ECRYS 2011 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

Outline 1.Anomalies at ~50K in the CDW conductor K 0.30 MoO 3 2.Ultrasonic properties of Rb 0.30 MoO 3, K 0.30 MoO 3 Velocities of longitudinal modes Ultrasonic Attenuation Role of disorder : Rb 0.30 Mo 1-x V x O 3 3. CDW glassy behavior 4. Conclusion

J.P. Pouget et al. K 0.30 MoO 3 Quasi-1D conductor; T p = 180K Chains along b (a,c) plane

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

Temperature dependence of the threshold fields Et 1, Et 2 Two different regimes: T > 50K : Et 1 ≈ 0.1V/cm: Strong damping T < 50K : Et 2 ≈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). TpTp T>50K:Deformable CDW T<50K: Rigid CDW

Proton channeling at low temperature Proton Beam perpendicular to cleavage plane: Backscattering yield X min 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)

Mingliang Tian et al. Phys. Rev. B (2000) Lattice parameters T(K) Noticeable change T ~ 50K Interlayer distance d [-201] chain axis

Normalized thermal expansion along [102]along the transverse direction [-201]  L/L 4K <0 below 50K  L/L 4K [-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)

J. Dumas, B. Layadi et al. Phys. Rev. B (1989) Ratio of the Mo 5+ (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

D. Staresinic et al. Phys. Rev. B (2004) Dielectric spectroscopy Glassy behavior for the CDW at low temperature 50K

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 T p along [102]. Pronounced stiffening below ~50K. //b Platelets 5x4x2mm 3 V = ( C/  

Velocity of the longitudinal mode along [102] and attenuation Anharmonic contribution Attenuation  : Additional contribution T<50K Disorder in CDW superlattice Arrhenius law:  =  0 exp(325/T)  0 = s  V/V = -AT Linear term T<20K:  V/V= -AT. « Bellessa effect », common feature of glasses. 

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.

Longitudinal mode along the transverse direction [-201] Anharmonic contribution  =  0 exp(325/T)  0 = s same activation energy E a =325K : low temperature  - relaxational process in dielectric measurements (D. Staresinic et al.) 

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 E a = 325K at 15 MHz E a = 360K at 1MHz 

K 0.30 MoO 3 : Relative change of the sound velocity : Longitudinal mode along [-201] Similar activated behavior near 50K. E a = 325K [-201] The alkaline element K/Rb plays no important role in the anomaly.  J. De Boer (100K) KRb A (Å) b c 

Role of disorder : Rb 0.30 (Mo 1-x V x ) O 3 x = 0.4 at % Relative change of the velocity of the longitudinal mode propagating along [102] direction. ● V, non isoelectronic impurity; substitution V 5+ / Mo 6+. 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 E a ~ 500K 15 MHz

Rb 0.30 (Mo 1-x V x )O 3 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.

Vogel-Fulcher empirical law :  =  0 exp[ U/(T-T 0 ] ; T>T 0 glass - like behaviour Average activation energy U = 220K Freezing temperature T 0 = 16K our results Thermoelectric power, Kriza et al. (  ) K. Biljakovic et al. Dynamic effect rather than thermodynamic phase transition  = 1 Vogel-Fulcher law

Rb 0.3 MoO 3 Longitudinal sound velocities and elastic constants T=300K Along b5300m/sC 22 = 1.2x10 11 N/m 2 Along [102] 4800 m/sC // = Along [-201]3300m/sC  = 4.6x10 10 Velocities comparable to those of K 0.3 MoO 3 M. Saint-Paul, G.X. Tessema (1989) Water: 1480m/s ; Pb: 1960m/s; Cu: 5010m/s

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 Rb 0.30 Mo 1-x V x O 3 shifted towards higher temp. -Dynamic effect rather than thermodynamic transition -Consistent with CDW glassy-like state

Normalized thermal expansion along [102]  L/L 4K < 0 below ~ 50K

Normalized thermal expansion along the transverse direction [-201]  L/L 4K two times larger than that along the layers [102].  L/L 4K < 0 below ~50K. Anharmonic phonon dynamics.  n < 0 for some low energy modes

Thermal expansion coefficient along [102]

Attenuation Shear mode Wave Amplitude Echogram [-201] Large attenuation on the plateau

Thermal history : Shear mode along [-201], transverse direction

smecticnematic attenuation Analogy with smectic - nematic transition ? F. Kiry, P. Martinoty, J. Phys. 1978

Magnetic susceptibility B.T. Collins, K.V. Ramanujachary, M. Greenblatt, Solid State Comm. 56, 1023 (1985). Tl0.3MoO3K0.3MoO3 L.F. Schneemeyer, F.J. DiSalvo, R.M. Fleming, J.V. Waszczak, J. Solid State Chem. 54, 358 (1984)

Order Parameter J.P. Pouget et al. (1985)

Thermally stimulated depolarization current R.J. Cava, R.M. Fleming et al., Phys. Rev. Lett (1984).

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B. Zawilski et al. Solid State Comm. 124, 395 (2002)