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David Le Bolloc’h LPS Bât 510 Orsay Vincent Jacques N. Kirova Jean Dumas IN Grenoble

Observation of correlations up to the micrometer scale in sliding charge density waves. Bleu bronze K 0.3 MoO 3 by coherent X-ray diffraction. David Le Bolloc’h LPS Bât 510 Orsay Vincent Jacques N. Kirova Jean Dumas IN Grenoble S. Ravy Synchrotron Soleil. ECRYS 08.

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David Le Bolloc’h LPS Bât 510 Orsay Vincent Jacques N. Kirova Jean Dumas IN Grenoble

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  1. Observation of correlations up to the micrometer scale in sliding charge density waves. Bleu bronze K0.3MoO3 by coherent X-ray diffraction David Le Bolloc’h LPS Bât 510 Orsay Vincent Jacques N. Kirova Jean Dumas IN Grenoble S. Ravy Synchrotron Soleil ECRYS 08

  2. « Coherent diffraction » Transverse coherence length: xx xy Longitudinal coherence length: xl 2 2 Helmholtz: ( +k )U=0 x = l D / 2 a Taille du faisceau (Gaussien) Degree of coherence b: a z D

  3. « Coherent diffraction » Transverse coherence length: xl et xt 2 2 Helmholtz: ( +k )U=0 x = l D / 2 a Taille du faisceau (Gaussien) Degree of coherence b:  1 !! z 10µm D

  4. Source a ~ 1mm l= 5790 Å l= 5790 Å Visible light: x= l D / 2 a Rectangular aperture l= 1.5 Å X-rays: Source l= 1.5Å 2µm*2µm ~10 000 l! D. Le Bolloc’h et al. J. Synchrotron Radiat. 9, 258 (2002).

  5. Sr O • Phase transition (order-desorder in metallic alloys) superstructure (1/2 1/2 1/2) Pd3V AuAgZn2 F. Livet et al. PRB (2006) II) Displacive phase transition: « central peak » and the « second length scale» in SrTi03 central peak observed by X-ray (3/2 1/2 ½) superstructure at Tc+10K Narrow and broad component (AuAgZn2) Ravy, L.B.,Curat et al., PRL (2007)

  6. Bronze bleu K0.3MoO3 2kF CDW qc= a* 0.752b* -0.5 c* 10 Å qc b Beam size F Beam size F

  7. Bronze bleu K0.3MoO3 CDW Dislocation 2kF CDW r=ro + Dcos(qc r + f) qc= a* 0.752b* -0.5 c* Theory: Lee et Rice (1979) Golkov (1983) Ong and Maki (1985) Freidel Feinberg qc 10A Beam size F Beam size F Bulk CDW modulation D. Le Bolloc’h et al. prl (2005)

  8. Blue bronze under external current ? 2a*-c* (8 0 –4) QS (6 0.252 -3.5) Experimental setup: ccd (4 0 –4) (6 0 –3) 0.252 b* 26.4° 12.6° 2a*+c* E=7.6Kev at 75K 2mm V 10*10µm S2 DV/DI 10µm I (mA) Is=1.2 mA fs Cryostat ccd

  9. 2kF CDW Host lattice QS (6 0.252 -3.5) a) b) I=16*Is (6 0 -3) I=0 I=16*Is I=0 q q b* b* 2a*-c* ~ t* t* Each isosurface has been fixed at Imax/18 for the (6 0 -3) and Imax/7 for Qs. For clarity, the reflections with and without current have been shifted along b. The field-induced satellites are indicated by arrows. Each 3D acquisition lasted less than 15 mn.

  10. qs direction transverse : (6, 0.252 + qs, 3.5) with qs = 4.9 10−4 in b* units 1.2μm at I=0mA, 0.6μm at I=12 Is 0.4μm at I=16 Is L=1.5μm !!! 1500*lCDW (=4/3 b*=10.08A°) T.Tamegai et al., Solid State Commun. 51, 585 (1984); R.M. Fleming, R.G. Dunn, L.F. Schneemeyer, Phys. Rev. B 31, 4099 (1985).

  11. Threshold Is 2kF • 2kF is constant • Decreasing correlations for increasing current • Asymmetric profiles along b* • 4. δq appears in the sliding regime and saturates at ~3 mA • 5. δq corresponds to distances ranging from x=0.7 µm to 1.2 µm ! • 6. No speckle

  12. 1.7mA 4mA 2.3mA 2.7mA 1.3mA 15mA 7mA 10mA I=0mA I=1mA Transverse coherence length versus current

  13. r=h0 Cos[2kF+f(x)] DF=p/4 f(x) ~1µm d Experimental data Secondary fringes Dq 2kF

  14. Dislocation array ? r=h0 Cos[2kF+f(x)] φ(x) is a saw-toothed function. Inter-soliton distances and soliton width ajustable parameters. ~0.5µm f(x) ~1µm 2kF

  15. Amplitude modulation ? r=h0 Cos[2kF+f(x)] h h0 h I h0 h ~1µm h0 h h0

  16. Conclusions: Long range order up to the micrometer scale in sliding charge density waves. Temperature dependence? Relationship with sliding ? Is it universal in CDW systems ? D. Le Bolloc’h et al. PRL (2008) Vincent Jacques N. Kirova Jean Dumas IN Grenoble S. Ravy Synchrotron Soleil Poster « chromium »

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