Dear kwant users

I'm trying to calculate magnetic field dependent conductance of a system. For this I used the scattering matrix and adding temperature dependence
by multiplying the transmission value by the derivative of the fermi-dirac function. Because of the results I got, I'm not sure if this is the right way of doing it.

Thank you very much

Best regards
Simon

Code:

fluxes = np.linspace(0, 5, 100)

def make_system(a=1, t=1.5, w=15, d=30):
lat = kwant.lattice.square(a)
syst = kwant.Builder()

def onsite(site, U0, salt):
return U0 * (uniform(repr(site), repr(salt)) - 0.5) +  4*t

syst[(lat(x, y) for x in range(w) for y in range(d))] = onsite

def hopping(site_i, site_j, phi):
xi, yi = site_i.pos
xj, yj = site_j.pos
if yi == yj:
return -t
if xi == xj:
return -0.001 * t * exp(-0.5j * phi * (xi + xj) * (yi - yj))

syst[lat.neighbors()] = hopping

lead[(lat(j, 0) for j in range(w))] = 4 * t

return syst

def plot_conductance(syst):
temp = 0.01
w=15
d=30
U0=0
salt = 0.2
phis = np.linspace(0, (2 * pi / w) * 5, 100)
count = 0
values = []
for phi in phis:
count += 1
ham_mat = syst.hamiltonian_submatrix(params=dict(phi=phi, U0=U0, salt=salt), sparse=True)
evals = np.real(np.sort(np.linalg.eigvals(ham_mat.todense())))
EF = evals[int(len(evals) / 2)]
liste = []
for k in range(0,len(evals)):
energy = evals[k]

if EF-temp <= energy <= EF+temp:
df = np.real(exp((energy - EF) / temp) / (temp * (exp((energy - EF) / temp) + 1) ** 2))
Smatrix = kwant.smatrix(syst, energy, params=dict(phi=phi, U0=U0, salt=salt))
liste.append(Smatrix.transmission(0,1)*df)
val = sum(liste)/(len(liste))
values.append(val/(w*d))
print(count)

plt.plot(fluxes,values, label = w)
plt.grid(True)
plt.title("Conductance eqhop temp=0.1")
plt.legend()
plt.ylabel("G_[G_0]")
plt.xlabel(r'$\phi [2\pi / L]$')
plt.show()

def main():
syst = make_system()
syst = syst.finalized()
plot_conductance(syst)

if __name__ == "__main__":
main()