Ab initio approach to magnon-electron coupling

\newcommand{\el}{\textit{et~al}.} The electronic properties of magnets and exchange-enhanced paramagnets are strongly influenced by the spin-flip fluctuations. In particular, their important role in the pnictide high-temperature superconductivity is has been conjectured [Mazin \& Johannes, \textit{Nat. Phys.} \textbf{5}, 141 (2009)]. To formulate a parameter free model of electron-electron interaction involving emission and absorption of magnons we combine our recently developed implementation of the linear response time dependent density functional theory for spin fluctuations [Buczek \el, \textit{Phys. Rev. Lett.} \textbf{105}, 097205 (2010)] with the methods of many body perturbation theory [Vignale \& Singwi, \textit{Phys. Rev. B} \textbf{32}, 2156 (1985); Zhukov \el, \textit{Phys. Rev. Lett.} \textbf{93}, 096401 (2004)]. This theoretical toolbox is applied to the description of recent inelastic tunneling spectroscopy experiments [Balashov \el, \textit{Phys. Rev. Lett.} \textbf{97}, 187201 (2006)], which have shown that the emission of magnons by electrons can open additional tunneling channels and increase conductivity. As second application, we discuss a scheme of the magnon mediated Cooper pair formation in PdH$_{x}$ and LaFeAsO.