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We present the first results on the axion dark matter search in the axion mass range 10.13-11.17µeV at the Center for Axion and Precision Physics Research, Daejeon, Korea. The sensitivity is about 9 times larger than the Kim-Shifman-Vainstein-Zakharov coupling at 90% confidence level.

In the present paper, we ascertain two novel findings on chiral-index-selective binding/separating of single-walled carbon nanotubes (SWNTs) with a nonaromatic polymer, poly(dialkylsilane) (PSi). PSi is a typical σ-conjugated polymer, composed of alkyl side chains attached to the silicon (Si)-catenated main chain. First, PSi's with linear alkyl side chains showed significant diameter-selective wrapping for SWNTs with ca. 0.9 nm in diameter, resulting in the selective separation of (7,6) and (9,4) SWNTs. Its driving force was demonstrated to be cooperative CH-π interactions among the alkyl side chains of PSi's and the curved graphene of SWNTs. Second, the dynamic wrapping behavior of PSi's onto SWNTs was elucidated with time-resolved UV spectroscopy. Highly anisotropic UV absorption of PSi along the Si main chain was utilized as a "chromophoric indicator" to monitor the global/local conformations, which enabled us to track kinetic structural changes of PSi's on SWNTs. Consequently, we concluded that upon wrapping, flexible/helical PSi with an average dihedral angle (φ) of 145° and Kuhn's segment length (λ(-1)) of 2.6 nm interconverted to the more stiffer/planar conformation with 170° and λ(-1) of 7.4 nm. Furthermore, through kinetic analyses of the time-course UV spectra, we discovered the fact that PSi's involve three distinct structural changes during wrapping. That is, (i) the very fast adsorption of several segments within dead time of mixing (<30 ms), following (ii) the gradual adsorption of loosely wrapped segments with the half-maximum values (τ(1)) of 31.4 ms, and (iii) the slow rearrangement of the entire chains with τ(2) of 123.1 ms, coupling with elongation of the segment lengths. The present results may be useful for rational design of polymers toward chiral-index-selective binding/separating of desired (n,m) SWNTs.

The haloscope is one of the most sensitive approaches to the QCD axion physics within the region where the axion is considered to be a dark matter candidate. Current experimental sensitivities, which rely on the lowest fundamental TM 010 mode of a cylindrical cavity, are limited to relatively low mass regions. Exploiting higherorder resonant modes would be beneficial because it will enable us to extend the search range with no volume loss and higher quality factors. This approach has been discarded mainly because of the significant degradation of form factor, and difficulty with frequency tuning. Here we introduce a new tuning mechanism concept which both enhances the form factor and yields reasonable frequency tunability. A proof of concept demonstration proved that this design is feasible for high mass axion search experiments.

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