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

Electron Orbits for a Magnetic Field along cH

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

But nesting at q=2kF

+/-

nG, G=2π/λ

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

Note: When

Δ>H0μ↑↓>

H

single pairs break

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

Injae

Lee

Δ=Hμ2

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?

Back to Magnetic Field Induced Decoupling/Decoherence

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

Field induced inter-chain decoupling

5

4

3

2

1

c'

e N

θ

Rzz

1 2 3 4 5a

Hc

a

T−∇

Hc

H

c

aaH

c

a

Hc

-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?