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Events on Monday, October 8th, 2012

Plasma Physics (Physics/ECE/NE 922) Seminar
No seminar
Time: 12:00 pm - 1:00 pm
Place: 1310 Sterling Hall
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Condensed Matter Theory Group Seminar
Electronic properties of ultimate nanowires
Time: 4:30 pm
Place: 5310 Chamberlin
Speaker: Franz Himpsel
Abstract: Stepped semiconductor surfaces decorated with metal atoms make it possible to engineer the ultimate nanowire, a string of atoms connected by a single wave function. Such atomic wires form spontaneously for many metal-semiconductor combinations and thereby provide a playground for low-dimensional electron physics [1]. Angle-resolved photoelectron spectroscopy combined with scanning tunneling microscopy/spectroscopy reveals a variety of unexpected phenomena, such as atomically-precise ribbons of graphitic silicon and spin-polarized Fermi surfaces caused by the Rashba effect.

The broken bond orbitals are so localized at the step edges that they become fully spin-polarized, similar to isolated broken bonds (Pb centers). Density functional theory predicts a spin-polarized ground state which is closely coupled to the formation of a superlattice (neither can exist without the other) [2]. This resembles the situation in complex oxides (HiTc superconductors, multiferroics), where the spin, charge, and lattice degrees of freedom are strongly coupled and make it difficult to find a simple approximation of their electronic structure.

Two-photon photoemission spectroscopy [3] and scanning tunneling spectroscopy [4] provide support for spin-polarized silicon atoms by probing their characteristic minority spin state.


1. I. Barke et al., Low-dimensional electron gas at semiconductor surfaces, Solid State Commun. 142, 617 (2007);
Nuri Oncel, Atomic chains on surfaces, J. Phys. Condens. Matter 20, 393001 (2008);
J. Schaefer et al., Self-organized atomic nanowires of noble metals on Ge(001): atomic structure and electronic properties, New Journal of Physics 11, 125011 (2009);
P. C. Snijders and H. H. Weitering, Electronic instabilities in self-assembled atom wires, Rev. Mod. Phys. 82, 307 (2010).
2. S. C. Erwin and F. J. Himpsel, Intrinsic magnetism at silicon surfaces, Nature Communications 1:58 (2010).
3. K. Biedermann et al., Spin-split silicon states at step edges of Si(553)-Au, Phys. Rev. B 85, 245413 (2012).
4. P. C. Snijders et al., Spectroscopic evidence for spin-polarized silicon atoms on Si(553)-Au, submitted.

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