sahu.ajit92@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