Why does doping make resonating valence bonds (singlet pairs) mobile?

In summary: Pros and cons of Resonant Valence Bond Theory:-Pros: it is a simple and straightforward theory which does not require a lot of special assumptions or calculations.-Cons: it is not well supported by experimental evidence at the moment.
  • #1
Faizan Samad
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TL;DR Summary
I'm a first year masters student so I'm looking for a qualitative, possibly intuitive explanation, rather than a math heavy quantitative one. This is for a presentation for my class.
I know in RVB theory that neighbouring Copper atoms form singlet pairs via the superexchange "force". Upon doping with holes, these neutral singlet RVB pairs become mobile and charged and are able to superconduct. I know that the resonating valence bonds are in the copper 3d(x^2-y^2) orbital and when hole doped, these are the electrons that are removed. My questions are, why are they called neutral singlets when they are undoped? And why does doping allow them to become mobile? I read that they separate into fractional quasiparticles as holon-antiholon pairs when they are hole doped. Are these mobile RVBs "traveling" through holes or am I completely missing the picture? Also I have read a lot of papers from PW Anderson and G Baskaran and I am still a little confused as to what makes RVBs mobile superconductors upon doping. Thank you. Any help is appreciated
 
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I am afraid that I can't help answer the specific questions; but it is perhaps worth pointing out that RVB is -most likely- not an actual explanation for HTS. which could be one reason for your confusion It was a very early theory, and does not -as far as I am aware- agree with experiments (at least in its "plain" form)
Hopefully, you are already aware of this and is studying this for "historical" reasons.
 
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  • #3
Faizan Samad said:
My questions are, why are they called neutral singlets when they are undoped?
The charge of electron pair (of Mott insulator in this case) is canceled by polarization of surrounding material when the pair is immobile. When pair is mobile, the lagging polarization can no longer fully cancel its charge.

I must also agree with @f95toli - the experimental proof for RVB (resonant valence bond) theory is substandard at the moment. The theory may be simply untrue.
 

1. Why is doping used in materials to make resonating valence bonds mobile?

Doping is used in materials to make resonating valence bonds mobile because it introduces impurities into the crystal structure, disrupting the regular arrangement of atoms and creating defects. These defects act as energy states, allowing the resonating valence bonds to move more freely and increase their mobility.

2. How does doping affect the mobility of resonating valence bonds?

Doping increases the mobility of resonating valence bonds by creating defects in the crystal structure that act as energy states. This allows the bonds to move more easily through the material, making it more conductive.

3. Can doping make all types of resonating valence bonds mobile?

No, doping can only make certain types of resonating valence bonds mobile. It depends on the specific material and the type of doping used. Some materials may not have resonating valence bonds that can be made mobile through doping.

4. Are there any drawbacks to using doping to make resonating valence bonds mobile?

Yes, there can be drawbacks to using doping to make resonating valence bonds mobile. Doping can introduce impurities into the material, which can affect its overall properties and stability. It can also be difficult to control the amount and distribution of doping, leading to inconsistencies in the material's behavior.

5. How does the amount of doping affect the mobility of resonating valence bonds?

The amount of doping can greatly affect the mobility of resonating valence bonds. Too little doping may not have a significant impact on the bonds' mobility, while too much doping can cause the material to become unstable. It is important to carefully control the amount of doping to achieve the desired level of mobility without compromising the material's properties.

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