  The lack of transmissive photonic components in the extreme ultra-violet
(XUV) constitutes a challenge for micro/nano-metric confinement. Here, we
theoretically design a novel approach to attain XUV radiation guidance based on
the electromagnetic properties of Titanium-Aluminum-Titanium heterostructures
in such a spectral domain. We show that, thanks to the near-zero-index
properties of aluminum and titanium, XUV radiation can couple efficiently with
plasma oscillations in such heterostructures, enabling the excitation of
several distinct plasmon polariton modes. Our predictions, based on the
semi-analytical solution of fully vectorial Maxwell's equations, indicate that
the dispersion profile of plasmon polariton modes can get efficiently modulated
by the aluminum thickness, enabling nanometre confinement and micrometre
propagation length. Moreover, we quantify the third-order nonlinearity
enhancement factor, finding that it is resonant at the zero-index wavelength.
Our results are promising for the development of future devices enabling
advanced control and manipulation of XUV radiation.
