Transcript Two dimensional magnetism in the layered molecular Mott

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 11–16, 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
Quasi 2D molecular layered compounds:
Independent currents in each layer?
Uncoupled magnetic order in each layer?
A
IA or MA
B
IB or MB
A
B
- ET2-X, layered organic crystal
X = Cu[N(CN)2]Cl, Br 2D polymer
c
b
1 hole / ET2 dimer
A
ac=90°
X
ac=0°
a
B
- ET2-X, layered organic crystal
X = Cu[N(CN)2]Cl, Br 2D polymer
c
b
1 hole / ET2 dimer
A
tII
t
X
B
a
t//  100 meV
t 0.1 meV
ac=45°
Phase diagram
-(BEDT-TTF)2CuN(CN)2Cl, Br
300
Temperature (K)
250
"Bad" metal
200
150
Mott
transition
100
50
0
0,0
Metal
Insulator
Antiferromagnet
0,1
0,2
Superconductor
0,3
0,4
Pressure (kbar)
0,5
0,6
1
5
10
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
High frequency ESR spectrometer
high resolution
same sensitivity
0-12 kbar pressure
TEKCL7 ET2CuN(CN)2Cl (a,b) plane ESR at 222.4GHz
250 K
420 GHz, Lausanne
222.4 GHz, Budapest
A
7,90
B
7,95
Ref.
8,00
8,05
Magnetic field (T)
9.4 GHz
BRUKER E500
7.96
7.97
7.98
7.99
8.00
222 GHz
9 GHz
0.33
0.34
0.35
0.36
0.37
Magnetic field (T)
0.38
Phase diagram
-(BEDT-TTF)2CuN(CN)2Cl, Br
ET-Cl
ET-Br
300
2. Conduction electron spin resonance
Temperature (K)
250
"Bad" metal
200
150
100
50
0
0,0
Metal
Insulator
Antiferromagnet
1. Antiferromagnetic
resonance
0,1
0,2
Superconductor
0,3
0,4
Pressure (kbar)
0,5
0,6
1
5
10
Antiferromagnetic resonance
F=
HZeeman
+
Hexchange +
F = - B(M1 + M2 ) +  M1 M2
HDM
+ D(M1 x M2)
+
Hanisotropy
+ ½Kb(M1y2 +M2y2)+½K(M1z2 + M2z2)
D
z
y
M1
B
M2
2 magnetizations  2 oscillation modes
First AFMR work:
Ohta et al, Synth. Met, 86, (1997), 2079-2080
Magnetic structure
DA
J = 600 T
MA1
A
MA2
AB =?
DB
MB2
B
MB1
D. F. Smith and C. P. Slichter, Phys. Rev. Let. 93, 167002, 2004
F = FA + FB + ABMAMB
Antiferromagnetic resonance
calculation
-(BEDT-TTF)2CuN(CN)2Cl
F = FA + FB + ABMAMB
4 magnetizations : 4 modes:
ωαA , ωbA
Frequency [GHz]
B // b
ωb
ωa
111.2 GHz
ωαB , ωbA
Magnetic field [T]
Antal et al., Phys. Rev. Lett. 102, 086404 (2009)
Antiferromagnetic resonance
experiment
-(BEDT-TTF)2CuN(CN)2Cl
AFMR, 111.2 GHz, 4 K, H//b
F = FA + FB + ABMAMB
4 magnetizations : 4 modes:
ωαA , ωbA
ωαB , ωbA
Antal et al., Phys. Rev. Lett. 102, 086404 (2009)
b
Antiferromagnetic resonance
measured and calculated
a
Resonance field (T)
9
dA
B, magnetic field
b
dB
ab
-a
a
(a)
8
7
AB
6
A
5
4
B
3
2
-30
0
30
60
90
120
150
180
210
ab (deg)
A and B modes do not cross!
intra-layer exchange:
inter-layer coupling:
J = 600 T
AB =1x 10-3 T
 AB =  AB exchange +  AB dipole
(same order of magnitude)
Antal et al., Phys. Rev. Lett. 102, 086404 (2009)
Conduction electron spin resonance
in the metallic phase
ET-Cl
ET-Br
300
Conduction electron spin resonance
Temperature (K)
250
Metal
200
150
100
50
0
0,0
Metal
Insulator
Antiferromagnet
0,1
0,2
Superconductor
0,3
0,4
Pressure (kbar)
0,5
0,6
1
5
10
2D spin diffusion
A

B

interlayer hopping rate
T1
spin life time
 < 1/T1
2D spin diffusion
2D spin diffusion
spin ≈ 250 nm
vF//= 1 nm
t
 = (2t2 //) / ħ 2
A

B
blocked by short //
N. Kumar, A. M. Jayannavar, Phys. Rev. B 45, 5001 (1992)
Expectation (300 K) :
ħ / t ≈ 10-11 s,
// ≈ 10-14 s
T1 ≈ 10-9 s
 ≈ 2x108 s
< 1/T1
2D spin diffusion
Measurement of interlayer hopping
ESR of 2 coupled spins
A= gABB/h
A

B
B= gBBB/h
gA ≠ gB
Measurement of interlayer hopping
ESR
A
A
B
B
 ≈ I A – B I
 < I A – B I
A
B
interlayer hopping frequency
 > I A – B I
2 resolved ESR lines
P=0, T=45-300 K
TEKCL7 ET2CuN(CN)2Cl (a,b) plane ESR at 222.4GHz
250 K
A
B
A

Ref.
B
7,90
7,95
8,00
Magnetic field (T)
8,05
A. Antal, BUTE, April 2008
 < I A – B I
 < 3 x 108 Hz
Antal et al., Phys. Rev. Lett. 102, 086404 (2009)
ESR g- factor anisotropy
45 -250 K
b
-(BEDT-TTF)2CuN(CN)2Cl
B, magnetic field
a
TEKCL7 ET2CuN(CN)2Cl (a,b) plane 250K 222.4GHz
-14
-16
-18
ESR shift (mT)
-20
b
-22
B
-24
-26
-28
-30
-32
A
a
-34
-36
-38
-180
-150
-120
-90
-60
-30
o
angle, a ( )
Antal et al., Phys. Rev. Lett. 102, 086404 (2009)
0
30
60
A. Antal, BUTE, 2008

a
Measurement of interlayer hopping
ESR
A
B
B
 ≈ I A – B I
 < I A – B I
A
B
pressure
A
interlayer hopping frequency
 > I A – B I
Measurement of interlayer hopping
Motional narrowing
under pressure
-ET2-Cl
210 GHz
0,5
T=250 K,
B in (a,b) plane
0,5
Ref.
0,4
0,4
0,3
0,3
0,2
0,2
 > I A – B I
 ≈ I A – B I
0,1
0,1
0,0
0,0
experiment
7,42
7,44
7,46
fit
7,48
7,50
Magnetic field (T)
7,42
7,44
7,46
7,48
7,50
Magnetic field (T)
 < I A – B I
pressure
Pressure (GPa)
Instr.
Measurement of interlayer hopping
Motional narrowing
under pressure
420 GHz
TEKCl8
A
B
Magnetic field (T)
14,94
1,0
0,8
14,92
0,6
0,4
14,90
0,2
0
14,88
0
2
4
6
8
Pressure (kbar)
 = I A – B I = 1.0 x109 s-1
10
ESR spectral intensity
14,96
T=250 K,
Measurement of interlayer hopping
pressure dependence
T=250 K
10
1x10


100
9
1x10
Conductivity (Ohm cm)
-1
interlayer hopping rate, 2 (Hz)
1000
0,0
0,5
1,0
Pressure (GPa)
= (2t2 //)/ħ2
blocked interlayer hopping
  //
parallel d.c. conductivity
Summary
(P, T) interlayer hopping frequency
ET-Cl
ET-Br
300
Temperature (K)
250
2x108 s-1
5x109 s-1
Metal
200
150
100
50
0
0,0
Metal
Insulator
Antiferromagnet
0,1
0,2
Superconductor
0,3
0,4
Pressure (kbar)
0,5
0,6
1
5
10
Measurement of interlayer hopping
temperature dependence
metal
111.2 GHz
TEKCL8 ET2CuN(CN)2Cl 0 kbar B//DM tempdep 111.2 GHz
P=0
200K
temperature
150K
100K
50K
4,00
4,02
4,04
4,06
Magnetic Field (Tesla)
4,08
4,10
Interlayer hopping frequency
250K
antiferromagnet
Measurement of interlayer hopping
temperature dependence
metal
111.2 GHz
TEKCL8 ET2CuN(CN)2Cl 4kbar B//DM tempdep 420 GHz
P=4 kbar
250
temperature
150
100
50
14,90
14,95
Interlayer hopping frequency
200
15,00
Magnetic Field (Tesla)
superconductor
2D spin diffusion
confinement ≈ 350 nm
vF//= 1 nm
A

B
 = (2t2 //) / ħ 2
blocked by short //
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
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
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 //) / ħ 2 blocking of interlayer tunnelling
  1 /   1 / // ,
//  1 / //
 / //  ( t// / t )2 (a/d)2
independent of T
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
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
a-(BEDT-TTF)2[Mn2Cl5(H2O)5]†
Mn
Layer A
Mn
Layer B
Zorina et al CrystEngComm, 2009, 11, 2102
ESR INTENSITY (arb. u.)
ESR in (ET)2CuMn[N(CN)2]4,
a radical cation salt with
quasi two dimensional magnetic layers
in a three dimensional polymeric structure
Mn
ET
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)
measurement
simulation
Ref.
14.80
14.85
14.90
14.95
MAGNETIC FIELD (T)
15.00
15.05
ESR spectrum in the a* direction at 420 GHz and 300 K.
Resolved lines correspond to the Mn2+ ions and the ET molecules.
Me-3.5-DIP)[Ni(dmit)2]2
PS3-7 Yamamoto bi functional conductor
PHYSICAL REVIEW B 77, 060403R 2008
PS3-10 Hazama transport under pressure
Summary
(P, T) interlayer hopping frequency
ET-Cl
ET-Br
300
Temperature (K)
250
2x108 s-1
5x109 s-1
Metal
200
150
100
50
0
0,0
Metal
Insulator
Antiferromagnet
0,1
0,2
Superconductor
0,3
0,4
Pressure (kbar)
0,5
0,6
1
5
10
Antiferromagnet
AB = AB exchange + AB dipole
same order of magnitude
Maybe AB changes sign at Mott transition ?
A
AB
B
Measurement of interlayer hopping
Motional narrowing
under pressure
-ET2-Cl
420 GHz
Instr. Ref.
Pressure (GPa)
T=250 K,
B in (a,b) plane
1,0
1,0
0,8
0,8
0,6
0,6
0,4
0,4
 > I A – B I
 ≈ I A – B I
0,2
0,2
0,0
0,0
experiment
14,90
fit
14,95
15,00
Magnetic field (T)
14,90
14,95
15,00
Magnetic field (T)
 1 < I A – B I
Antiferromagnetic resonance
Calculated
B
B in (a,b) plane
a
dA
b
dB
ab
-a
Resonance field (T)
9
8
A
A
7
6
5
A
4
ωb
3
A
2
-30
A
ωa
0
30
60
90
120
150
ab (deg)
„A” layers only
180
210
Antiferromagnetic resonance
Calculated
B in (a,b) plane
a
dA
b
-a
dB
Resonance field (T)
9
8
A
7
A
A
B
B
6
5
4
B
A
B
A
3
2
-30
0
30
60
90
120
150
180
ab (deg)
Independent A and B layers
A and B modes cross!
210
B
Antiferromagnetic resonance
-(BEDT-TTF)2CuN(CN)2Cl
A. Antal et al 2008 (present work)
Ohta et al, Synth. Met, 86, (1997), 2079-2080
B // b
’-(BEDT-TTF)2CuN(CN)2Cl
resistivity
18
16
14
b
12
800
10
ac x400
8
6
b/ac
400
4
2
0
0
0
50
100
150
200
Temperature (K)
Zverev et al, Phys. Rev. B. 74, 104504 (2006)
250
 (Ohm·cm)
Resistivity anizotropy, b/ac
1200