sahu.aji...@gmail.com wrote:

> 1. In the example of KWANT, there is a conductance vs Energy plot. In
> this plot, the unit of Energy is mentioned as [t]. what does
> t signify? is it in eV?

Kwant does not impose any unit of energy.  The unit of energy is
whatever the user used when defining the Hamiltonian.  So, if you
defined your Hamiltonian using eVs your unit of energy will be eVs, if
you are using Joules, it will be Jules, if you use... calories, it will
be in calories.

In the first tutorial example, the hopping integral (= t) has the
numerical value of 1.  This can be interpreted as using t as unit of
energy.

Let’s say we switch to eVs and set t = 2.8 eV.  Now all the energy
values will be multiplied by 2.8 compared to when t was 1.  But
considered in units of t (and thus divided by 2.8), the numerical values
would be the same as before.  So, it’s handy to set t = 1 and simply say
that energy is in units of t (whatever t actually is).

> 2. In the band structure of zig-zag graphene lead, there are upper and
> lower parts in the band structure. which one is the conduction band?
> I'm attaching a figure for 2nd question.

Please use proper email attachments.  Future readers of your message
should be able to see your figure even after you have removed it from
your google drive.

Zig-zag graphene ribbons are metallic, so there is no gap and no valence
and conduction band.  Check out
https://en.wikipedia.org/wiki/Graphene_nanoribbon#Electronic_structure.

Cheers
Christoph

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