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My question refers to the photoelectric effect. I have heard that it is possible, that for one photon, two electrons leave the irradiated metal. Is this correct and by which process can this be explained?

My thought was, that this could be possible, if two electrons are in the same state, but this is forbidden by Pauli's principle.

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  • $\begingroup$ Have you tried searching Google for "two photon photoemission"? It's possible if the sum of the energies of the two photons is greater than the work function. $\endgroup$ – garyp Nov 14 '15 at 14:57
  • $\begingroup$ This was not my question. My question was, whether one photon can emit two electrons. $\endgroup$ – Joe_base Nov 14 '15 at 15:25
  • $\begingroup$ a more modern view of the photon absorption : Some Non-Perturbative and Non-Linear Effects in Laser-Atom Interaction $\endgroup$ – user46925 Nov 26 '15 at 6:58
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It is possible and it has already been observed. In the following article they suggest both single and double step emission mechanisms:

Two Electron Photoemission in SolidsR. Herrmann, S. Samarin, H. Schwabe, and J. Kirschner Phys. Rev. Lett. 81, 2148 – Published 7 September 1998

The single step emission process is because of correlletions of the two electrons that will be emitted. Or as they say:

If we imagine the process of photoionization as interaction between one photon and one electron, it is obvious that the simultaneous emission of a second electron requires a direct interaction between both electrons.

In the double step processes the photon is absorbed by one electron which transfers part of its energy to the second electron. Two examples from the article are:

As an example for a double step process, we consider the excitation of a photoelectron from a core level and the subsequent filling of the core vacancy by a valence electron, leading to the emission of a second valence electron via an Auger mechanism. These processes are well known, and have been widely studied in various solids [8]. As a further double step scenario for a two-electron photoemission, we suggest the combination of a single photoionization in the valence band and a subsequent collision between the photoelectron and a second band electron leading to the emission of both electrons.

Note that the first mechanism is already used in surface analysis methods like AES.

As a last note I would like to point out that when working with metals (and solids in general) you should always work within the framework of "Band theory for solids"!

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    $\begingroup$ I'm inclined to argue that there is a bit of semantics that can confuse here. This is one photon in, giving two elections out, but the electrons are really "doing the work". Is there a scenario in which two electrons are emitted by some kind of Compton scattering effect? $\endgroup$ – Mikael Fremling Jan 7 '16 at 11:08
  • $\begingroup$ I have to admit I can't really come up with a good answer to that question. $\endgroup$ – David VdH Jan 7 '16 at 12:31
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No because according to particle nature of light there is a collision between an electron and photon. Thus one photon can emit only one electron the rest energy get converted to overcome collisions by other metal atoms and kinetic energy.

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