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Measuring effects of magnetic field on electrons in a tunneling state

  1. Apr 20, 2007 #1
    I am interested in measuring the effects of a magnetic field on an electron in a tunneling state. I know very little about solid state and I have very little experimental experience.

    In order to learn what is required to perform such an experiment, I thought I would pose my question here:

    How can one demonstrate experimentally that tunneling electrons are affected by a magnetic field?
  2. jcsd
  3. Apr 20, 2007 #2


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    Your question is not easily answered AS IS, and I will tell you why.

    What you intended to do here is something like this. Have two metals sandwiching an insulating barrier that is the tunnel barrier. You then want to apply a magnetic field JUST TO THE BARRIER to see how the tunneling process is affected by it.

    This isn't trivial to do. In fact, it is extremely difficult because

    (i) the coherence length is often very short (order of 10's of nanometers) for a charge carrier in metals. So you have to make the insulating barrier rather thin;

    (ii) because of (i), it is almost IMPOSSIBLE to "focus" a magnetic field JUST ON THE BARRIER. Inevitably, you will have the whole contraption, and certainly a large part of the metal itself, under a magnetic field. You now can't tell if any changes in measurement is due to just the tunneling process being affected by the magnetic field, or is the magnetic field also affecting the non-tunneling charges in the metals, even if it can only penetrates up to the skin depth into the metals.

    So what do we normally do to investigate how magnetic field can in fact influence of magnetic field in the tunneling process? We make insulating barrier that have magnetic moments. Oxides such as Cr2O3, etc. have magnetic moments that can interact with the tunneling particles. Such experiments have shown a very different tunneling spectroscopy, especially in the current versus voltage curve (IV curves), where the "background" shows a linearly increasing curve instead of the "flat" ones that are typically observed. This observation has been attributed to the inelastic scattering of the tunneling particles with the magnetic barrier[1]. In a non-magnetic barrier, most of the particles tunnel through ballistically.


    [1] J.R. Kirtley and D.J. Scalapino, Phys. Rev. Lett. v.65, p.798 (1990).
    Last edited: Apr 20, 2007
  4. Apr 20, 2007 #3
    Perfect! That is just the sort of answer I was hoping for. Of course it will take me a long time to absorb the prerequisites, but at least now I have a direction to head.

    I will grab a copy of your Phys Rev reference asap.
  5. Apr 20, 2007 #4
    I really like this idea. But the paper you cited dealt with superconductivity. Can't we just set up a tunneling current through a magnetized insulator? What substances would work?
  6. Apr 27, 2007 #5
    Progress report

    Hi Friends,

    I've been reading as much as I can about solid state experiments. I am still learning, so I am not sure what makes sense and what doesn't.

    Hence my participation in this forum.

    Would it be possible to perform a Stern-Gerlach-like experiment using electrons that were exposed to a magnetic field while they were in the tunneling state?

    I have a setup in mind if anyone would like to shoot holes through it.
  7. Apr 27, 2007 #6


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    I don't get it. Is there a reason why you want to do this? Have you looked at spin-polarized tunneling?

  8. Apr 27, 2007 #7
    Well, you know that I am interested in how tunneling electrons behave in a magnetic field. At first I thought the Lorentz force would be a good effect to look at, but then I learned a little more and I thought maybe the effect of the magnetic field on spin would be better to study.

    No, I do not know what spin-polarized tunneling is, but I will look it up shortly.
    Thank you for the suggestion!
  9. Apr 27, 2007 #8
    I hope this is what you meant - I was led to tunneling magnetoresistance. But the little description I read said only that spin was assumed conserved during tunneling.

    What if the receiving ferromagnet was not present, and the electrons just went into some detector. Would the spin up electrons and the spin down electrons deflect in different directions like the did in the stern-gerlach experiment?
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