David Le Bolloc’h LPS Bât 510 OrsayVincent Jacques N. KirovaJean Dumas IN GrenobleS. Ravy Synchrotron Soleil

ECRYS 08

Observation of correlations up to the micrometer scalein sliding charge density waves.

Bleu bronze K0.3MoO3 by coherent X-ray diffraction

(Gaussien)

« Coherent diffraction » Transverse coherence length: x y

Longitudinal coherence length: l

Taille du faisceau

Helmholtz: ( +k )U=02 2

Degree of coherence :

z

D / 2 a

D

a

(Gaussien)

« Coherent diffraction » Transverse coherence length: l et t

Taille du faisceau

Helmholtz: ( +k )U=02 2

Degree of coherence :

z 1 !!

D / 2 a

D

10µm

ÅVisible light:

Source

Åa ~ 1mm

= D / 2 a

Source

Å

Å

2µm*2µm ~10 000

X-rays:

Rectangular aperture

D. Le Bolloc’h et al. J. Synchrotron Radiat. 9, 258 (2002).

Sr

O

II) Displacive phase transition: « central peak » and the « second length scale» in SrTi03

(3/2 1/2 ½) superstructure at Tc+10K central peakobserved by X-ray

Ravy, L.B.,Curat et al., PRL (2007)

superstructure (1/2 1/2 1/2)

(AuAgZn

2

)

F. Livet et al. PRB (2006)

I) Phase transition (order-desorder in metallic alloys)

Pd3VAuAgZn2

Narrow and broad component

Bronze bleu K0.3MoO3

2kF CDW

qc=a*0.752b*-0.5 c*

qc

Beam size

Beam size

10 Å

b

Theory:

Lee et Rice (1979)

Golkov (1983)

Ong and Maki (1985)

Freidel Feinberg

CDW Dislocation

Bulk CDW modulation

Bronze bleu K0.3MoO3

2kF CDW cos(qc r + )

D. Le Bolloc’h et al. prl (2005)

qc=a*0.752b*-0.5 c*

qc

Beam size

Beam size

10A

10µm

Cryostatccd

S2

fs

E=7.6Kev26.4°

ccd(6 0 –3)

2a*+c*

2a*-c*(8 0 –4)

(4 0 –4)

0.252 b*

12.6°

V10*10µm

QS (6 0.252 -3.5)

at 75K

Experimental setup:

Blue bronze under external current ?

2mm

DV

/DI

Is=1.2 mA

I (mA)

a) b)I=16*Is

I=16*IsI=0I=0

t

~ t*bb

2a*-c*

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.

QS (6 0.252 -3.5)

(6 0 -3)

2kF CDW Host lattice

1.2μm at I=0mA, 0.6μm at I=12 Is 0.4μm at I=16 Is

direction transverse :

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).

(6, 0.252 + qs, 3.5) with qs = 4.9 10−4 in b* units

L=1.5μm !!!1500*CDW (=4/3 b*=10.08A°)

qs

1. 2kF is constant2. Decreasing correlations for increasing current3. Asymmetric profiles along b*4. δq appears in the sliding regime and saturates at ~3 mA5. δq corresponds to distances ranging from =0.7 µm to 1.2 µm !6. No speckle

2kF

Threshold Is

1.3mA

1.7mA

2.3mA

2.7mA

4mA

7mA

10mA

15mA

I=0mA

I=1mA

Transverse coherence lengthversus current

0 Cos[2kF+(x)]

(x)

Experimental data

=/4

Secondary fringes q

~1µm

d

2kF

Cos[2kF+(x)]

φ(x) is a saw-toothed function.Inter-soliton distances and soliton width ajustable parameters.

2kF

(x)

Dislocation array ?

~1µm

~0.5µm

Amplitude modulation ?

I

Cos[2kF+(x)]

~1µ

m

Long range order up to the micrometer scalein sliding charge density waves.

Temperature dependence?Relationship with sliding ?Is it universal in CDW systems ?

D. Le Bolloc’h et al. PRL (2008)

Conclusions:

Vincent Jacques N. KirovaJean Dumas IN GrenobleS. Ravy Synchrotron Soleil

Poster « chromium »