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I hope this is the right forum to ask this question. Is there a material (preferably thin, like a membrane) that changes its local conductivity (by that I mean the permeability for an electric field; I hope it's the right term) upon excitation with light or heat? I have no idea where to start my search for something like that.

Thanks a lot.

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Any semiconductor will do this. –  John Rennie Apr 4 '13 at 7:19
    
Who would have thought that the answer is that easy. Just to make sure that I understand you correctly, I can have a sheet of semi-conducting material, locally shine a laser onto it and it will change its conductivity properties? –  fabee Apr 4 '13 at 7:41
    
    
Thanks a lot. Since I cannot accept your answer, I can at least upvote your comment. –  fabee Apr 4 '13 at 9:16
    
You should probably accept Manish's answer since he at least put in the effort to write one :-) Accepting an answer flags the question as "answered" otherwise it sits in the "Unanswered questions" queue forever. –  John Rennie Apr 4 '13 at 11:27

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Semiconductors are the best examples of this, they have very significant temperature coefficients.

In general, any conductor has a temperature dependence regarding conductivity. Generally, heat decreases conductivity for metals. Semiconductors can go both ways; thermistors with both PTC (positive temperature coefficients) and NTC are readily available.


Regarding light: Metals generally aren't affected by light, but semiconductors are. When light strikes a semiconductor, electron-hole pairs are excited to the conduction band, increasing the conductivity. LDRs and photodiodes are examples of this. (Technically, all LEDs are photodiodes of a sort, just like all speakers can work as weak microphones)

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I have a small follow-up question. I am actually searching for some kind of foil or film for which I can change the permeability for an electric field locally with e.g. a laser. If I understood it correctly, such a thing is part of a laser printer. Do you know whether such foils exist and where one could buy it (I don't have the right terms to google it; I always end up at patents). Thanks. –  fabee Apr 5 '13 at 9:19
    
@fabee: Not sure. Liquid crystals seem like a good idea, but they're not linear dielectrics. However, photodiodes are affected by lasers. –  Manishearth Apr 5 '13 at 9:22
    
Alright, thanks –  fabee Apr 6 '13 at 6:33

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