ecrys 2011
DESCRIPTION
Anomalous behavior of ultrasonic properties near 50K in A 0.30 MoO 3 (A=K, Rb) and Rb 0.30 (Mo 1-x V x )O 3 M. Saint-Paul, J. Dumas, J. Marcus Institut Néel, CNRS/UJF, Grenoble, France. ECRYS 2011. Outline Anomalies at ~50K in the CDW conductor K 0.30 MoO 3 - PowerPoint PPT PresentationTRANSCRIPT
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ECRYS 2011
Anomalous behavior of ultrasonic
properties near 50K in A0.30MoO3
(A=K, Rb) and Rb0.30(Mo1-xVx)O3
M. Saint-Paul, J. Dumas, J. MarcusInstitut Néel, CNRS/UJF, Grenoble, France
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Outline
1. Anomalies at ~50K in the CDW conductor K0.30MoO3
2. Ultrasonic properties of Rb0.30MoO3, K0.30MoO3
Velocities of longitudinal modes
Ultrasonic Attenuation
Role of disorder : Rb0.30Mo1-xVxO3
3. CDW glassy behavior
4. Conclusion
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J.P. Pouget et al.
K0.30MoO3 Quasi-1D conductor; Tp = 180K
Chains along b (a,c) plane
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Nonlinear conductivity at low temperature
• Large and abrupt threshold field at low T.• Very low damping due to freezing of
normal carriers
• T < 50K• Rigid CDW in the low temperature• Insulating state
• G.X. Tessema, L. Mihaly, (1987)• G. Mihaly, P. Beauchêne et al., (1988)
G. Mihaly, P. Beauchêne
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Temperature dependence of the threshold fields Et1, Et2
Two different regimes: T > 50K : Et1 ≈ 0.1V/cm: Strong damping T < 50K : Et2 ≈10 V/cm: Low damping
P. Beauchêne, G. Mihaly et al. (1988); J. Dumas, C. Schlenker (1993).
H. Li, J. Wang et al., Mod. Phys. Lett. B 18, 697 (2004).
Tp
T>50K:Deformable CDW
T<50K: Rigid CDW
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Proton channeling at low temperature
Proton Beam perpendicular to cleavage plane:
Backscattering yield Xmin increases below 40K.
No effect for beam // [102] direction and perp. b
(in the cleavage plane)
Structural Disorder at low T.
CDW defects
B. Daudin, J. Dumas et al., Synth. Metals (1989)
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Mingliang Tian et al. Phys. Rev. B (2000)
Lattice parameters
T(K)
Noticeable change T ~ 50K
Interlayer distance d [-201]
chain axis
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-0.5
0
0.5
1
1.5
2
2.5
3
0 50 100 150 200 250T (K)
[102]
Tp
-0.1
0
0.1
0.2
0.3
0.4
0.5
0 20 40 60 80 100
L/L
4K (
10-3
)
T (K)
Normalized thermal expansion
along [102] along the transverse direction [-201]
L/L4K <0 below 50K L/L4K [-201] larger than that along the layers [102]
G. Remenyi, J. Dumas (2009)
-Change in phason behaviour near 40K: S. Ravy et al., Phys. Rev. B (2004)
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J. Dumas, B. Layadi et al. Phys. Rev. B (1989)
Ratio of the Mo5+ (S=1/2) EPR lines intensities:
slow cooling / fast cooling
Role of the cooling rate: Rapid change of relative EPR intensities near 50K.
No effect on V-doped samples
probe the CDW state through interaction between the defects and the CDW modulation
Measuring Temperature
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D. Staresinic et al. Phys. Rev. B (2004)
Dielectric spectroscopy
Glassy behavior for
the CDW
at low temperature
50K
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Relative change of the velocity of the longitudinal modes (15MHz) propagating along b, [102], [-201] directions
Large increase of the velocity below ~50K in the three directions.
Pronounced softening at Tp along [102].
Pronounced stiffening below ~50K.
//b
Platelets 5x4x2mm3
-0.1
-0.08
-0.06
-0.04
-0.02
0
0 50 100 150 200 250
TP
T (K)
[010]
[102]
[-201]
Rb0.3
MoO3
V = (C/
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-0.04
-0.03
-0.02
-0.01
0
0.01
-5
0
5
10
15
0 20 40 60 80 100
[102]
T (K)
(a)
(b)
Velocity of the longitudinal mode along [102] and attenuation
Anharmonic contribution
Attenuation :
Additional contribution T<50K Disorder in CDW superlattice
TV
TC
V
V2
0
2
2
)(
2
2
)(1
)(
2
)(
R
Ru
V
VV
V
V
2
2
2 )(1
)(
4
1
R
Ru
V
VV
Arrhenius law:
= 0exp(325/T) 0 =10 -11 s
V/V = -AT
Linear term T<20K: V/V= -AT. « Bellessa effect », common feature of glasses.
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A
Bellessa effect V/V = - AT
Amorphous and disordered materials; Bellessa et al. PRL (1978); Nava et al. PRB (1994).
( , ) our results
Nava et al.
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-0.04
-0.03
-0.02
-0.01
0
0.01
0
1
2
3
4
5
6
7
0 20 40 60 80 100
T (K)
[-201]
Longitudinal mode along the transverse direction [-201]
Anharmonic contribution
= 0 exp(325/T)0 =10 -11 ssame activation energy
Ea=325K : low temperature -relaxational process in dielectric measurements
(D. Staresinic et al.)
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-0.015
-0.01
-0.005
0
0.005
0.01
-5
0
5
10
15
20
10 20 30 40 50 60 70T (K)
15MHz
1MHz
15MHz
1MHz
[102] Relative change in velocity and Plateau in the attenuation shifted to lower T when the frequency is decreased.
Velocity of the longitudinal mode along [102] at 15MHz and 1MHz
Frequency dependent anomaly
Ea = 325K at 15 MHz
Ea = 360K at 1MHz
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K0.30MoO3:
Relative change of the sound velocity : Longitudinal mode along [-201]
Similar activated behavior near 50K.
Ea= 325K
-0.02
-0.015
-0.01
-0.005
0
0.005
0
5
10
15
0 50 100 150 200
T (K)
K0.3
MoO3
[-201]
The alkaline element K/Rb plays no important role in the anomaly.
J. De Boer (100K)
K Rb
A (Å) 18.162 18.536
b 7.554 7.556
c 9.816 10.035
117.3 118.5
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-0.015
-0.01
-0.005
0
0.005
0.01
0 20 40 60 80 100
T (K)
[102]
(a)
(b)
Role of disorder : Rb0.30 (Mo1-x Vx) O3 x = 0.4 at %Relative change of the velocity of the longitudinal mode propagating along [102] direction.
● V, non isoelectronic impurity; substitution V5+ / Mo6+. Strong pinning centers. Short range CDW order.
S. Ravy et al., Phys. Rev. B (2006).
Smearing out of the anomaly and shift towards higher temperature ~70K
V/V=-AT
Anharmonic contribution
Ea ~ 500K
15 MHz
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-0.01
-0.005
0
0.005
0 20 40 60 80 100T (K)
(a)
(b)
Ea=500K
Ea= 330K
[-201]
Rb0.30 (Mo1-x Vx)O3 x = 0.4 at % along the transverse direction [-201]
Smearing out of the anomaly and shift towards higher temperature.
Smaller size of domains of coherence of the CDW.
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Vogel-Fulcher empirical law : = 0exp[ U/(T-T0 ] ; T>T0
glass - like behaviour
Average activation energy U = 220K
Freezing temperature
T0 = 16K
our results
Thermoelectric power , Kriza et al.
() K. Biljakovic
et al.
Dynamic effect rather than thermodynamic phase transition
= 1
Vogel-Fulcher law
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Rb0.3MoO3 Longitudinal sound velocities and elastic constants
T=300K
Along b 5300m/s C22 = 1.2x1011 N/m2
Along [102] 4800 m/s C// = 1011
Along [-201] 3300m/s C = 4.6x1010
Velocities comparable to those of K0.3MoO3
M. Saint-Paul, G.X. Tessema (1989)
Water: 1480m/s ; Pb: 1960m/s; Cu: 5010m/s
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Conclusions
-Large elastic anomalies at T~50K along b, [102], [-201] :
-Stiffening of longitudinal waves T<50K, along b, [102], [-201]
-Linear term T<30K
-Increase of the attenuation T ~ 50K followed by a plateau
-Anomaly in Rb0.30 Mo1-xVxO3 shifted towards higher temp.
-Dynamic effect rather than thermodynamic transition
-Consistent with CDW glassy-like state
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-0.5
0
0.5
1
1.5
2
2.5
3
0 50 100 150 200 250T (K)
[102]
Tp
-0.1
0
0.1
0.2
0.3
0.4
0.5
0 20 40 60 80 100
L/L
4K (
10-3
)
T (K)
Normalized thermal expansion along [102]
L/L4K < 0 below ~ 50K
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Normalized thermal expansion along the
transverse direction [-201]
L/L4K
two times larger than that along the layers [102].
L/L4K < 0 below ~50K.
Anharmonic phonon dynamics.
n < 0 for some low energy modes
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-0.5
0
0.5
1
1.5
2
2.5
3
3.5
0 50 100 150 200 250
T (K)
[102]
Thermal expansion coefficient along [102]
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-0.02
-0.01
0
0.01
0.02
0.03
0 25 50 75 100
V/V
T (K)
Attenuation Shear mode W
ave
Am
pli
tud
e
Echogram
[-201]
Large attenuation on the plateau
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Thermal history : Shear mode along [-201], transverse direction
-0.02
-0.01
0
0.01
0.02
0.03
0 25 50 75 100
T (K)
[-201]
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smectic nematic
atte
nu
atio
n
Analogy with smectic - nematic transition ?
F. Kiry, P. Martinoty, J. Phys. 1978
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Magnetic susceptibility
B.T. Collins, K.V. Ramanujachary, M. Greenblatt,
Solid State Comm. 56, 1023 (1985).
Tl0.3MoO3 K0.3MoO3
L.F. Schneemeyer, F.J. DiSalvo, R.M. Fleming, J.V. Waszczak, J. Solid State Chem. 54, 358 (1984)
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Order Parameter
J.P. Pouget et al. (1985)
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Thermally stimulated depolarization current
R.J. Cava, R.M. Fleming et al., Phys. Rev. Lett (1984).
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F.Nad et al., ECRY93. J. Phys. IV C2, Vol.3, 343 (1993).
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J. Yang, N.P. Ong, Phys. Rev. B (1991)
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B. Zawilski et al. Solid State Comm. 124, 395 (2002)