[Kwant] Calculating valley polarized conductances using Kwant

[Kevin Ryczko]

Dear community,

I would like to calculate the valley polarized conductance for a graphene 
nanoribbon with 2 leads (let’s say in the x-direction). My current approach is 
this:

1) Get the S-matrix for a certain energy
2) Find the indices of the modes with positive velocities
3) Separate these modes by positive and negative momenta
4) Get the sub matrix from the S-matrix
5) Sum the transmission coefficients for positive and negative momenta

The code below illustrates these 5 steps:

import progressbar
def valleyPolarizability(syst, energies, lead_start=0, lead_end=1):
    KPs = []
    Ks = []
    bar = progressbar.ProgressBar()
    for energy in bar(energies):
        smatrix = kwant.smatrix(syst, energy, params={'phi': phi})
        positives = np.where(smatrix.lead_info[lead_start].velocities >= 0)[0]
        momentas = smatrix.lead_info[lead_start].momenta[positives]
        K_prime_indices = np.where(momentas < 0)[0]
        K_indices = np.where(momentas >= 0)[0]
        submatrix = smatrix.submatrix(lead_end, lead_start)
        K_prime_T = np.absolute(np.sum(submatrix[:, K_prime_indices]))**2
        K_T = np.absolute(np.sum(submatrix[:, K_indices]))**2
        KPs.append(K_prime_T)
        Ks.append(K_T)
    return KPs, Ks

Could someone please let me know if this is the correct approach? Will the 
K_prime_indices and K_indices have the correct indexing in the sub matrix?

Thanks,
Kevin Ryczko