Study of Charge Density Wave materials under current by X-Ray diffraction

QUICK INFORMATION
Type
Seminar
Start Date
10-01-2020 10:00
End Date
10-01-2020 11:00
Location
Room 337, Central Building
Speaker's name
Ewen BELLEC
Speaker's institute
University Paris-Saclay, France
Contact name
Claudine Roméro
Host name
Tobias Schulli
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When a current above a threshold value is applied to a charge density wave material (CDW), a new collective current is induced which is periodic in space and in time. To understand this collective CDW behavior, we studied the quasi-1D crystal NbSe3 and the quasi-2D TbTe3 using X-ray diffraction. Several large instruments facilities were used for this study, the beamline ID01 of the synchrotron ESRF in Grenoble and the free electron laser LCLS in Stanford.

First, thanks to the large transverse coherence length of the X-ray beam at LCLS, we were able to observe a loss of the CDW transverse coherence in NbSe3 when applying current above a threshold. We also observed a longitudinal compression of the CDW under current.

Then, at the ESRF, we used the micro-diffraction setup at ID01 where the X-ray beam is focused on a micrometer scale by a Fresnel Zone Plate. This small X-ray beam was used to scan the CDW locally by diffraction on NbSe3. In this sample, we observed a transverse deformation, which we didn’t expect, indicating a CDW surface pinning. Using a theoretical model of CDW electric charge transport by a periodic array of solitons and taking into account the CDW surface pinning measured at ID01, we show that this phenomena can explain several resistivity measurements from the literature.

Finally, we used the micro-diffraction setup to study the quasi-2D CDW material TbTe3 and measured the rotation of the CDW wavefronts under current. This rotation is continuous and changes sign when current goes from positive to negative values. What’s more, this CDW rotation presents a strong hysteresis loop at low current.

Finally, I will present some ideas for experiments using the high coherent flux available at ID01 to study CDW materials using Bragg holography, grazing incidence X-ray diffraction to study the origin of surface pinning in CDW, and finally using the high transverse coherence of the X-ray beam to study the periodic soliton lattice (having a period of the order of 1 micrometer) as a function of the distance to the electrical contacts.

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