QuantumATK Forum

QuantumATK => General Questions and Answers => Topic started by: jchang on January 28, 2020, 13:38

Title: Unit of Transmission
Post by: jchang on January 28, 2020, 13:38

Hi

I have question about the unit of transmission which we get from the transmission calculation.
Let's say that we have periodic structure in transverse direction like an example below.
https://docs.quantumatk.com/tutorials/transmission_gr_mos2/transmission_gr_mos2.html
And I want to calculate current/width [A/um].
Then, the transmission that I get from the calculation in the above example should be divided by the width of real space unit cell. (of course, I need to multiply it with e^2/h)
Am I doing right?
I just want to confirm the dimension of the transmission that I get from quantum ATK.

Thanks.
jiwon

Title: Re: Unit of Transmission
Post by: Petr Khomyakov on January 30, 2020, 13:03

Transmission coefficient is an unitless quantity, being defined per a lateral unit cell, i.e., doubling the lateral unit cell would double the transmission value, just because the cross section is doubled, so more current can path through the conductor.

In QuantumATK, transmission can be defined, e.g., as total (sum) transmission or transmission per spin. The total one is just a sum of the transmission coefficients for spin up and down.
One can also compute the current from the Transmission Spectrum, see the manual at https://docs.quantumatk.com/manual/Types/TransmissionSpectrum/TransmissionSpectrum.html, where you may also find different options on how transmission can be computed.

Note that the current is computed per lateral unit cell as well, so you have to divide it by the cross section (lateral unit cell) area to get the current density, if needed.