Maxwell's equations and Quantum Physics

[Gavroy]

hi

i have to deal with a question, that i do not understand fully:
in my chemistry lesson, my teacher told me, that if you have an aromatic molecule and you put it into a time-constant magnetic field, this would cause electrons to move. if you are not that familiar with chemistry, all you probably need to know is, that aromatic molecules contain electrons that are like the particle in a ring, more or less free to move in a ring.

but as far as i know, if i have a conductor and i put it into a time-constant mangetic field. one does not see any currents at all.

here i have a link for you, that covers this question with some quantum mechanical calculations and they explain it with what they call" quantum coherence", but i do not understand what electromagnetic principle is behind this:

http://www.fefox.com/ARTICLES/AromaticRingCurrents.pdf"

probably, someone here can tell me, what electromagnetic effect actually causes this?
as i do not see, how i could get this from the maxwell equations?
sry, for my english, i am still practising it ;-)

 

[Simon Bridge]

The paper you reference describes it as a quantum coherence effect, but it is more usually described as a consequence of Ampere's law.

http://www.chem.siu.edu/chem343/c343lectures/c343grignard.pdf (15)

http://onlinelibrary.wiley.com/doi/10.1002/chem.200400457/abstract;jsessionid=E946863AEC9809F704B2DF65E63D67F9.d03t03

 

[Gavroy]

thank you, but why does this not happen in a conductor, that is placed in a magnetic field? or is it just too hard to measure?

so what my problem with this actually is, seems to be that i think that amperes law says, that if you have a current, then you also get a magnetic field, but not the other way around. so is this where i am wrong? does a static magnetic field also produce a current in a conducting material?

 

[Simon Bridge]

Technically it does. If you made a ring of superconductor, for eg. the current induced when a magnetic field is brought up persists for a very long time. It's just there are other things happening since there are are such a very large number of electrons in macroscopic conductors that the quantum effects wash out.

I gave you a bunch of references for the effect and the paper you provided had a reasonable explanation. It's just that it is "quantum". From my brief reading it looks like bringing the magnetic field up establishes the angular momentum state of the free electron cloud.

You cannot do an experiment with an unchanging magnetic field ... you have to bring it up sometime and take it away later. The changing field induces a current. It normally dies away very quickly so you can then do your constant field experiment.

I don't want to speculate too much - it seems to be an area of ongoing research. The fefox article suggests that a persistent current is not all that it going on - from that description, the applied vector potential sort-of "smooths the way" for the angular momentum state that has been set up so it keeps going.

There's no end of papers on this in scholar if you are really keen.