Department of Physics, University of California, Berkeley
Materials Sciences Division, Lawrence Berkeley National Lab
Among the vast array of
phenomena associated with strongly correlated electron systems, charge density
wave (CDW) materials continue to garner much attention because of their
fascinating electrical properties including massive conductivity anisotropies.
Appearing in the ground states of many materials, the onset of the CDW state
results in an altered periodicity, the gapping of bands near the Fermi level,
and the formation of new electron or hole pockets, all of which Angle Resolved
Photo-Emission Spectroscopy (ARPES) is ideally suited to investigate. Tellurides
provide us with an exceptional opportunity to use ARPES to study CDW states
because of the expected size of the CDW generated band gap, its cleavability,
and the stability of its surface. Furthermore, the quasi-2D structure of these
materials means that much of the band structure can be understood in terms of
the 2D Te layers.
Our current research focuses on the Ditellurides CeTe2 and LaTe2 and exploring the band structures in the CDW state. ARPES can provide the critical data to resolve many points of controversy and ambiguity including the orientation of the CDW, the actual size and locations of the induced band gap, the Fermi surface band structure, the existence of 4-fold symmetry, and the proper characterization and understanding of the material's electrical properties. The figure below demonstrates the power of the ARPES technique in studying the band structure at constant energy and the beautiful structures that can be unveiled. In addition, with the discovery of pressure induced superconductivity in CeTex (x=1.82) coexisting with the CDW state, the study of these materials may lead to further insights and new questions about this remarkable electronic state.
Revealing Charge Density Wave formation in the LaTe2 system by
Angle Resolved Photoemission Spectroscopy
D. R. Garcia, G.-H. Gweon, S.Y. Zhou, J. Graf, C.M. Jozwiak, M.H. Jung, Y.S. Kwon, A. Lanzara
Phys. Rev. Lett. 98, 166403 (2007)