Organic Superconductivity P

Organic Superconductivity P. M. Chaikin, Center for Soft Matter Research, NYU Brief History A Remarkable Set of Materials! Nature of the Superconducting State? The Discovery of New Condensed Phases & New Effects in High Magnetic Fields October 12, 2007 October 12, (TMTSF)2PF6 the first organic superconductor Controllable

6 Coherence? Triplet? 2K 4 1K

BCS@50 BCS@50 2 V/K) μ 0 N(

2μH Δ= -2 -2L -4 -1L c' 1L

-50 -40 -30 -20 -10 0 10 20 30 40 50 θ (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…… October 12, 2007 October 12, Exhibits all transport mechanisms known to man: Metallic, Sliding Density Wave, Superconducting, Quantum Hall

BCS@50 BCS@50 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 1911 Gilles Holst

Superconductivity Explained 1957 BCS

Bill Little proposes Excitonic, 1963 Organic, Polymeric Superconductor Schegolev, Bloch, Heeger,…. Fred Wudl discovers TTF Work on “1D” metals, TCNQ’s 1970

TTF-TCNQ first organic metal 1973 Alan Heeger, (not superconductor) others

Rick Greene, (SN)x , first (and only) 1975 polymeric superconductor Tc~0.3K

Bechgaard and Jerome First Organic 1979 Superconductor TMTSF PF Tc~1.2K 2 6

G. Saito, (ET)2Cu[N(CN)2Br] Tc~13K

Superconductivity Discovered by 1911 Gilles Holst

Superconductivity Explained 1957 BCS

Bill Little proposes Excitonic, 1963 Organic, Polymeric Superconductor Schegolev, Bloch, Heeger,…. Fred Wudl discovers TTF Work on “1D” metals, TCNQ’s 1970

TTF-TCNQ first organic metal 1973 Alan Heeger, (not superconductor) others

Rick Greene, (SN)x , first (and only) 1975 polymeric superconductor Tc~0.3K

Bechgaard and Jerome First Organic 1979 Superconductor TMTSF PF Tc~1.2K 2 6

G. Saito, (ET)2Cu[N(CN)2Br] Tc~13K

“g-ology Phase Diagram 1D electrons g1

-kF g2 2kF

kF-q kF Only two interactions important q = 2kF ε ε backscattering forward scattering

-kF kF -kF kF

g1(q=2kF) g2(q=0)

Superconductivity Discovered by 1911 Gilles Holst

Superconductivity Explained 1957 BCS

Bill Little proposes Excitonic, 1963 Organic, Polymeric Superconductor Schegolev, Bloch, Heeger,…. Fred Wudl discovers TTF Work on “1D” metals, TCNQ’s 1970

TTF-TCNQ first organic metal 1973 Alan Heeger, (not superconductor) others

Rick Greene, (SN)x , first (and only) 1975 polymeric superconductor Tc~0.3K

Bechgaard and Jerome First Organic 1979 Superconductor TMTSF PF Tc~1.2K 2 6

G. Saito, (ET)2Cu[N(CN)2Br] Tc~13K

R R X X Y2 X X Y1 X X

X X X X X X R R Y2 Y1 DBTTF : X=S R R TTF : X=S, R=H DBTSF : X=Se X X TSF : X=Se, R=H ET(BEDT-TTF) : X=Y1=Y2=S TTeF : X=Te, R=H BO(BEDO-TTF) : X=S,Y1=Y2=O X X Wudl TMTSF : X=Se, R=Me BETS(BEDT-TSF) : X=Se,Y1=Y2=S TMTTF : X=S, R=Me EOET : X=S,Y =S,Y =O X X 1 2 X X R R HMTTF : X=S HMTSF : X=Se X X S S S S HMTTeF : X=Te TTF : X=S, R=H Quasi 1D S S X X S S S S S S TSF : X=Se, R=H OMTTF : X=S BPDT-TTF OMTSF : X=Se S S S S TTeF : X=Te, R=H S S S S BVDT-TTF Me Me TMTSF : X=Se, R=Me S S S S Te Te S S TMTTF : X=S, R=Me BMDT-TTF Te Te S S S Me Me S S S S S S BDMT-TTeF BET-TTF S S S XX XC H MDT-TTF H2n+1CnX S S n 2n+1 Y Y R2 R1 2 X X 1 S S H2n+1CnX XCnH2n+1 XX R2 R1 TTCn-TTF : X=S R R XX TSeCn-TTF : X=Se TTeC -TTF : X=Te X X DMTTA : X=S, R1=H, R2=Me n Y Y TMTTA : X=S, R1=R2==Me 2 1 R R S C H 6,7-DMTTA : X=S, R1=H, R2=Me S S n 2n+1 XX TSA : X=Se, R1=R2=H TTN : X=S, R=H DMTSA : X=Se, R1=Me, R2=H S S S CnH2n+1 TSN : X=Se, R=H 6,7-DMTSA : X=Se, R1=H, R2=Me CnTET-TTF ET(BEDT-TTF) : X=Y1=Y2=S TMTTeN : X=Te, R=Me TMTSA : X=Se, R1=R2=Me DMTTeA : X=Te, R1=Me, R2=H BO(BEDO-TTF) : X=S,Y1=Y2=O S S BETS(BEDT-TSF) : X=Se,Y =Y =S XX R1 S 1 2 R R4 R1 2 S EOET : X=S,Y1=S,Y2=O R R 3 2 DTPY : R =R =H YY 1 2 S MSDTPY : R1=SeMe,R2=H S TTT : X=Y=S, R1=R2=R3=R4=H MTDTPY : R =SMe,R =H S 1 2 S Yagubski F2TTT : X=Y=S, R1=R2=R3=R4=H R Quasi 2D 2 Ph2DTPY : R1=Ph,R2=H TST : X=Y=Se, R1=R2=F, R3=R4=H R 3,8-(MeO)2DTPY : R1=H, R2=MeO TTeT : X=Y=Te,R1=R2=R3=R4=H 1 ETDTPY Saito

Me2N NMe2 S Me S S Me2N NMe2 Me N NMe 2 2 S S Me S TMPD TDAE TMDTDM-TTF Superconductivity Discovered by 1911 Gilles Holst

Superconductivity Explained 1957 BCS

Bill Little proposes Excitonic, 1963 Organic, Polymeric Superconductor Schegolev, Bloch, Heeger,…. Fred Wudl discovers TTF Work on “1D” metals, TCNQ’s 1970

TTF-TCNQ first organic metal 1973 Alan Heeger, (not superconductor) others

Rick Greene, (SN)x , first (and only) 1975 polymeric superconductor Tc~0.3K

Bechgaard and Jerome First Organic 1979 Superconductor TMTSF PF Tc~1.2K 2 6

G. Saito, (ET)2Cu[N(CN)2Br] Tc~13K

Observed and hinted at ground states

BEDT-TTF family (TMTSF)2PF6 Supercond – singlet Supercond – triplet? - d-wave? SDW - LOFF? CDW Ferromagnetic Field Induced SDW SDW Quantum Hall CDW Fermi-Liquid Quantum Hall? Non – Fermi, Luttinger? Liq Fermi-Liquid Mott Insulator? Crystal Structure of Bechgaard Salts (TMTSF)2X

• Highly anisotropic -2 -5 σa : σb : σc = 1 : 10 : 10 4t : 4t : 4t = 1 : 0.1: 0.003 (eV) a b c 2 σi ~ ti

• 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 • ¼ Filled, Slightly Dimerized α =°=°=°83.39 ,βγ 86.27 , 71.01 Single chain has charge gap. oo o abc=Α=Α=Α7.297 , 7.711 , 13.522

Kang 30 Woowon 25

)

t (

15 l H a t W 0 e

m = D 10

n S

F 0 H

l a Q t e

l ) a

D r t

c a

e s PF b

k 2

m ( S P 5

S 0 0

15 10 T(K) Phase Diagram (TMTSF) 1D metals are unstable – Fermi Surfaces Nest Interchain hopping – warped Fermi Surface – regain metal Pressure increases interchain hopping – more 3D 30 25

)

t (

15 l H a t W 0 e

m = D 10

n S

F 0 H

l a Q t e

l ) a

D r t

c a

e s

b e

m ( S P k li

5 D W 3

e D

S or 0 0 5

15 10 T(K) M 3D (P,H,T) phase diagram of (TMTSF)2PF6

First guess from g-ology g1

TS SDW

) (SS) K

( g2

T SDW is ax P(kb / c- ar) SC H /

1D-electron gas phase diagram Insulator-Superconductor Bechgaard, Jerome 1979 (“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 Singlet (s,d-wave)?

M.Y. Choi et.al., Phys. Rev. B25, 6208 (1982) P.M. Chaikin, M.Y. Choi and R.L. Greene, Mag. Mat. 31, 1268 (1983) Proton spin-lattice relaxation experiments

M. Takigawa et.al., J.Phys. Soc. Jpn. 56, 873 (1987) T3 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 ⎛ 4t ⎞ ⎜ b ⎟ b = bw ⎜ ⎟ ⎝ Bev zF ⎠ vF y h B λ = z x ebB z

evf bBz ωb = ky h Chaikin, Azbel, Holstein, ‘83 kx But nesting at q=2kF +/- nG, G=2π/λ

Woowon Kang

Integer Quantum Hall Effect in (TMTSF)2PF 6

100 T = 300mK N = 1 P = 10kbar Ω) 50 (m N = 2 xy

R N = 3 N = 4

60 Ω) (m

xx 30 R

0 0 5 10 15 B(tesla) 30

20 i

)

t (

15 1 l H

t W 0 e

m = r

10 D o

n S M

F 0 H

l a Q t e

l ) a

D r t

c a

e s

b e

m ( S P k li

5 D W 3

e D

S or 0 0 5

15 10 T(K) M Main lesson:

Magnetic field perpendicular to the chains reduces electronic dimension

Does this decouple chains/planes?

H=0 c b c b H a

3D coherent Coherent planes Two Contributions to Magnetic Critical Field - Orbital and Spin

Orbital term derives from Field Expulsion Spin derives from susceptibility e.g. Meisner Effect of spin paired state

Need currents to expel field ΔF~ - (1/2)ΔχH2 j~H, ΔF~K.E. ~j2~H2

FNormal FNormal H 2 F c2orbital - (1/2) χPauliH

Fsuper Fsuper H H HPauli

Usually Hc2orbital <

T Tc Note: When μ H > Δ ↑↓> 0 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 t /T = 7 c c a b

tc /Tc = 4 Test for the triplet superconducting pairing?

Δ H p = = c TeslaT ][84.1 2μo

L.I. Burlarchkov, L.P. Gor’kov and A.G. Lebed’ Europhys. Lett., 4 941 (1987)

Injae Lee Junction

6 (TMTSF) PF 2 6 P=6kbar

H // b' 4

Magnetic Field (T) Magnetic Field 2 H // a

1 H // c* 0

0.0 0.3 0.6 0.9 1.2

temperature (K) Injae Lee

2μH 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

1.0 n

χ χ ω − ω = n / 0.5 H // a χ χn Ks Singlet H // b 0.63 H/H = 0 c2 0.0 0.5 1.0 1.5 2.0 T / T (H) P. Fulde and K. Maki, c Phys. Rev. B139, A788 (1965)

(H=2.38T)/(Hc2(0) =5T) ~ 0.5 for H // b I.J. Lee et al., PRL, 88, 17004 (2002) (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

H / π

b 2 k θ c k )/h

k b a 2 / k

π Hbcos(

2 =ev

π 2 / c

rational magic Angles

)/h θ = p/q

c ω / Hbsin(

b F Lebed’s ω =ev c Something happens when ω 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

ky ⊥ Recip space Real space

Quasi-particle coherence

Woowon Kang

xx R

Basic Idea: c Coherent-Incoherent Transition

above Threshold Hperp field

b Strong, Clark, Anderson PRL 73, 1007 (1994) At magic angles metallic 9 ChashechkinaЧашечкина 2L c dR/dT>0 3Max 2L 8 3Max b 1Max At nonmagic angles 7 c* Nonmetallic dR/dT<0 1L 6 -1L 2Max

These differ by 6o Ω ,

zz 4 R

H=0 2

1 c b Similar effect along 0 a,b,c axes 0 5 10 15 20 T , K

Look at Conductivity4 instead of resistivity

3 -100 -50 0 50 100 .1T e

c 2 tan onduc c xis a

c 1 2T

0 9.2T angle (b-c rotation, b=90)

Insulating when decoupled Conducting when field allows interchain tunneling

Angular dependent Nernst Weida Wu

6 2K 4 1K

2 V/K) μ 0 N(

-2 -2L -4 -1L c' 1L

-50 -40 -30 -20 -10 0 10 20 30 40 50 θ Giant Nernst Signal

8 7.5 Tesla 2K Drude, Boltzmann: 1K 6 0.2K N •∝ BTe sinθ 4

kB T 2 ~ cτω

V / K ) e TF μ 0 ( N e ≈ nV /1 K -2

(TMTSF) PF : eVKN ~10μ / -4 -2L 2 6

-6 -1L c' 1L

-8 -40 -20 0 20 40 o θ ( ) Field induced inter-chain decoupling

c' 4 R N 3 5 zz

e 1

θ H H c H c −∇T c c c H a a a a a H 1 2 3 4 5 6.0

4.0

2.0 Transport: V/K )

μ 0.0 Only coherent ( N e -2.0 at planes // H -1 c' +1 -4.0

-6.0 -40 -20 0 20 40 -1 θ c’ +1 b c b c b c a H H H a a

What is the coherence? SC Phase coherence at Magic Angle Planes

c' 4 R N 3 5 zz

e 1

2 θ H H c c c −∇T c −∇T c H H H a a v a a v a 1 2 3 4 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?