conductor=copper
insulator=polyethylene
semiconductor=graphite
perfect=mercury-barium-calcium-copper oxide at <= – 140C

 

A bit of theory might help explain. Engineering,, electronics, materials science, physics and chemistry all come together on this topic.

Conductivity is caused by the cooperative behavior of electrons that creates a unique quantum state that can be described as a kind of fluid or gas.  Conduction electrons are donated to the “conduction band” by atoms or molecules that can carry a positive charge as a result. (Electrons are  negative).

Take a look at the picture below to get an easier insight

 

Some metals are better than others, it helps to keep the positive lattice thermally steady, so that means a heavy nucleus. But such elements are rarer and thus expensive. Gold conducts better than copper which is better than aluminum. They do in fact use aluminum wires for long distance high tension transport on those big pylons. It is a cost-benefit calculation. And copper can be given gold plating to improve contacts because oxidation of metals produces non conducting oxide layers. Often just reseating a component can fix electrical circuit faults in older equipment by abrading oxide buildup.
In conductors, the energy to create the conduction band is called the “band gap”.

Semiconductors have a larger band gap so not as many electrons can make the jump.  And they may have another trick. An electron jumping back to the atoms creates a positive “hole” that can travel in the opposite direction, a bit like a gap in the traffic can move opposite to the traffic flow.

Take a look at the picture below to get an easier insight

For insulators, the band gap is too high to hold any electrons. This is often the case when the outer electrons of atoms are already involved in strong directional bonds to other atoms, such as in polymeric materials with large 2D or 3D structures like plastics and ceramics. Although in the future we may begin to see conducting polymers with electron paths or “highways” built into the molecules. Even conducting biomolecules should become possible.

Take a look at the picture below to get an easier insight

Superconduction needs the low temperature to keep the positive metal lattice still, and to create conditions to allow a special long-range pairing of electrons into “Cooper pairs”.

Electron behavior can be decomposed into two components or two fluids which coexist. In a superconductor, a time-dependent current will be carried both by the Copper pairs (superfluid component) and by the unpaired electrons (normal component).

But if you imagine for example transmitting gigabit Ethernet over superconducting wires, you may not be aware that at high frequencies oscillations induced in the normal electrons by a time-varying EM field will dissipate power.

 

 

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