# Do electrons jump from one wire to another if they are of different materials?

I learnt from this answer to the question - Do electrons in a wire, actually jump across two metallic wires twisted together? - that electrons jump from one wire to another wire in contact, when electric current exists in both wires along the same direction, as shown below:

What happens if the two wires carrying current in the same direction are of different materials, say aluminium and copper, as given below?:

Will electrons jump from the copper wire to the aluminium wire and vice versa?

In the first case, the two wires are of the same material (say copper) and so at a given temperature, the drift speed of electrons as well as the lattice of the materials are same. So, it seems reasonable that electrons do jump from one wire to another.

But in the second case, since the wires are of different materials both drift speed and lattice of the materials are different in each wire. So, I think there must be some different in the way electrons drift between the two wires. Is this transfer kind of "one-way"? For example, will electrons flow only from the copper wire to the aluminium but not the other way round?

Let us assume that the two wires are in contact with each other (i.e., no oxide layer preventing electrical contact between them) and they are maintained at a constant potential difference. Is the combination of wires, simply a parallel or a more complicated one due to transfer of electrons between them?

Note: The above question was closed as a duplicate of tranfser of electrons between two metals and a wire. However, I didn't find it useful.

• Have u tried rubbing wool and plastic together? Jan 30, 2020 at 10:13
• @user6760: Yes. But I don't think triboelectric effect is involved here as there is no rubbing of materials. Could you elaborate how to visualise this using your example? Thanks. Jan 30, 2020 at 10:17
• Quantum mechanically, an electron has a probability to go between any two points as long as there is no finite region with infinite potential between them. Jan 30, 2020 at 11:15

Yes, they can jump between different materials. This is used all the time when engineering setups where the experimentalist wants to induce some new properties on the electrons in one of the materials. These are called heterostructures, and for example you can induce superconductivity in a semiconductor by proximity coupling them. The idea is that the electrons in the semiconductor can hop onto the superconductor and then return as holes, thereby inducing an effective (weak) superconductivity term in the semiconductor.

If you google "superconductor-semiconductor heterostructure" you will get ton of results.

• I'm not familiar with the "jumping" associated with semiconductors, but it seems to me the OP is asking about ordinary copper and aluminum conductors, not semiconductors. Jan 30, 2020 at 12:23

If electrons were not able to flow between two different conductors in contact with one another, we would not be able to make any connections in an electrical circuit that feeds loads. So obviously they can flow between conductors in contact with one another (twisted,or otherwise).

The term "jump" invokes the wrong impression that electrons need to leap through the air from one conductor to another, although as explained below arcing is possible at the conductor interface.

Although electrons don't have to "jump" between the conductors, it is more difficult for electrons to cross between two physically different conductors due to microscopic irregularities at the contact surfaces with points of contact and areas of non contact. Overall, this gives rise to what is referred to as contact resistance at the interface. Contact resistance, which is greater than the resistance of the conductor themselves, give rise to resistance heating, and sometimes overheating posing an ignition and fire hazard, particularly if electrical connections are not made properly. For this reason electrical connections are usually considered to be the weak links in an electrical circuit due to the possibility of overheating.

Incidentally, overheating was a problem for copper aluminum connections to to a combination of making poor connections and the partial incompatibility of the different materials.

Hope this helps.

• Thank you for your answer. Is the "contact resistance" same for both "copper to aluminium" flow and "aluminium to copper" flow of electrons? Jan 30, 2020 at 12:27
• I don’t have information on the difference in normal contact resistance copper-copper vs. copper-aluminum. However, as I understand it, the difference in coefficients of thermal expansion of copper vs. aluminum can, over time with thermal cycling, the connection to loosen, effectively increasing the contact resistance Jan 30, 2020 at 12:52
• No problem. However, I think you misinterpreted my follow-up question. I asked whether the resistance depends on the direction of flow of electrons - whether it's from copper to aluminium or aluminium to copper? I'm having this doubt due to the lack of symmetry on the basis of the lattice structure and drift speeds. Let's neglect differential thermal expansion. Jan 30, 2020 at 13:29
• Sorry. But I have never heard of the contact resistance for ordinary metal conductors (copper, aluminum, etc.) being dependent on the direction of current flow. You'll have to do your own research to find out. Jan 30, 2020 at 13:41