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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. ECRYS 2011. Outline Anomalies at ~50K in the CDW conductor K 0.30 MoO 3

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ECRYS 2011

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  1. 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. Marcus Institut Néel, CNRS/UJF, Grenoble, France ECRYS 2011

  2. Outline • Anomalies at ~50K in the CDW conductor K0.30MoO3 • 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

  3. K0.30MoO3 Quasi-1D conductor; Tp = 180K J.P. Pouget et al. Chains along b (a,c) plane

  4. 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

  5. Temperature dependence of the threshold fields Et1, Et2 T>50K:Deformable CDW T<50K: Rigid CDW Tp 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).

  6. 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)

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

  8. Normalized thermal expansion G. Remenyi, J. Dumas (2009) along [102] along the transverse direction [-201] DL/L4K<0 below 50K DL/L4K [-201] larger than that along the layers [102] -Change in phason behaviournear 40K: S. Ravy et al., Phys. Rev. B (2004)

  9. Ratio of the Mo5+ (S=1/2) EPR lines intensities: slow cooling / fast cooling probe the CDW state through interaction between the defects and the CDW modulation Role of the cooling rate: Rapid change of relative EPR intensities near 50K. No effect on V-doped samples Measuring Temperature J. Dumas, B. Layadi et al. Phys. Rev. B (1989)

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

  11. Relative change of the velocity of the longitudinal modes (15MHz) propagating along b, [102], [-201] directions //b Large increase of the velocity below ~50K in the three directions. Pronounced softening at Tp along [102]. Pronounced stiffening below ~50K. V = (C/r) 1/ 2 Platelets 5x4x2mm3

  12. Velocity of the longitudinal mode along [102] and attenuation DV/V = -AT Anharmonic contribution a Arrhenius law: t= t0exp(325/T) t0 =10 -11 s Attenuation a : Additional contribution T<50K Disorder in CDW superlattice Linear term T<20K: DV/V= -AT. « Bellessa effect », common feature of glasses.

  13. Bellessa effect DV/V = - AT ( , ) our results A Nava et al. Amorphous and disordered materials; Bellessa et al. PRL (1978); Nava et al. PRB (1994).

  14. Longitudinal mode along the transverse direction [-201] t= t0 exp(325/T) t0 =10 -11 s same activation energy Ea=325K : low temperature b-relaxational process in dielectric measurements (D. Staresinic et al.) Anharmonic contribution a

  15. Velocity of the longitudinal mode along [102] at 15MHz and 1MHz Frequency dependent anomaly Relative change in velocity and Plateau in the attenuation shifted to lower T when the frequency is decreased. a Ea = 325K at 15 MHz Ea = 360K at 1MHz

  16. K0.30MoO3: Relative change of the sound velocity : Longitudinal mode along [-201] Similar activated behavior near 50K. Ea= 325K [-201] The alkaline element K/Rb plays no important role in the anomaly. a

  17. 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). DV/V=-AT Ea ~ 500K Smearing out of the anomaly and shift towards higher temperature ~70K Anharmonic contribution 15 MHz

  18. 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.

  19. Vogel-Fulcher empirical law : t = t0exp[ U/(T-T0 ] ; T>T0 glass - like behaviour Average activation energy U = 220K Freezing temperature T0 = 16K Vogel-Fulcher law our results (e) K. Biljakovic et al. Dynamic effect rather than thermodynamic phase transition Thermoelectric power , Kriza etal. wt = 1

  20. 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

  21. 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

  22. Normalized thermal expansion along [102] DL/L4K < 0 below ~ 50K

  23. Normalized thermal expansion along the transverse direction [-201] DL/L4K two times larger than that along the layers [102]. DL/L4K < 0below ~50K. Anharmonic phonon dynamics. gn < 0 for some low energy modes

  24. Thermal expansion coefficient along [102]

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

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

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

  28. Magnetic susceptibility Tl0.3MoO3 K0.3MoO3 L.F. Schneemeyer, F.J. DiSalvo, R.M. Fleming, J.V. Waszczak, J. Solid State Chem. 54, 358 (1984) B.T. Collins, K.V. Ramanujachary, M. Greenblatt, Solid State Comm. 56, 1023 (1985).

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

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

  31. F.Nad et al., ECRY93. J. Phys. IV C2, Vol.3, 343 (1993).

  32. J. Yang, N.P. Ong, Phys. Rev. B (1991)

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

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