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Sliding of a charge density wave probed by coherent X-Ray Diffraction

Sliding of a charge density wave probed by coherent X-Ray Diffraction. E. Pinsolle Laboratoire de physique des solides, Orsay. Synchrotron Sources. Experiment done at the ESRF on the beamline ID10A. Experiment caried out by: E. Pinsolle V. Jacques D. Le bolloc’h A. Sinchenko

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Sliding of a charge density wave probed by coherent X-Ray Diffraction

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  1. Sliding of a charge density wave probed by coherent X-Ray Diffraction E. Pinsolle Laboratoire de physique des solides, Orsay

  2. Synchrotron Sources Experiment done at the ESRF on the beamline ID10A Experimentcaried out by: E. Pinsolle V. Jacques D. Le bolloc’h A. Sinchenko P. Monceau

  3. NbSe3 sample Threshold current 0.9 mA Sample dimensions: 2mm x 10μm x 10μm 3 types of chains: -first one with Peierls transition at 145K -second one with Peierls transition at 59K -last one with no transition.

  4. -2kF +2kF Signature of CDW in X-ray diffraction Gap opening at the fermi level. Satellite reflection (0 1.25 0) Electron density modulation Spawning of satellites around initial Bragg peak.

  5. Experimental setup Gold contacts Chain axis Diffracted Beam CCD camera Incident X ray beam Two interest of this experiment: -Coherent beam sensitive to phase defects. -Micrometer scale beam.

  6. Bellow the threshold 2D diffraction patterns I=0 mA Increasing current values Above the threshold I=0.2 mA I=1.4 mA I=0.4 mA I=1.6 mA I=0.6 mA I=1.8 mA I=0.8 mA

  7. First Result: Satellite in transverse direction. Satellite in the transverse direction for different current value, bellow (colon 1) and above (colon 2) the threshold. (IS=0.9 mA) Satellite with I=0.2 mA Satellite with I=1.8 mA

  8. Satellite in direction of chain axis for different current value, under (colon 1) and above (colon 2) the threshold. (IS=0.9 mA) Second Result: Satellite in longitudinal direction. -No speckle and no shape change. The shift δq= +/- 0.26 10-4 Å-1 which correspond in the real space to a change of the wave length δλ=+/-8.10-4 Å The shift of the satellite change sign when we exceed the threshold.

  9. Speckle signature of creep Bellow threshold Phase equation: -We suppose to be in a stationary case. - Correlations in longitudinal direction are much higher than in transverse direction. This lead to the following phase equation:

  10. Influence of steps above threshold Nb Se3 is known to have step at the surface Chain axis The CDW must vanish at the interface of the step.

  11. Speckle signature of creep Bellow threshold If some strong pinning defects are present on chain dn, this fixe the phase on these chain (φ(dn)=0) and leads to the solution: dn-1 dn dn-2 0 φn Φn-1 φ simulation from the previous theory compared to experiment.

  12. 2kF contraction Bellow the threshold. Theoretical explanation: where The total number of carriers is conserved. But when some current is applied we create a disequilibrium of the normal carrier densities. δq Approximate view of the band structure

  13. Current conversion above the threshold. Stress experienced by the CDW Chain axis Gold contacts Gold contacts δλ δq δλ=0 P. Monceau et al. Plastic sliding of charge density waves. Physical review B

  14. Conclusion Different behaviors of the CDW under current probed by coherent X ray diffraction: Bellow the threshold: Along the transverse direction. We observe phase defects which is the signature of creep phenomenon. Along longitudinal direction. Condensation of normal electrons in the CDW. Above the threshold: Along transverse direction. Influence of steps on the CDW. Along longitudinal direction. Current conversion far from contacts. Thankyou for your attention!

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