Two dimensional magnetism in the layered molecular Mott insulator k-(BEDT-TTF)2 Cu[N(CN)2]Cl

1
Confinement of spin diffusion to single molecular
layers in layered organic conductor crystals
I.F. Schegolev Memorial Conference
Low-Dimensional Metallic and Superconducting
Systems October 1116, 2009, Chernogolovka,
Russia
András Jánossy1 Ágnes Antal1 Titusz Fehér1
Richard Gaál2 Bálint Náfrádi1,2 László
Forró2 Crystal growth Erzsébet Tátrainé
Szekeres1, Ferenc Fülöp1 special thanks
to Natasha Kushch 1Budapest University of
Technology and Economics, Institute of
Physics 2Ecole Polytechnique Federale de Lausanne
2
Quasi 2D molecular layered compounds
Independent currents in each layer? Uncoupled
magnetic order in each layer?
IA or MA
A
IB or MB
B
A
B
3
?- ET2-X, layered organic crystal X
CuN(CN)2Cl, Br 2D polymer
b
1 hole / ET2 dimer
c
A
X
B
a
4
?- ET2-X, layered organic crystal X
CuN(CN)2Cl, Br 2D polymer
b
1 hole / ET2 dimer
c
A
tII
t?
X
B
a
t// ? 100 meV
?ac45
t?? 0.1 meV
5
Phase diagram?-(BEDT-TTF)2CuN(CN)2Cl, Br
Mott transition
6
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
7
High frequency ESR spectrometer high
resolution same sensitivity 0-12 kbar pressure
420 GHz, Lausanne 222.4 GHz, Budapest
9.4 GHz BRUKER E500
8
Phase diagram?-(BEDT-TTF)2CuN(CN)2Cl, Br
ET-Cl
ET-Br
2. Conduction electron spin resonance
1. Antiferromagnetic resonance
9
Antiferromagnetic resonance
F HZeeman Hexchange
HDM Hanisotropy F -
B(M1 M2 ) ? M1 M2 D(M1 x M2)
½Kb(M1y2 M2y2)½K(M1z2 M2z2)
D
z
y
M1
M2
B
2 magnetizations ? 2 oscillation modes
First AFMR work Ohta et al, Synth. Met, 86,
(1997), 2079-2080
10
Magnetic structure
J 600 T
lAB ?
D. F. Smith and C. P. Slichter, Phys. Rev. Let.
93, 167002, 2004
F FA FB lABMAMB
11
Antiferromagnetic resonance calculation
?-(BEDT-TTF)2CuN(CN)2Cl
B // b
F FA FB lABMAMB
4 magnetizations 4 modes ?aA , ?bA ?aB
, ?bA
Antal et al., Phys. Rev. Lett. 102, 086404 (2009)
12
Antiferromagnetic resonance experiment
?-(BEDT-TTF)2CuN(CN)2Cl
AFMR, 111.2 GHz, 4 K, H//b
F FA FB lABMAMB
4 magnetizations 4 modes ?aA , ?bA ?aB
, ?bA
Antal et al., Phys. Rev. Lett. 102, 086404 (2009)
13
Antiferromagnetic resonance measured and
calculated
A
lAB
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)
Antal et al., Phys. Rev. Lett. 102, 086404 (2009)
14
Conduction electron spin resonance in the
metallic phase
ET-Cl
ET-Br
Conduction electron spin resonance
5
1
10
15
2D spin diffusion
?? interlayer hopping rate T1
spin life time ?? lt 1/T1 2D spin
diffusion
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2D spin diffusion
?spin 250 nm
vF?// 1 nm
A
??
t?
B
?? (2t?2 ?//) / h 2 blocked by short ?//
N. Kumar, A. M. Jayannavar, Phys. Rev. B 45,
5001 (1992)
Expectation (300 K) h / t? 10-11 s, ?//
10-14 s T1 10-9 s ??
2x108 s lt 1/T1 2D spin diffusion
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Measurement of interlayer hopping ESR of 2
coupled spins
?A gA?BB/h
A
??
?B gB?BB/h
B
gA ? gB
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Measurement of interlayer hopping
ESR
?? gt I ?A ?B I
?B
?A
interlayer hopping frequency
?? I ?A ?B I
?B
?A
?? lt I ?A ?B I
?B
?A
19
2 resolved ESR lines P0, T45-300 K
?A
?B
A
??
Ref.
B
?? lt I ?A ?B I ?? lt 3 x 108 Hz
Antal et al., Phys. Rev. Lett. 102, 086404 (2009)
20
ESR g- factor anisotropy 45 -250 K
?-(BEDT-TTF)2CuN(CN)2Cl
?B
??
?A

Antal et al., Phys. Rev. Lett. 102, 086404 (2009)
21
Measurement of interlayer hopping
ESR
?? gt I ?A ?B I
?B
?A
interlayer hopping frequency
pressure
?? I ?A ?B I
?B
?A
?? lt I ?A ?B I
?B
?A
22
Measurement of interlayer hopping
Motional narrowing under pressure 210 GHz T250
K, B in (a,b) plane
?-ET2-Cl
Ref.
Instr.
?? gt I ?A ?B I
?? I ?A ?B I
pressure
?? lt I ?A ?B I
23
Measurement of interlayer hopping
Motional narrowing under pressure 420 GHz T250
K,
?A
ESR spectral intensity
?B
?? I ?A ?B I 1.0 x109 s-1
24
Measurement of interlayer hopping
pressure dependence
T250 K
?? (2t?2 ?//)/h2 blocked interlayer
hopping ??? ? ?// parallel d.c. conductivity
25
Summary
??(P, T) interlayer hopping frequency
ET-Cl
ET-Br
2x108 s-1
5x109 s-1
5
1
10
26
Measurement of interlayer hopping
temperature dependence 111.2 GHz P0
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Measurement of interlayer hopping
temperature dependence 111.2 GHz P4 kbar
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2D spin diffusion
?? (2t?2 ?//) / h 2 blocked by short ?//
Measurement 250 K, P0 ?? 2x108 s-1
lt 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
29
Anisotropy of resistivity
t//? 100 meV
t?? 0.1 meV
H. Ito et al J. Phys. Soc. Japan 65 2987 (1996)

• ?? / ?// nearly independent of T
• ?? ? 100 ?cm
• ?? / ?// ? 102 - 103

30
Anisotropy of resistivity
?-(BEDT-TTF)2CuN(CN)2Br
?-(BEDT-TTF)2CuN(CN)2Cl
Buravov et al. J. Phys. I 2 1257(1992)
H. Ito et al J. Phys. Soc. Japan 65 2987 (1996)
?? (2t?2 ?//) / h 2 blocking of interlayer
tunnelling ?? ? 1 / ?? ? 1 / ?// , ?// ? 1
/ ?// ?? / ?// ? ( t// / t ?)2 (a/d)2
independent of T
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Perpendicular dc resistivity     ?? 1/( e2
g(EF) ?? d)     g(EF) two dimensinal density of
states   d interlayer distance ?-(BEDT-TTF)2C
uN(CN)2Cl at 250 K, P0 Calculated ?? 80
-300 ?cm Typical measured 100 ?cm
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Anisotropy of resistivity
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
33
?-(BEDT-TTF)2Mn2Cl5(H2O)5
Mn Layer B
Mn Layer A
Zorina et al CrystEngComm, 2009, 11, 2102
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ESR in (ET)2CuMnN(CN)24, 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)
ESR spectrum in the a direction at 420 GHz and
300 K. Resolved lines correspond to the Mn2
ions and the ET molecules.
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(No Transcript)
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Me-3.5-DIP)Ni(dmit)22 PS3-7 Yamamoto bi
functional conductor PHYSICAL REVIEW B 77,
060403R 2008 PS3-10 Hazama transport under
pressure
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Summary
??(P, T) interlayer hopping frequency
ET-Cl
ET-Br
2x108 s-1
5x109 s-1
5
1
10
38
Antiferromagnet lAB lAB exchange lAB
dipole same order of magnitude Maybe
lAB changes sign at Mott transition ?
lAB
39
Measurement of interlayer hopping
Motional narrowing under pressure 420 GHz T250
K, B in (a,b) plane
?-ET2-Cl
Ref.
Instr.
?? gt I ?A ?B I
?? I ?A ?B I
?? 1 lt I ?A ?B I
40
Antiferromagnetic resonance Calculated B in
(a,b) plane
B
?ab
A
?a
?b
A layers only
41
Antiferromagnetic resonance Calculated B in
(a,b) plane
A
B
Independent A and B layers A and B modes cross!
42
Antiferromagnetic resonance ?-(BEDT-TTF)2CuN(CN)2
Cl
B // b
A. Antal et al 2008 (present work)
Ohta et al, Synth. Met, 86, (1997), 2079-2080
43
?-(BEDT-TTF)2CuN(CN)2Clresistivity
Zverev et al, Phys. Rev. B. 74, 104504 (2006)