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I Why is the valence band maxima at k = 0?

  1. Jul 24, 2016 #1
    In general, materials are either direct or indirect materials. For direct materials, both the valence band maxima and the conduction band minima are at k = 0. For indirect materials, only the valence band maxima is at k = 0 and the conduction band minima is at some other non-zero value of k. In all the books I've read, it seems to always be assumed that the valence band maxima is at k = 0. Is this true, and if so why?
  2. jcsd
  3. Jul 25, 2016 #2

    Dr Transport

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    by definition
  4. Jul 25, 2016 #3
    I have always seen the same, I think it's arbitrary defined like this.
  5. Jul 25, 2016 #4
    After some digging, I found that it actually isnt true that the valence band maxima is always at k = 0. In lead sulfide for example, the valence band maximum is at the L point.
  6. Jul 26, 2016 #5


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    Graphene and gaphite also come to my mind.
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