IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Surface Science Wednesday Sessions
       Session SS3-WeA

Invited Paper SS3-WeA1
Medard W. Welch Award Lecture: Intertwined Charge Density Wave and Defect-Ordering Phase Transitions in a 2-D System@footnote 1@

Wednesday, October 31, 2001, 2:00 pm, Room 122

Session: Electronic Structure I
Presenter: E.W. Plummer, The University of Tennessee and Oak Ridge National Laboratory
Authors: E.W. Plummer, The University of Tennessee and Oak Ridge National Laboratory
A.V. Melechko, The University of Tennessee and Oak Ridge National Laboratory
Correspondent: Click to Email
The study of macroscopic properties of phase transitions in low-dimensional systems provides an understanding of the fundamental aspects of systems of interacting particles. Phase transitions are strongly affected by defects, especially in systems with lower dimensionality. In quasi-1D or -2D systems that exhibit a CDW transition, a small proportion of microscopic disorder can control the global properties because of the collective nature of the phenomena. It has been speculated that the interaction of mobile defects with CDW leads to alignment of defects with the CDW, or the formation of Defect Density Waves.@footnote 2@ In this dynamic picture, the distribution of defects is neither random nor static, instead defects align their positions to optimize the energy of the pinned CDW. Here, we will discuss a complex symmetry lowering (Ã3xÃ3) to (3x3) phase transition in Sn/Ge(111) and similar systems that can be decomposed into two intertwined phase transitions: a second order CDW transition and a first order disorder-order transition in the defect distribution. We present two phenomenological models that describe these transitions and their interrelation.@footnote 3@ These models allow us to understand the formation of the domains and domain walls seen in STM at low temperatures, defect-induced waves above the CDW transition temperature, and ordering of the defects caused by the CDW-mediated defect-defect interactions.@footnote 4@ The models predict a shift in the CDW transition temperature with impurity density and a dependence of the (3x3) lattice structure on the specific defect alignment. @FootnoteText@ @footnote 1@ Supported by NSF DMR 980130. ORNL is supported by the U.S. DOE through contract DE-AC)5-))OR22725 with UT-Battelle, LLCC.@footnote 2@ H. Mutka, in Advances in the crystallographic and microstructural analysis of charge density wave modulated crystals, edited by F. W. Boswell and J. C. Bennet, Kluwer Academic Publishers, Dordrecht, 1999.@footnote 3@ A. V. Melechko, M. Simkin, N. F. Samatova, J. Braun, and E. W. Plummer, submitted for publication.@footnote 4@ A. V. Melechko, J. Braun, H. H. Weitering, and E. W. Plummer, Phys. Rev. Letters, 83, 999 (1999). H. H. Weitering, A. Melesko, J. M. Carpinelli, and E. W. Plummer, Science, 285, 2107-2110 (1999).