Author Topic: energy independent kappa value in Complex band structure of HfO2  (Read 3551 times)

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Offline zmisha

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Dear Sir/Madam,
 
        I did complex band structure calculation of HfO2 orthorhombic phase.
        I got energy independent kappa curve, which has small value as in attachment(hfo2_complex.tif). 
        However, I am expecting kappa curve with an elliptic shape as in attachment(WSe2_complex.tif) from a reference paper. "Monolayer Transition Metal dichalcogenide channel-based tunnel transistor." R. K. Ghosh et al.
 
        I do not really understand where is this energy independent kappa curve from or what is the meaning of it. 
        Could you please give me some comments?
   
       

Offline Daniele Stradi

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Hi,
can you post the structure? Why would you expect the same features in the complex band structure for two different materials?
Regards,
Daniele

Offline zmisha

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Hi,
    Attachment is the HfO2 phase structure.
    I guess what I really want it  where the energy independent kappa curve comes from. Or I am not sure how to explain the physics behind it.

    Based on the tutorial, the imaginary bands are connected with the real band. But how the energy independent kappa curve connected with the real band?

Offline Petr Khomyakov

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I guess the kappa still depends on the energy, but the dependence is just rather weak. To see a connection of the corresponding imaginary bands to real bands you may need to plot the band structure over much larger energy range.

The difference between the HfO2 and WSe2 complex band structures is very likely due to a larger band gap of HfO2 compared to that of WSe2, meaning that the HfO2 imaginary bands (or in other words, evanescent states) are more localized in some way.

I would like to notice that these states are not real physical states in a perfect bulk material such as HfO2.  The evanescent states may however couple, for example, to metal electrode states if a HfO2 dielectric spacer is sandwiched between two metal electrodes. To understand this, you may think of a simple 1D barrier problem, when plane-wave states are matched to exponentially-decaying states at the two barrier edges, for a given energy (which is below the top of the barrier indeed). 

Offline zmisha

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Thanks for your help.