Free
charge carriers confined to atomic chains such as the gold-induced
superstructures on the stepped Si(553) surface enable experimental
insight into one-dimensional physics. Embedding into the higher dimensional
substrate allows for additional couplings between the free charge
carriers and their surroundings, which might modify the one-dimensional
characteristics. The gold atom superstructures on Si(553) consist
of a parallel arrangement of metallic chains from Au and Si atoms
on the terraces and of parallel Si step edges with some of the Si
atoms having dangling bonds with one unpaired electron. The metallic
chains give rise to localized plasmonic excitations. We have studied
these plasmonic resonances with infrared spectroscopy that enables
the detection of resonance shifts as small as 1 meV or even less.
The plasmonic behavior of the conductive chains of the high- and the
low-coverage gold superstructures on Si(553) is investigated at various
temperatures and additionally after filling electrons into certain
electronic states by placing gold adatoms onto the high-coverage structure.
When cooling to 20 K, the strong plasmonic signals of the undoped
superstructures become even stronger but shift to lower frequencies,
which is attributed to the temperature dependent change of the orientational
polarization of the Si dangling bonds. Regarding their plasmonic resonance
shifts, the conductive atom chains work just like refractive index
sensors.
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