Confinement of spin diffusion to single molecular layers in layered organic conductor crystals...

Confinement of spin diffusion to single molecular layers in layered

organic conductor crystals

András Jánossy1

Ágnes Antal1

Titusz Fehér1

Richard Gaál2

Bálint Náfrádi1,2

László Forró2

Crystal growth: Erzsébet Tátrainé Szekeres1, Ferenc Fülöp1

special thanks to Natasha Kushch1Budapest University of Technology and Economics, Institute of Physics2Ecole Polytechnique Federale de Lausanne

I.F. Schegolev Memorial Conference “Low-Dimensional Metallic and Superconducting Systems”

October 11–16, 2009, Chernogolovka, Russia

Quasi 2D molecular layered compounds:

Independent currents in each layer?

Uncoupled magnetic order in each layer?

Aor MA

Bor MB

A

B

A

B

ac=0°

ac=90°

- ET2-X, layered organic crystalX = Cu[N(CN)2]Cl, Br 2D polymer

c

a

b

A

B

1 hole / ET2 dimer

X

c

a

b

A

B

1 hole / ET2 dimer

X

tII

ac=45°

t

t 0.1 meV

t// 100 meV

- ET2-X, layered organic crystalX = Cu[N(CN)2]Cl, Br 2D polymer

0,0 0,1 0,2 0,3 0,4 0,5 0,60

50

100

150

200

250

300

Tem

pera

ture

(K

)

Pressure (kbar)

Antiferromagnet Superconductor

Insulator Metal

"Bad" metal

Phase diagram-(BEDT-TTF)2CuN(CN)2Cl, Br

51 10

Mott transition

Goal:

Determine:

1. interlayer magnetic interaction in antiferromagnet

2. interlayer electron hopping frequency, in metallic phase

Method: high frequency ESR

1. Antiferromagnetic resonance, AFMR

2. Conduction electron spin resonance, CESR

0.33 0.34 0.35 0.36 0.37 0.38

7.96 7.97 7.98 7.99 8.00

Magnetic field (T)

9 GHz

222 GHz

9.4 GHz

BRUKER E500

420 GHz, Lausanne

222.4 GHz, Budapest

High frequency ESR spectrometer

high resolutionsame sensitivity0-12 kbar pressure

7,90 7,95 8,00 8,05

Magnetic field (T)

TEKCL7 ET2CuN(CN)

2Cl (a,b) plane ESR at 222.4GHz

250 K

A B Ref.

0,0 0,1 0,2 0,3 0,4 0,5 0,60

50

100

150

200

250

300

Tem

pera

ture

(K

)

Pressure (kbar)


Insulator Metal

"Bad" metal

Phase diagram-(BEDT-TTF)2CuN(CN)2Cl, Br

ET-Cl ET-Br

2. Conduction electron spin resonance

51 10

1. Antiferromagnetic resonance

D

y

z

BM1 M2

F = HZeeman + Hexchange + HDM + Hanisotropy

F = - B(M1 + M2 ) + M1 M2 + D(M1 x M2) + ½Kb(M1y2 +M2y

2)+½K(M1z2 + M2z

2)

Antiferromagnetic resonance

2 magnetizations 2 oscillation modes

First AFMR work: Ohta et al, Synth. Met, 86, (1997), 2079-2080

DA

MA1

MA2

DB

MB2

MB1

Magnetic structure

D. F. Smith and C. P. Slichter, Phys. Rev. Let. 93, 167002, 2004

A

B

AB =?

J = 600 T

F = FA + FB + ABMAMB

Antiferromagnetic resonancecalculation -(BEDT-TTF)2CuN(CN)2Cl

4 magnetizations : 4 modes:

ωαA , ωA

ωαB , ωA


Antal et al., Phys. Rev. Lett. 102, 086404 (2009)

111.2 GHz

ωω

Magnetic field [T]

Fre

quen

cy [

GH

z]

B // b

Antiferromagnetic resonanceexperiment -(BEDT-TTF)2CuN(CN)2Cl

4 magnetizations : 4 modes:

ωαA , ωA

ωαB , ωA


AFMR, 111.2 GHz, 4 K, H//b


-30 0 30 60 90 120 150 180 210

2

3

4

5

6

7

8

9

-aba

ab

(deg)

Reso

nance

field

(T

)

dB

dA

(a)

A

B

A and B modes do not cross!

intra-layer exchange: J = 600 T

inter-layer coupling: AB =1x 10-3 T

AB = AB exchange + AB dipole (same order of magnitude)

AB

Antiferromagnetic resonancemeasured and calculated

b

a

B, magnetic field

ab


0,0 0,1 0,2 0,3 0,4 0,5 0,60

50

100

150

200

250

300

Tem

pera

ture

(K

)

Pressure (kbar)


Insulator Metal

Metal

ET-Cl ET-Br

Conduction electron spin resonance

51 10

Conduction electron spin resonancein the metallic phase

A

B

2D spin diffusion

interlayer hopping rate

T1 spin life time

< 1/T1 2D spin diffusion

Expectation (300 K) :

ħ / t ≈ 10-11 s,

// ≈ 10-14 s

T1 ≈ 10-9 s

≈ 2x108 s < 1/T1 2D spin diffusion

2D spin diffusion

vF//= 1 nm spin ≈ 250 nmA

B

= (2t2 //) / ħ 2 blocked by short //

N. Kumar, A. M. Jayannavar, Phys. Rev. B 45, 5001 (1992)

t

A

B

A= gABB/h

B= gBBB/h

Measurement of interlayer hopping

ESR of 2 coupled spins

gA ≠ gB

A B

A B

A B

ESR

< I A – B I

≈ I A – B I

> I A – B I


inte

rlaye

r ho

ppin

g fr

eque

ncy

7,90 7,95 8,00 8,05

A. Antal, BUTE, April 2008Magnetic field (T)

TEKCL7 ET2CuN(CN)

2Cl (a,b) plane ESR at 222.4GHz

250 K

BA

2 resolved ESR lines P=0, T=45-300 K

A

B

< I A – B I

< 3 x 108 Hz

Ref.


ESR g- factor anisotropy 45 -250 K

-(BEDT-TTF)2CuN(CN)2Cl

-180 -150 -120 -90 -60 -30 0 30 60

-38

-36

-34

-32

-30

-28

-26

-24

-22

-20

-18

-16

-14

A. Antal, BUTE, 2008

TEKCL7 ET2CuN(CN)

2Cl (a,b) plane 250K 222.4GHz

ES

R s

hift (

mT

)

angle, (o)

b

a A

B

b

a

B, magnetic field


A B

A B

A B

ESR

< I A – B I

≈ I A – B I

> I A – B I


pres

sure

inte

rlaye

r ho

ppin

g fr

eque

ncy

7,42 7,44 7,46 7,48 7,50

0,0

0,1

0,2

0,3

0,4

0,5

Pre

ssur

e (G

Pa)

Magnetic field (T)

experiment7,42 7,44 7,46 7,48 7,50

0,0

0,1

0,2

0,3

0,4

0,5

fit

Magnetic field (T)

-ET2-Cl

< I A – B I

≈ I A – B I

> I A – B I


Ref.

Motional narrowingunder pressure

210 GHz

T=250 K,B in (a,b) plane

Instr.

pres

sure

0 2 4 6 8 10

14,88

14,90

14,92

14,94

14,96

TEKCl8

Mag

netic

fiel

d (T

)

Pressure (kbar)

0

0,2

0,4

0,6

0,8

1,0

B

A



420 GHz

T=250 K,

= I A – B I = 1.0 x109 s-1

ES

R s

pec

tra

l in

ten

sity

0,0 0,5 1,0

1x109

1x1010

inte

rlaye

r ho

ppin

g ra

te, 2

(

Hz)

Pressure (GPa)

100

1000 C

onductivity (Ohm

cm) -1

= (2t2 //)/ħ2 blocked interlayer hopping

// parallel d.c. conductivity

pressure dependence

T=250 K


0,0 0,1 0,2 0,3 0,4 0,5 0,60

50

100

150

200

250

300

Tem

pera

ture

(K

)

Pressure (kbar)


Insulator Metal

Metal

(P, T) interlayer hopping frequency

ET-Cl ET-Br

51 10

2x108 s-1 5x109 s-1

Summary

4,00 4,02 4,04 4,06 4,08 4,10

TEKCL8 ET2CuN(CN)

2Cl 0 kbar B//DM tempdep 111.2 GHz

Magnetic Field (Tesla)

250K

200K

150K

100K

50K


temperature dependence

111.2 GHz

P=0

tem

pera

ture

Inte

rlaye

r ho

ppin

g fr

eque

ncy

antiferromagnet

metal

temperature dependence

111.2 GHz

P=4 kbar


14,90 14,95 15,00

200

250

TEKCL8 ET2CuN(CN)

2Cl 4kbar B//DM tempdep 420 GHz

Magnetic Field (Tesla)

150

100

50

tem

pera

ture

Interlayer hopping frequencymetal

superconductor

Measurement 250 K, P=0 :

≈ 2x108 s-1 < 1/T1 2D spin diffusion

Electrons are confined to single molecular layers in regions of 350 nm radius

// = 10-14 - 10-13 s t = 0.1 meV - 0.03 meV

2D spin diffusion

= (2t2 //) / ħ 2 blocked by short //

vF//= 1 nmA

B

confinement ≈ 350 nm

t 0.1 meV

t// 100 meV

Anisotropy of resistivity

H. Ito et al J. Phys. Soc. Japan65 2987 (1996)

- / // nearly independent of T

- 100 cm

- / // 102 - 103

= (2t2 //) / ħ 2 blocking of interlayer tunnelling

1 / 1 / // , // 1 / //

/ // ( t// / t )2 (a/d)2 independent of T

H. Ito et al J. Phys. Soc. Japan65 2987 (1996)


Buravov et al. J. Phys. I 2 1257(1992)

-(BEDT-TTF)2CuN(CN)2Br-(BEDT-TTF)2CuN(CN)2Cl

Perpendicular dc resistivity: = 1/( e2 g(EF) d) g(EF) = two dimensinal density of states d: interlayer distance

-(BEDT-TTF)2CuN(CN)2Cl at 250 K, P=0:

Calculated: = 80 -300 cm

Typical measured: 100 cm

t 0.1 meV, t// 100 meV

/ // ( t// / t )2 (a/d)2

expected anisotropy: / // 106

measured: / // 102 - 103

: dc resistivity and DoS agree with CESR

// : measured is much less than calculated ?? unsolved


-(BEDT-TTF)2[Mn2Cl5(H2O)5]†

Zorina et al CrystEngComm, 2009, 11, 2102

MnLayer A

MnLayer B

14.80 14.85 14.90 14.95 15.00 15.05

measurement

simulation

MAGNETIC FIELD (T)

ES

R I

NT

EN

SIT

Y (

arb

. u

.)

ET

Mn

Ref. ESR spectrum in the a* direction at 420 GHz and 300 K. Resolved lines correspond to the Mn2+ ions and the ET molecules.

ESR in (ET)2CuMn[N(CN)2]4, a radical cation salt with quasi two dimensional magnetic layers in a three dimensional polymeric structure

K. L. Nagy1, B. Náfrádi2, N. D. Kushch3, E. B. Yagubskii3, Eberhardt Herdtweck4, T. Fehér1, L. F. Kiss5, L. Forró2, A. Jánossy1

Phys. Rev. B (2009)

Me-3.5-DIP)[Ni(dmit)2]2PS3-7 Yamamoto bi functional conductorPHYSICAL REVIEW B 77, 060403R 2008 PS3-10 Hazama transport under pressure

0,0 0,1 0,2 0,3 0,4 0,5 0,60

50

100

150

200

250

300

Tem

pera

ture

(K

)

Pressure (kbar)


Insulator Metal

Metal

(P, T) interlayer hopping frequency

ET-Cl ET-Br

51 10

2x108 s-1 5x109 s-1

Summary

Antiferromagnet

AB = exchange + AB dipole same order of magnitude

Maybe AB changes sign at Mott transition ?

AB

A

B

14,90 14,95 15,00

0,0

0,2

0,4

0,6

0,8

1,0

Pre

ssur

e (G

Pa)

Magnetic field (T)

experiment

14,90 14,95 15,00

0,0

0,2

0,4

0,6

0,8

1,0

fit

Magnetic field (T)

-ET2-Cl

1 < I A – B I

≈ I A – B I

> I A – B I


Ref.


420 GHz

T=250 K,B in (a,b) plane

Instr.

-30 0 30 60 90 120 150 180 210

2

3

4

5

6

7

8

9

A

A

-aba

ab

(deg)

Reso

nance

field

(T

)

dB

AA

dA

Aω

ω

„A” layers only

B

ab

Antiferromagnetic resonanceCalculated

B in (a,b) plane

-30 0 30 60 90 120 150 180 210

2

3

4

5

6

7

8

9

B A

B A

-aba

ab

(deg)

Reso

nance

field

(T

)

dB

BBAA

dA

A

B

Independent A and B layersA and B modes cross!

Antiferromagnetic resonanceCalculated

B in (a,b) plane

Ohta et al, Synth. Met, 86, (1997), 2079-2080

Antiferromagnetic resonance -(BEDT-TTF)2CuN(CN)2Cl

A. Antal et al 2008 (present work)

B // b

’-(BEDT-TTF)2CuN(CN)2Clresistivity

Zverev et al, Phys. Rev. B. 74, 104504 (2006)

0 50 100 150 200 2500

400

800

1200

0

2

4

6

8

10

12

14

16

18

Res

isti

vity

an

izo

tro

py,

b/

ac

Temperature (K)

b

ac

x400

b/

ac

(

Oh

m·c

m)

Confinement of spin diffusion to single molecular layers in layered organic conductor crystals...

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