  The polarization function of electrons with the tilted Dirac cone found in
organic conductors is studied using the tilted Weyl equation. The dynamical
property is explored based on the analytical treatment of the particle-hole
excitation. It is shown that the polarization function as the function of both
the frequency and the momentum exhibits cusps and nonmonotonic structures. The
polarization function depends not only on the magnitude but also the direction
of the external momentum. These properties are characteristic of the tilted
Dirac cone, and are contrast to the isotropic case of grapheme. Further, the
results are applied to calculate the optical conductivity, the plasma frequency
and the screening of Coulomb interaction, which are also strongly influenced by
the tilted cone.

Mesoscale and Nanoscale Physics