Presentation on theme: "Sliding of a charge density wave probed by coherent X-Ray Diffraction E. Pinsolle Laboratoire de physique des solides, Orsay."— Presentation transcript:
Sliding of a charge density wave probed by coherent X-Ray Diffraction E. Pinsolle Laboratoire de physique des solides, Orsay
Synchrotron Sources Experiment caried out by: E. Pinsolle V. Jacques D. Le bolloc’h A. Sinchenko P. Monceau Experiment done at the ESRF on the beamline ID10A
NbSe3 sample 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. Threshold current 0.9 mA
Signature of CDW in X-ray diffraction Gap opening at the fermi level. Electron density modulation -2k F +2k F Spawning of satellites around initial Bragg peak. Satellite reflection ( )
Experimental setup Incident X ray beam Chain axis Diffracted Beam CCD camera Gold contacts Two interest of this experiment: -Coherent beam sensitive to phase defects. -Micrometer scale beam.
Above the threshold Bellow the threshold 2D diffraction patterns Increasing current values I=0 mA I=0.8 mA I=1.4 mA I=1.8 mA I=0.2 mA I=0.4 mA I=0.6 mA I=1.6 mA
First Result: Satellite in transverse direction. Satellite in the transverse direction for different current value, bellow (colon 1) and above (colon 2) the threshold. (I S =0.9 mA) Satellite with I=1.8 mA Satellite with I=0.2 mA
The shift of the satellite change sign when we exceed the threshold. -No speckle and no shape change. The shift δq= +/ Å -1 which correspond in the real space to a change of the wave length δλ=+/ Å Second Result: Satellite in longitudinal direction. Satellite in direction of chain axis for different current value, under (colon 1) and above (colon 2) the threshold. (I S =0.9 mA)
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:
Influence of steps above threshold Chain axis The CDW must vanish at the interface of the step. Nb Se3 is known to have step at the surface
If some strong pinning defects are present on chain d n, this fixe the phase on these chain (φ(d n )=0) and leads to the solution: simulation from the previous theory compared to experiment. dndn d n-2 d n-1 φnφn Φ n-1 0 φ Speckle signature of creep Bellow threshold
2k F 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. Approximate view of the band structure δqδq
Current conversion above the threshold. Stress experienced by the CDW Chain axis Gold contacts δλδλ δqδq δλ=0 P. Monceau et al. Plastic sliding of charge density waves. Physical review B
Conclusion Thank you for your attention! 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.