[Wien] optical conductivity or electronic conductivity?

[shamik chakrabarti]

Dear Nazma ,

                   Thank you very much for your clarification and for giving
me a reference on optical properties.

2009/10/31 Nazma Ikram <nazmaikram at hotmail.com>

>  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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