I am having a real hard time understanding how I reach the expression that relates resistance and $\varepsilon''$ as the complex part of the dielectric constant.
I was trying to follow a clear and eloquent way of describing this. I understand how the idealized concept of a capacitor requires a $\pi/2$ phase shift between polarization and electric field which is related by the dielectric constant. If it is not $\pi/2$ , then expressing the the dielectric constant as a complex number will allow us to express that phase shift.
I know that not having a phase shift equal to $\pi/2$ means that I do not have a ideal capacitor, but also a related resistance.
My professors keep telling me that the following expression is a definition, not a deduction:
$$\varepsilon''=\sigma/{\varepsilon_0\omega} $$
i.e.
$$\varepsilon''=d/{A\varepsilon_0\omega R} $$ where d and A are thickness and contact area of the resistance R
But it seems to me that I should be able to explain it better... How?