# Ideas for a paper

1. Apr 8, 2004

### Jupiter

I have to write an 8-10 page paper for my modern physics class. I was hoping someone here with more experience could suggest an interesting and accessible topic. The paper is going to have to be pretty long, so I'm going to have to be able to study this topic without getting severely lost in the physics and/or math.
We just began discussing Schrodinger wave equation, to give you an idea of where I am.
I not sure what to pick, and I'm afraid that no matter what I choose, it will either be too easy, or too difficult.
My professor suggested that I report on recent physics research papers involving principles (eg, Compton effect, photoelectric effect, electron diffraction) that we have studied this semester, but this sounds quite intimidating. Do you know of any research that would be easily understood by someone just starting out in QM? If not, how can I go about finding some?
My options are not limited to this, so any other suggestion is welcome. Please try to provide some good resources if you can about the topic you suggest.

2. Apr 8, 2004

### ZapperZ

Staff Emeritus
OK, I may have a "juicy" one here for you. :)

I am guessing that you have studied (or even done this experimentally) the photoelectric effect. Now, you know that the standard photoelectric effect model states that if the photon energy is below the material's work function, no matter how intense the light source is, you will not get any electron emission from the surface, ya? This is how we determine (at least in an undergraduate lab) the work function of a material, by plotting the photocurrent versus the photon energy and looking at x-intercept.

Anyway, what if you write about on a similar phenomena that VIOLATES this model? :) In particular, write about the fact that you CAN get photoelectrons using photons with energy LESS than the work function - via the multiphoton absorption process. Unlike the standard photoelectric effect, multiphoton absorption involves the absorption of not one, but two or more photons by the valence electron, the total of which can exceed the work function and thus, it can escape the material.

This multiphoton phenomena is of course, a higher-order process and so such technique has a lower probability of occuring than the single-photon process. This means that you do not get as many photoelectrons. The technique is so well-known that it is used to study the surface/image states of various materials.

A website that describes one of this effect, the 2-photon process, can be found here:

http://www.physik.uni-marburg.de/of/2ppe.html [Broken]

If you do choose this topic, you're welcome to contact me if you need further assistance. I will be away for the Easter weekend, but will be back online by Monday. I think this would be a neat topic to cover since it has some relevance to what you may have learned, but is just another example on why certain things in physics are valid only within certain ranges.

Zz.

Last edited by a moderator: May 1, 2017
3. Apr 8, 2004

### Jupiter

Hi Zapper. That idea is right along the lines I need. It sounds like a perfect fit to what the professor wants. I will suggest it to my professor (I need his approval). Thanks for offering to help me with the project. The paper is due May 7, so it's not crucial if you're gone one weekend. I'll pm you (other method prefered?) if I need help.
Stephen

4. Apr 8, 2004

### ZapperZ

Staff Emeritus
You may contact me however you wish, either via open discussion on here, via pm, or via direct e-mail.

Cheers.

Zz.

5. Apr 11, 2004

### Jupiter

Zapper, do you know who wrote the pioneering papers on this topic? When was this phenomenon discovered, etc?

6. Apr 11, 2004

### ZapperZ

Staff Emeritus
Which topic in particular are you refering to, the photoelectric effect, or the 2-photon/multiphoton effect?

The photoelectric effect is rather famous, as I am sure you know. Pioneering work in that was done of course by Einstein in coming up with the PE model using "photons". Almost all of the experimental verifications of Einstein's PE model were done by Millikan. When this phenomenon was first discovered, I don't quite know. Maybe someone else here has this information.

Zz.

7. Apr 11, 2004

### Jupiter

I meant the multiphoton effect. I'm having difficulty with finding articles on the multiphoton effect that explain it at a sufficiently elementary level that I can understand.

8. Apr 12, 2004

### ZapperZ

Staff Emeritus
I think the link I gave earlier should give a "simple" explanation of the 2-photon effect.

The problem here is that to be able to understand the multiphoton phenomena, you have to first understand the single-photon photoemission. While the classic photoelectric effect is "simple", the full-blown theory of it isn't since it explicitly involves the material itself. So almost all the discussions on the multiphoton photoemission assumes that the reader already understands the single-photon process already.

If you choose to do this, you first must discuss the single-photon photoemission process, not in the complicated terms, but at least beyond the simple PE effect model. I would suggest you tackle this process as done on metals. This means that you have to learn a little bit about metal's energy band structure (remember that I said that the photoemission process involves the material being looked at). Then you have to learn about the Spicer's Three-Step Model (google this). Only then can you start to include the 2-photon process. I suggest you limit yourself to 2-photon effects, but also include a discussion that higher-order process are also possible. I can give you technical papers where these processes have been used to study image states of various surfaces. So you can include a discussion on the applications of the multiphoton photoemission.

BTW, a number of you have asked me if my "avatar" on the left is a "comet". No, it isn't. It is an actual experimental "image" of a band structure of a high-Tc superconductor taken using angle-resolved photoemission spectroscopy(ARPES). We published this in PRL about a couple of years ago. If you have heard about the brouhaha surrounding the "kink" in the high-Tc spectrum, well this set of data is one of those in the middle of the whole controversy. So maybe, if you think the multiphoton photoemission might be too daunting, maybe you want to consider writing on ARPES instead! They are both in the same ballpark! :)

Zz.

Last edited: Apr 12, 2004