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Study of the charge density wave depinning in K0.3MoO3 by proton dechanneling
Synthetic Metals, 41-43 (1991) 3875
3875
STUDY OF THE CHARGE DENSITY WAVE DEPINNING IN K0.3MoO 3 BY PROTON DECHANNELING
B. Daudin and M. Dubus C E N G - D R F - G / S B T - B P 85 X, 38041 Grenoble Codex, France. J. Dumas CNRS-Laboratoire d~Etudes des Propri~t6s Electroniques des Solides B.P. 166, 38042 Grenoble Cedex, France.
The blue bronze K0.3MoO3 shows a Peierls transition at 180 K towards an incommensurate semiconducting charge density wave (CDW) state. Non linear transport properties associated with the sliding motion of the CDW when the applied electric field exceeds a depinning threshold E t ha~been studied in details (1). Two different regimes of CDW conduction have been reported. Above 40 K, the onset of CDW sliding takes place at small threshold fields (Etl N 10 mV/cm) with a strong damping due to normal carriers. Below 40 K, large threshold values Et2 - 100 Etl are found together with an unusually low damping related to the nearly complete freezing out of the normal carriers. We have investigated the low temperature CDW state by proton dechanneling. The minimum backscattering yield Xmin increases dramatically below 40 K when the sample is cooled slowly from room temperature. No anomaly below 40 K is found after fast cooling, However, in the latter case, Xmin measured at 5 K is found to be strongly time dependent with time scales of the order of one hour. Negligible time dependence is found at - 50 K. In the explored temperature range 4 K < T < 50 K, when an electric field larger than threshold is applied after relaxation of Xmin, an increase of Xmin is observed. As an increase of Xmin always indicate an increase of the structural disorder, the large change in Xmin induced thermally or electrically reflects rearrangements of CDW structural defects. The abrupt change near 40 K in the time scales involved in these experiments may reflect a change m the domain structure. We suggest t h ~ a rotation of domain walls from a configuration//to the chain axis at T < 40 K to a configuration of domain walls .L to the chain axis at T > 40 K could take place. These results indicate that the transition at 40 K is not a structural transition as ascertained by recent EPR measurements which show no change in g-values but reveal a redistribution of line ;ities below 40 K and various cooling rate and memory effects.(2) Implications for CD. transport at low temperatures will be discussed.
REFERENCES 1-
See in "Low Dimensional Electronic Properties of Molybdenum Bronzes and Molybdenum Oxides". C. Schlcnkcr ed., Kluwer Pub. (1989).
2-
J. Dumas ct al, Phys. Rcv. B 40, 2968 (1989) and Solid State Commun.72, 429 (1989).
Elsevier Sequoia/Printed in The Netherlands
3875
STUDY OF THE CHARGE DENSITY WAVE DEPINNING IN K0.3MoO 3 BY PROTON DECHANNELING
B. Daudin and M. Dubus C E N G - D R F - G / S B T - B P 85 X, 38041 Grenoble Codex, France. J. Dumas CNRS-Laboratoire d~Etudes des Propri~t6s Electroniques des Solides B.P. 166, 38042 Grenoble Cedex, France.
The blue bronze K0.3MoO3 shows a Peierls transition at 180 K towards an incommensurate semiconducting charge density wave (CDW) state. Non linear transport properties associated with the sliding motion of the CDW when the applied electric field exceeds a depinning threshold E t ha~been studied in details (1). Two different regimes of CDW conduction have been reported. Above 40 K, the onset of CDW sliding takes place at small threshold fields (Etl N 10 mV/cm) with a strong damping due to normal carriers. Below 40 K, large threshold values Et2 - 100 Etl are found together with an unusually low damping related to the nearly complete freezing out of the normal carriers. We have investigated the low temperature CDW state by proton dechanneling. The minimum backscattering yield Xmin increases dramatically below 40 K when the sample is cooled slowly from room temperature. No anomaly below 40 K is found after fast cooling, However, in the latter case, Xmin measured at 5 K is found to be strongly time dependent with time scales of the order of one hour. Negligible time dependence is found at - 50 K. In the explored temperature range 4 K < T < 50 K, when an electric field larger than threshold is applied after relaxation of Xmin, an increase of Xmin is observed. As an increase of Xmin always indicate an increase of the structural disorder, the large change in Xmin induced thermally or electrically reflects rearrangements of CDW structural defects. The abrupt change near 40 K in the time scales involved in these experiments may reflect a change m the domain structure. We suggest t h ~ a rotation of domain walls from a configuration//to the chain axis at T < 40 K to a configuration of domain walls .L to the chain axis at T > 40 K could take place. These results indicate that the transition at 40 K is not a structural transition as ascertained by recent EPR measurements which show no change in g-values but reveal a redistribution of line ;ities below 40 K and various cooling rate and memory effects.(2) Implications for CD. transport at low temperatures will be discussed.
REFERENCES 1-
See in "Low Dimensional Electronic Properties of Molybdenum Bronzes and Molybdenum Oxides". C. Schlcnkcr ed., Kluwer Pub. (1989).
2-
J. Dumas ct al, Phys. Rcv. B 40, 2968 (1989) and Solid State Commun.72, 429 (1989).
Elsevier Sequoia/Printed in The Netherlands