Direct phase determination of fractional reflection in charge-density-wave crystals using x-ray multiple diffraction

Shih-Lin Chang,^a Chao-Hong Du,^b,c Mau-Tsu Tang,^c Yu. P. Stetsko,^c Yen-Ru Lee,^a Tsong-Tze Lin,^a Shih-Chang Wong^a and Wen-Shien Sun^a

^aDepartment of Physics, National Tsing Hua University; ^bDepartment of Physics, Tamkang University; ^cNational Synchrotron Radiation Research Centre, Hsinchu, Taiwan, 300, R.O.C. (slchang@phys.nthu.edu.tw)

We report the direct determination of collective phase of charge-density wave (CDW) [1, 2] in a quasi-two-dimensional material 2H-NbSe₂ using the multiple diffraction technique. Via the coherent interaction between the X-ray waves propagating in the CDW modulated structure and the host structure, the collective phases of CDW were determined to be either 0^o or 180^o from the analyses of the asymmetry of the diffraction profiles along the azimuth scans of a CDW fractional reflection. The phases were observed not to vary with changing temperature, suggesting that the phases are pinned. This finding may be useful for the direct observation of the dynamic phenomena caused by the phase of the density waves.

References

1 Thorne, R. E. (1996) Physics Today, May 42-43.

2 Overhauser, A. W. (1978) Advances in Physics 27, 343-357.