PHYS brown bag seminar: Looking for charge density waves
Topic presented by Hannu-Pekka Komsa (Electronic Properties of Materials). Join us for science and pizza in the Nanotalo lobby.
A partially filled one-dimensional metallic band should spontaneously develop periodic modulation of the electronic density and consequently of the related atomic coordinates. This fundamental phenomenon in solid-state physics is known as Peierls distortion or in more general context as charge density wave (CDW). It is most readily observed in metallic 1D systems as in step edges of semiconductor surfaces, but also in some quasi-1D or -2D bulk materials, e.g. NbSe2. Recent advances in nano-science have allowed construction of various artificial 1D or 2D structures and studying their structural and electronic properties in the atomic scale. Consequently it is now possible to directly observe the CDW formation and its evolution upon changing conditions. At the same time, the system can be accurately modeled using first-principles approaches, where both the electronic and structural degrees of freedom are accounted for on an equal footing, providing complementary information on the underlying physics.
Here, I first briefly introduce the charge density wave concept, both the original description by Peierls for 1D metallic system and some later refinements to the theory. I then present few examples from our recent work related to periodic modulations of atomic and/or electronic structure in 1D systems, consisting of grain boundaries in 2D materials and chains of atoms confined inside carbon nanotubes. Via combination of experimental results and computational modeling we aim to understand the extent to which the observed features can be understood within the classical Peierls picture and where something else must be going on.