Abstract
We predict an optical effect associated with systems which exhibit topologically protected states separated by a finite distance. We develop a tight-binding model to calculate the optical selection rules in linear chains of atoms of different lengths, and show the crucial importance of edge states. For long enough molecules the interband transitions involving these edge states are in the highly sought-after THz frequency range. Although we have specifically considered finite carbon chains terminated by gold nanoparticles, the main results of our work can be generalized to various systems which exhibit topologically protected states separated by a finite distance.
Highlights
Carbyne has attracted much interest and its fair share of controversy since the first claims of its discovery in the 1960s [1,2,3,4,5,6], a detailed history of which can be found in Ref. [7]
We predict an optical effect associated with systems, which exhibit topologically protected states separated by a finite distance
We have considered finite carbon chains terminated by gold nanoparticles, the main results of our paper can be generalized to various systems, which exhibit topologically protected states separated by a finite distance
Summary
Carbyne has attracted much interest and its fair share of controversy since the first claims of its discovery in the 1960s [1,2,3,4,5,6], a detailed history of which can be found in Ref. [7]. We consider finite polyyne chains, i.e., a series of consecutive alkynes (−C ≡ C−)n with n greater than 1, with the end carbon atoms not necessarily being terminated by hydrogen atoms, but, for example, attached to gold nanoparticles [see Fig. 1(a)]. For these chains we study optical transitions, which arise due to finite-size effects. The presence of the gap in the energy spectrum of an infinite carbyne chain is well known [7], what is less well known is the emergence of two edge states within the gap when the chain is of finite size. It should be noted that structural distortions like solitons and polarons lead to extra levels appearing in the optical gap [22], these are often associated with chains charged via doping with strong electron withdrawing species, which is beyond the scope of this paper, and a topic for future study
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