RKKY Interaction: Defining $\hat{H}$

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Discussion Overview

The discussion revolves around the Hamiltonian of interaction in the context of the RKKY (Ruderman-Kittel-Kasuya-Yosida) interaction, specifically focusing on the notation and indices used for fixed ions and conducting electrons. Participants explore the implications of the Hamiltonian's structure and the relationships between the indices.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant presents a Hamiltonian for the interaction between fixed ions and conducting electrons, questioning the use of subscript ##i## for both electrons and ions.
  • Another participant expresses concern about the index ##i## running from 1 to 2, suggesting it may be a bug and proposing that separate indices should be used for ions and conduction electrons.
  • A different participant clarifies that there are two fixed ions, with one ion polarizing an electron that interacts with a second ion, indicating an indirect interaction between the ions.
  • One participant agrees with the previous point but argues that the electron index should be independent of the ion index, noting that RKKY interactions occur in the conduction electrons of metals.
  • Another participant proposes that if an electron is near an ion, it could be approximated as being on the same lattice site as the ion, and raises a question about calculating a matrix element related to this problem.

Areas of Agreement / Disagreement

Participants express differing views on the appropriateness of the indices used in the Hamiltonian and the nature of the interactions described. No consensus is reached regarding the notation or the implications of the Hamiltonian structure.

Contextual Notes

There are unresolved questions regarding the definitions of indices and the assumptions about the lattice sites of ions and electrons. The discussion does not clarify the mathematical steps involved in the proposed calculations.

LagrangeEuler
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Hamiltonian of interaction between fixed ion and conducting electron
##\hat{H}=-J\sum_{i=1}^2\{\hat{s}_i^z\hat{S}_i^z+\frac{1}{2}(\hat{s}_i^+\hat{S}_i^{-}+\hat{s}_i^-\hat{S}_i^{+})\}##
Why both electron and ion are defined with subscript ##i##?
 
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...and why does i run from 1 to 2?

Looks like a bug to me.

One would think that you need separate indices i and j to label the atoms and the (conduction) electrons, and that these would run over the number of particles in question.
 
There is two fixed ions. One ion polarised electron and that electron interract with secound ion. So between ions is indirect interraction.
 
OK, that makes sense. However, I would still expect the electron index to be independent of the ion. Remember that RKKY occurs in the conduction electrons of metals.
 
Well I think that if electron is near ion you could approximate that it is on the same lattice site ion lattice site. I asked question about calculating matrix element in this problem.
Here is that question.
https://www.physicsforums.com/showthread.php?t=646675

I would be grateful if you could look and maybe answer this question.
 

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