Charge Order Fluctuations in One-Dimensional Silicides

Changgan Zeng1, P. R.C. Kent2, Tae-Hwan Kim2, An-Ping Li2, and Hanno H. Weitering1,3

1Department of Physics and Astronomy, The University of Tennessee, Knoxville
2Center for Nanophase Materials Sciences, Oak Ridge National Laboratory
3Materials Science and Technology Division, Oak Ridge National Laboratory

Achievement

Exceptionally long and uniform YSi2 nanowires have been fabricated via self-assembly of yttrium atoms on Si(001). The wire widths are quantized in odd multiples of the Si substrate lattice constant. An electronic phase transition from a metal to a charge-ordered insulator has been revealed on the nanowires. The thinnest wires, 3asi-wide, represent one of the closest realizations of the isolated Peierls chain, exhibiting van Hove type singularities in the one-dimensional density of states and charge order fluctuations below 150 K. The structure of the wire was determined through a detailed comparison of scanning tunneling microscopy data and first-principles calculations. Quantized width variations along the thinnest wires produce built-in Schottky junctions whose electronic properties are governed by the finite-size and temperature-scaling of the charge ordering correlation.

Significance

Our observations provide clear evidence for short-range charge order in one-dimensional chains that are electronically decoupled from neighboring chains and from the semiconducting substrate. They capture a rare glimpse in real space into the destruction of one-dimensional charge order at higher temperature. Both charge ordered insulating phase and metallic phase have been manifested on individual nanowires as a metallic I-V spectrum on the 5asi-wide side and an insulating one on the 3asi-wide side. This one-dimensional Schottky-type barrier device can be controlled by varying the temperature around the charge ordering transition. These remarkable nanowires with built-in junctions illustrate how the finite-size- and temperature-scaling behavior of a collective phenomenon might one-day be exploited in novel nano-architectures.

Publication

“Charge Order Fluctuations in One-Dimensional Silicides,” Changgan Zeng, P. R.C. Kent, Tae-Hwan Kim, An-Ping Li, and Hanno H. Weitering, Nature Materials 7, 539 (2008).

The research was sponsored by the National Human Genome Research Institute, National Institutes of Health Grant R01HG002647 (CZ), NSF (CZ) and by U. S. Department of Energy through the Center for Nanophase Materials Sciences, which is sponsored by the Division of Scientific User Facilities, and through computational resources from the National Energy Research Scientific Computing Center and from the National Center for Computational Sciences at Oak Ridge National Laboratory, which are supported by the Office of Science.

STM topography of YSi2 nanowires. a, Large scale STM image of self-assembled YSi2 nanowires on Si(001). The scale bar corresponds to 50 nm. b, High resolution filled-state STM image scanned at RT. c, Simulated filled-state STM image on a 3aSi-wide YSi2 nanowire adopting the structure model as shown in Fig. b. d, Cross-sectional line profile on a 3aSi-wide YSi2 nanowire.

Charge ordering in YSi2 nanowires.
a, STM image scanned at 40 K. The scale bar represents 5 nm. b and c, Registry aligned dual bias STM images scanned simultaneously at 40 K with a sample bias of -0.8 V and 0.8 V, respectively. d, Line profiles along lines ‘a’ and ‘b’ in b and c, respectively. The curves are shifted vertically for clarity. e, Statistical distributions of the spacings between neighboring charge density maxima in filled-state STM images for different temperatures. f and g, STM images of 5aSi-wide and 7aSi-wide YSi2 nanowires at 40 K. The image widths in f and g are both 14 nm. There is no charge ordering.