[Wien] optical conductivity or electronic conductivity?

[Nazma Ikram]

Please be clear about two things:

1. Electrons

2.Photons.

 

When we talk about optical properties such as transparent, reflecting  or an opaque material ,we are talking about those photons which correspond to the optical region of the spectrum.

 

When we consider electronic conduction, we are talking about electrons.

 

When we calculate the band structure of a crystalline solid, we get regions of electron energy separated by energy gaps which arise due to the periodicity of the crystal.

 

We can excite an electron from the valence band to the conduction band in a semiconductor by bombarding photons on the crystal such that these photons have energy larger than the band gap. That is we have photoconductivity.

 

If you look at the mathematical expression for electronic conductivity, you will find that there is 'difference of the  gradient of energyof the conduction & the valence band' in the denominator.When these two gradients are equal, there is resonance & hence a peak.


 Read the first few chapters of the book on 'The optical properties of solids' by FOX.  It has simple mathematics & gives clear concepts.

 

All the best. 

 

 


Date: Fri, 30 Oct 2009 22:18:55 +0530
From: shamikphy at gmail.com
To: wien at zeus.theochem.tuwien.ac.at
Subject: Re: [Wien] optical conductivity or electronic conductivity?

Dear Nazma,

                   Thank you very much for your reply. To further clarify my doubt I am asking one more question. If we get one peak in the optical (i.e. electronic) conductivity spectrum does it mean that at that frequency more photons will be absorbed giving high value of its absorbtance and also high value of electronic conductivity i.e. does it mean at that frequency the material is electronically conducting (transparent) but optically opaque?...

Shamik Chakrabarti


2009/10/30 Nazma Ikram <nazmaikram at hotmail.com>



The word optical here means that e m radiations in the frequency range corresponding to optical spectum are incident  on the semiconductor, causing transition of electrons (hence electronic) from the valence to conduction band. 


Date: Thu, 29 Oct 2009 10:26:29 +0530
From: shamikphy at gmail.com
To: wien at zeus.theochem.tuwien.ac.at
Subject: [Wien] optical conductivity or electronic conductivity?





Dear wien2k users,
 
         By calculating  dielectric tensor we can calculate electronic conductivity. I have calculated dielectric tensor and from which I have also deduced electronic conductivity sigma by following the relation:

     Im.epsilon=sigma/omega

where sigma=electronic conductivity
and omega=angular frequency of the EM wave (energy*2pi/h)

Now In file case.absorpup (or dn) we can find the data for optical conductivity in unit 1/(ohm.cm). But when I plot optical and electronic  conductivity separately I have found they are exactly the same. Then my question is

Q: whether we find optical or electronic conductivity in the file case.absorpup?

P.S. optical and electronic conductivity are not the same thing!...glass is electronically insulating but optically conducting (transparent) material.
 
 



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