Question About Bloch Oscillation: Understand the Energy

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Discussion Overview

The discussion revolves around the concept of Bloch oscillations and the associated energy levels of electrons in a periodic potential. Participants explore the implications of the dispersion relation and the periodicity of energy in the context of Bloch's theorem, contrasting it with the extended zone scheme.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions the apparent contradiction in energy levels for different wave vectors (k=π/d and k=3π/d) in the extended zone scheme, noting that energy typically increases with k.
  • Another participant suggests that Bloch oscillations rely on a periodic dispersion relation and provides a form of this relation, indicating that it differs from the free electron model.
  • A participant proposes that Bloch's theorem implies energy periodicity over k, suggesting that varying n leads to the same energy for different k values, questioning the relevance of the extended zone scheme.
  • Another participant confirms the periodicity of energy according to Bloch's theorem and expresses uncertainty about the relationship between the extended zone scheme and the repeated-zone scheme.

Areas of Agreement / Disagreement

Participants generally agree on the periodic nature of energy levels as described by Bloch's theorem, but there is uncertainty regarding the implications of the extended zone scheme and its relationship to the discussion. Multiple competing views remain on the interpretation of these concepts.

Contextual Notes

There are limitations in the discussion regarding assumptions about the periodicity of the dispersion relation and the definitions of the extended and reduced zone schemes. Some mathematical steps and their implications remain unresolved.

Who May Find This Useful

This discussion may be useful for students and researchers interested in solid-state physics, particularly those studying electron behavior in periodic potentials and the implications of Bloch's theorem.

hafsa
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i have a question concerning BLOCH OSCILLTION.i studied that in the extended zone scheme, the energy of an electron with k=pi/d is same as with k=3 pi/d.
i can't understand this because by dispersion relation as wave vector increases ,energy also increases(in extended zone scheme too)
please help me
 
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well, if I'm not mistaken, bloch oscillations are based on the assumption that the dispersion relation is periodic [something like - e(k)=B+A*cos(a*k)]. when you derive the speed from this energy [by v=(1/h)*de(k)/dk] you get a sine - a periodic speed.
the reason that the dispersion relation is periodic and not e(k)=h^2*k^2/2m is that the later is true only for free electrons. when dealing with bloch electrons this formula isn't quite right. if you work with the tight binding method you get those periodic e(k) functions.
 
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hmm,u mean that in bloch oscillation we are actually apllying bloch theorem also.(by letting n vary,we obtain same energy for different energies of k(wave vector)and there is no role of extended zone scheme here.am i right?
 
sure. and according to bloch's theorem:
\epsilonn(k)=\epsilonn(k+G)
where G is any reciprocal lattice vector.
this means that at the same band (n) the energy is periodic over k.

regarding the extended zone scheme, I am not sure but as far as i understand it will be the same as the repeated-zone scheme (that is the reduced zone repeated).
 

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