It’s not. Superconductors are the most efficient electric conductors.
But silver (yeh I realize, I was an $$$$$$$$$$$$$$$$$dollar) is the most effective conductor of metallic. Why? It’s not simple. I’m sorry. I would like it to be easy but it’s not. Resistivity is the result of interactions with electrons, as well as the causes of scattering (that includes all non periodicities within the crystal’s lattice) like phonons, other electrons grains, grain boundaries and dislocations. The equations used to calculate the resistanceivities are not linear, and require an integral calculation of conductivity tensor that looks like this:
si,j=e24p3tk vi(k )vj(k )dS |v (k )|si,j=e24p3tk-vi(k-)vj(k-)dS-|v-(k-)|
where (k )v-(k+) refers to the collective velocity tt the relaxation period, and k.k.-, the vector in inverse space which ends on the Fermi surface (that is the Sthat you are integrating HTML26 onto). Shape of the Fermi surface is among the main factors that affect the conductivity.
Calculating it, particularly for metals that transition, isn’t simple to put it mildly.
If you’re looking to know more about the significance of this equation (and it’s only scratching the surface), ….) take a look at all ofthe following: