
X X
Y YTTT : X=Y=S, R1=R2=R3=R4=HF2TTT : X=Y=S, R1=R2=R3=R4=HTST : X=Y=Se, R1=R2=F, R3=R4=HTTeT : X=Y=Te,R1=R2=R3=R4=H
R4
R3
R1
R2
S
S
R1
R1
DTPY : R1=R2=HMSDTPY : R1=SeMe,R2=HMTDTPY : R1=SMe,R2=HPh2DTPY : R1=Ph,R2=H3,8-(MeO)2DTPY : R1=H, R2=MeO
S
S
S
S
S
S
ETDTPY
R2
R2
S
S
S
SMe
Me S
S
TMDTDM-TTF
NMe2Me2N
NMe2Me2N
TDAE
NMe2Me2N
TMPD
X
X
X
X
Y1
Y1Y2
Y2
ET(BEDT-TTF) : X=Y1=Y2=SBO(BEDO-TTF) : X=S,Y1=Y2=OBETS(BEDT-TSF) : X=Se,Y1=Y2=SEOET : X=S,Y1=S,Y2=O
X
X
X
X R
R
R
R
TTF : X=S, R=HTSF : X=Se, R=HTTeF : X=Te, R=HTMTSF : X=Se, R=MeTMTTF : X=S, R=Me
Wudl
Yagubski
Saito
Quasi 1D
Quasi 2D
1911Superconductivity Discovered byGilles Holst
Superconductivity ExplainedBCS1957
1970
1963 Bill Little proposes Excitonic, Organic, Polymeric Superconductor
Schegolev, Bloch, Heeger,….Work on “1D” metals, TCNQ’s
TTF-TCNQ first organic metal (not superconductor)
Alan Heeger,others
Fred Wudl
discovers TTF
1975Rick Greene, (SN)x
, first (and only) polymeric superconductor Tc~0.3K
1973
Bechgaard
and Jerome First Organic Superconductor TMTSF2
PF6 Tc~1.2K1979
G. Saito, (ET)2
Cu[N(CN)2
Br] Tc~13K
Observed and hinted at ground statesBEDT-TTF family (TMTSF)2PF6
Supercond – singlet- d-wave?- LOFF?
FerromagneticSDWCDWQuantum Hall?Fermi-Liquid
Supercond – triplet?SDWCDWField Induced SDWQuantum HallFermi-LiquidNon – Fermi, Luttinger? LiqMott Insulator?
Crystal Structure of Bechgaard Salts (TMTSF)2
X
• Highly anisotropicσa
: σb
: σc
= 1 : 10-2
: 10-5
4ta : 4tb : 4tc = 1 : 0.1: 0.003 (eV)σi ~ ti
2
• Good metalρ ~1 μΩcm
at 4K (ρ
(Cu) ~ 1μΩcm at 300K).
• Extremely cleanl~10μ at 1K, h/τ~0.1K at 1K
• ¼
Filled, Slightly DimerizedSingle chain has charge gap.
7.297 , 7.711 , 13.522a b c= Α = Α = Αo o o
83.39 , 86.27 , 71.01α β γ= ° = ° = °
Triclinica
c b
n = 0
S D W
metal
sc
S D W
metal
metal
F I S D W
15
10
5
0
T(K
)
0
5
10
15
P(kbar)
0
5
10
15
20
25
30
H(tesla)
Q H E
Phase Diagram (TMTSF)2
PF6Woowon
Kang
1D metals are unstable – Fermi Surfaces NestInterchain hopping – warped Fermi Surface – regain metal
Pressure increases interchain hopping – more 3D
n = 0
S D W
metal
sc
S D W
metal
metal
F I S D W
15
10
5
0
T(K
)
0
5
10
15
P(kbar)
0
5
10
15
20
25
30
H(tesla)
Q H E
More 3D like
3D (P,H,T) phase diagram of (TMTSF)2
PF6
Insulator-Superconductor Bechgaard, Jerome 19791D-electron gas phase diagram (“g-ology”).J. Solyom, Adv. Phys 28, 201 (1979)
First guess from g-ology
SDWTS
(SS)
H // c-axis
SDW
SC
T(K
)
P(kbar)
g2
g1
P.M. Chaikin, M.Y. Choi and R.L. Greene, Mag. Mat. 31, 1268 (1983)
Resistive upper critical fields
M.Y. Choi et.al., Phys. Rev. B25, 6208 (1982)
Radiation damage experiments
Non s-wave Singlet (s,d-wave)?Hp =16 KG
Singlet or Triplet ?
M. Takigawa et.al.,J.Phys. Soc. Jpn. 56, 873 (1987)
Proton spin-lattice relaxation experiments
Thermal conductivity Belin
et. al.
S-wave (a finite gap) (No node on FS)
Non S-wave(line node on FS)
T3
Singlet –
Triplet Unresolved after ~ 12 years in 1980’s
But People discovered unusual things in Magnetic Fields
k space
kx
ky
Real Space
Bz
xy
Fv
One-Dimensionalized
by Magnetic
field
⎟⎟⎠
⎞⎜⎜⎝
⎛=
zF
bb Bev
tbw 4
f zb
ev bBω =
h
zebBh
=λ
Chaikin, Azbel, Holstein, ‘83
100
50
0
Rxy
(mΩ
)
60
30
0
Rxx
(mΩ
)
151050
B(tesla)
N = 1
N = 2
N = 3
N = 4
T = 300mK P = 10kbar
Integer Quantum Hall Effect in (TMTSF)2 PF6
Woowon
Kang
n = 0
S D W
metal
sc
S D W
metal
metal
F I S D W
15
10
5
0
T(K
)
0
5
10
15
P(kbar)
0
5
10
15
20
25
30
H(tesla)
Q H E
More 1D lik
eMore 3D like
Main lesson:
Magnetic field perpendicular to the chainsreduces electronic dimension
Does this decouple chains/planes?
H
bc
a
bc H=0
3D coherent Coherent planes
Two Contributions to Magnetic Critical Field -
Orbital and Spin
Orbital term derives from Field Expulsione.g. Meisner
Effect
Need currents to expel fieldj~H, ΔF~K.E. ~j2~H2
Spin derives from susceptibilityof spin paired state
ΔF~ -
(1/2)ΔχH2
FNormal
Fsuper
FNormal-
(1/2)
χPauliH2
FsuperH H
Hc2orbital
HPauli
Usually Hc2orbital
<<HPauliHc2orbital
HPauliH
TcT
F
L.I. Burlarchkov, L.P. Gor’kov and A.G. Lebed’Europhys. Lett., 4 941 (1987)
Test for the triplet superconducting pairing?
tc /Tc = 4
A.G. Lebed’/DMS’s proposal.Field-induced dimensional crossover quenches orbital pair breaking effect
tc /Tc = 7
H//y (b)
A.G. Lebed’, JETP Lett., 44, 114 (1986)N. Dupuis, G. Montambaux
and C.A.R. Sa de Melo, PRL., 70, 2613, (1993)
][84.12
TeslaTH co
p =Δ
=μ
a bH
c
0.0 0.3 0.6 0.9 1.2
0
1
2
3
4
5
6
PL
Junction
(TMTSF)2PF
6 P=6kbar
H // c*
H // a
H // b'M
agne
tic F
ield
(T)
temperature (K)
Injae
Lee
HC2
> 4 x HPauli
proves triplet (equal spin paired)
But people are more used to seeing NMR Knight Shift
↓↓↑↑ or
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
Miniature pressure cell mounted on the bottom of mixing chamber
1.2mm
1mm
Spin susceptibility in (TMTSF)2
PF6
(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?
P. Fulde and K. Maki, Phys. Rev. B139, A788 (1965)
0.0 0.5 1.0 1.5 2.0
0.5
1.0
0.63H/Hc2 = 0
H // a H // b
χ
/ χn
T / Tc(H)
I.J. Lee et al., PRL, 88, 17004 (2002)
n
n Ksω ωχ
χ−
=Singlet
Tiplet
On the superconducting state of the organic conductor (TMTSF)2ClO4J. 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 theparamagnetic limit. Nevertheless, the 77Se NMR Knight shift at low fields reveals a decrease inspin susceptibility s consistent with singlet spin pairing. The field dependence of the spin-latticerelaxation 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?
2/c π
2 /bπ
2 /aπ
ka
kc
kb
2k f
H
ωb
=evF
Hbcos(θ)/h
ωc
=evF
Hbsin(θ)/h
Lebed’s
magic Angles
Something happens when ωb
/ωc
= p/q
rational
θ
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
Lebed
Magic Angle Effects
ky
kz
B B
Recip
space Real space
Commensurate Orbits correspond to field directedbetween real space chains
⊥
Magic Angles Lattice Vectors
Woowon
KangR
xx
Strong, Clark, Anderson PRL 73, 1007 (1994)
Quasi-particle coherence
b
c Basic Idea: Coherent-Incoherent Transitionabove Threshold Hperp
field
0 5 10 15 200
1
2
3
4
5
6
7
8
9
0 5 10 15 200
1
2
3
4
5
6
7
8
9
0 5 10 15 200
1
2
3
4
5
6
7
8
9 2L3Max
bc
c 2L 3Max b 1Max c*
1L -1L 2Max
H=0
Rzz
, Ω
T , K
Chashechkina
These differ by 6o
ЧашечкинаAt magic angles metallicdR/dT>0
At nonmagic
angles Nonmetallic dR/dT<0
Similar effect alonga,b,c
axes
0
1
2
3
4
5
6
-100 -50 0 50 100angle (b-c rotation, b=90)
c ax
is con
ductan
ce
Look at Conductivity instead of resistivity
9.2T2T
.1T
Insulating when decoupledConducting when field allows
interchain
tunneling
-50 -40 -30 -20 -10 0 10 20 30 40 50
-4
-2
0
2
4
6
-2L c'-1L 1L
2K 1K
N(μ
V/K)
θ
Weida
WuAngular dependent Nernst
Drude, Boltzmann:
(TMTSF)2
PF6
: ~ 10 /Ne V Kμ
Giant Nernst Signal
-40 -20 0 20 40-8
-6
-4
-2
0
2
4
6
87.5 Tesla
-1L 1Lc'-2L
2K 1K 0.2K
e N (
μV /
K )
θ ( o )
KnVTT
ek
BTe
cF
B
N
/1
~
sin
≈
•∝
τω
θ
-40 -20 0 20 40-6.0
-4.0
-2.0
0.0
2.0
4.0
6.0
-1 +1c'
e N (
μV/K
)
θ
H
cb
a
-1
H
cb
a
c’ c
H
ba
+1
Transport:Only coherent at planes // H
What is the coherence?
SC Phase coherence at Magic Angle Planes
N.P. Ong, W. Wu, P. M. Chaikin and P. W. Anderson, EuroPhys. Lett. 66 (4)
579
(2004)
5
4
3
2
1
c '
e N
θ
Rzz
aa
H
c
a
H
c
va
T−∇
H
c
va
T−∇
Hc
1 2 3 4 5
H
c
Moon-Sun Nam, Arzhang
Ardavan, Stephen J. Blundell & John A. SchlueterVol
449 4 October 2007 1038/nature 06182Vortex Nernst
enhancedNear 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)2
PF6STILL MOST REMARKABLE ELECTRONIC MATERIAL?
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