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Speed of light in a superconductor

  1. Jul 25, 2008 #1
    Could you please spot where is the fault in this reasoning? I suspect that some of the relations may not be applicable and needs to be substituted with something else (or I'm just making a gross mistake as usual...):

    Speed of light in a material:


    where permettivity is


    and suscettivity is

    [tex]\chi_m=\mu_r - 1[/tex]

    which describes the magnetization of the material due to an external magnetic field

    [tex]M=\chi_m H[/tex]


    A superconductor behaves like a perfectly diamagnetic material, suppressing the internal field B because

    [tex]\chi_m = - 1[/tex]



    [tex]\mu_r = 0[/tex]

    [tex]\mu = 0[/tex]


    which clearly makes no sense...
  2. jcsd
  3. Jul 25, 2008 #2
    there are also negative index of refraction materials
    which also mess that up.

    i think the subtlety is the phase vs group velocity
    of the light waves.


    "...The phase velocity of electromagnetic radiation may under certain circumstances (e.g. in the case of anomalous dispersion) exceed the speed of light in a vacuum, but this does not indicate any superluminal information or energy transfer..."
    Last edited: Jul 25, 2008
  4. Jul 25, 2008 #3

    Ben Niehoff

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    Also, in a perfect conductor, [itex]\epsilon = \infty[/itex]. I don't know if this applies to superconductors (but they do offer practically zero resistance, yes?).
  5. Jul 25, 2008 #4
    IIRC, the penetration depth of light into a conductor is proportionate to the resistivity, so in a perfect conductor light won't penetrate at all (the charge carries at the surface absorb all the light that isn't reflected).
  6. Jul 26, 2008 #5

    Vanadium 50

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    What you are discovering is that you don't have electromagnetic radiation inside an ideal superconductor.
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