Dear Sir,
I am a PhD student of Hong Kong University of Science and Technology. I
want to use KWANT to caculate Hall resistance of a Hall bar structure.We
can get the conductance between 6 electrodes, but how to get hall
resistance? Can you give me some help? Thank you very much.
Best Regards,
Zhang Bing
Hi,
I want to add two leads on left instead. I have attached two leads and try
to find conductance and compare with just one lead on left. The results for
two leads and just one lead is not same. Can you help me what I am doing
wrong here?
I have attached my code here.
import kwant # Recursive green function method
import numpy as np # Module with advanced math commands
from matplotlib import pyplot
from numpy import sqrt
from math import *
#======================================================================
# Define the shape -------------------
#======================================================================
def wv_shape(pos):
x, y = pos
return (np.abs(2.0*x)<=L)&(np.abs(y)<W1/2.0)
#----------------------------------------------------------------------
a = 1; # Lattice constant
t = 1; # Coupling between sites
E0L = 0*t # On-site potential in the lead
L = 18; # Length of the
W1 = 90; # Width on the left
# Define geometry
--------------------------------------------------------------------------
sys0 = kwant.Builder()
lat = kwant.lattice.square(a)
#--------------------------------------------------------------------------------------------
# Define onsite energies and couplings
----------------------------------------------------
sys0[lat.shape(wv_shape,(0,0))] = E0 # To make all sites the same
sys0[lat.neighbors()] = t
#--------------------------------------------------------------------------------------------
# Left lead
----------------------------------------------------------------------------------
left_lead1 = kwant.Builder(kwant.TranslationalSymmetry([-1,0])) # The
lead goes to minus infinity
left_lead2 = kwant.Builder(kwant.TranslationalSymmetry([-1,0])) # The
lead goes to minus infinity
left_lead1[(lat(0,y) for y in range(int(-W1/2+1),0))] = E0L
left_lead2[(lat(0,y) for y in range(0,int(W1/2)))] = E0L
left_lead1[lat.neighbors()] = t #
Couplings in the lead
left_lead2[lat.neighbors()] = t #
Couplings in the lead
sys0.attach_lead(left_lead1);
sys0.attach_lead(left_lead2);
#--------------------------------------------------------------------------------------------
# Right lead
---------------------------------------------------------------------------------
right_lead = kwant.Builder(kwant.TranslationalSymmetry([1,0])) # The lead
goes to plus infinity
right_lead[(lat(0,y) for y in range(int(-W1/2+1),int(W1/2)))] = E0L
right_lead[lat.neighbors()] = t #
Couplings in the lead
sys0.attach_lead(right_lead);
#---------------------------------------------------------------------------------------------
sys = sys0.finalized()
kwant.plot(sys); # Plots the
shape
def plot_conductance(sys, energies):
data = []
for energy in energies:
smatrix = kwant.smatrix(sys, energy)
data.append(smatrix.transmission(2, 0)+smatrix.transmission(1,2) )
#transmission from left 2 leads to right lead
pyplot.figure()
pyplot.plot(energies, data)
pyplot.xlabel("energy [t]")
pyplot.ylabel("conductance [e^2/h]")
pyplot.show()
energies=[-3+i*0.02 for i in range(100)]
plot_conductance(sys,energies)
Hello all,
Is it posible to calculate the Hall mobility in a closed system using kwant?
--
Dr. Eleni Chatzikyriakou
Computational Physics lab
Aristotle University of Thessaloniki
elchatz(a)auth.gr - tel:+30 2310 998109
Hello,
I have just started using kwant, and I am trying to write a code
excerpt that saves a figure of my system, but I just get a blank 3-D
space. The code is the following, as taken by the TBModels website:
-----------------------------------------------------------------
import kwant
import tbmodels
import wraparound
import numpy as np
import scipy.linalg as la
import matplotlib
matplotlib.use('agg')
import matplotlib.pyplot as plt
model = tbmodels.Model.from_wannier_files(
hr_file='..._hr.dat',
wsvec_file='..._wsvec.dat',
xyz_file='..._centres.xyz',
win_file='....win'
)
lattice = model.to_kwant_lattice()
wire = kwant.Builder()
def shape(p):
x, y, z = p
return -20 < x < 20 and -5 < y < 5 and -5 < z < 5
wire[lattice.shape(shape, (0, 0, 0))] = 0
model.add_hoppings_kwant(wire)
fig = plt.figure()
ax = plt.subplot()
ax = kwant.plot(wire)
plt.savefig('wire.png')
----------------------------------------------------------------------------------------
If anyone knows whether the problem is with the system or with the
plotting it would be greatly appreciated.
Regards
--
Dr. Eleni Chatzikyriakou
Computational Physics lab
Aristotle University of Thessaloniki
elchatz(a)auth.gr - tel:+30 2310 998109
Dear all,
sorry, this might be more a matplotlib question than a kwant question.
Below is a minimal code which produces two figures, each showing a different dataset: a current in the scattering region due to a wavefunction in a lead.
I would like to combine the two into a single plot, distinguishing the two datasets by e.g. different colormaps (and two different colorbars).
Any ideas?
Thanks a lot,
Tibor
______________________________________
import kwant
from math import pi, sqrt
from cmath import exp
import numpy
from matplotlib import pyplot as plt
#some parameters
t=1
L=30
W=30
EF=0.1
phi=0.01
def hopping(sitei, sitej, phi):
xi, yi = sitei.pos
xj, yj = sitej.pos
return -t*exp(1j*2*pi*phi*2/sqrt(3)*(yj - yi)*(xi + xj)/2)
def make_system():
lat = kwant.lattice.general([(sqrt(3)*1/2, 1/2), (0, 1)],
[(0, 0), (1/(2*sqrt(3)),1/2)], norbs=1)
def central_region(pos):
x, y = pos
return abs(x) < L/2 and abs(y) < W/2
def lead0_shape(pos):
x, y = pos
return abs(x) < L/2
#scattering region
sys = kwant.Builder()
sys[lat.shape(central_region, (0,0))] = -EF
sys[lat.neighbors()] = hopping
sys.eradicate_dangling()
#leads
sym = kwant.TranslationalSymmetry(lat.vec((0,1)))
lead0 = kwant.Builder(sym)
lead0[lat.shape(lead0_shape, (0,0))] = -EF
lead0[lat.neighbors()] = hopping
lead0.eradicate_dangling()
lead1=lead0.reversed()
return sys, lead0, lead1
sys, lead0, lead1 = make_system()
sys.attach_lead(lead0)
sys.attach_lead(lead1)
sysf = sys.finalized()
wf = kwant.wave_function(sysf, energy=0.0001, params=dict(phi=phi))
J = kwant.operator.Current(sysf)
psi1 = wf(0)[0]
e_current1 = J(psi1, params=dict(phi=phi))
psi2 = wf(1)[0]
e_current2 = J(psi2, params=dict(phi=phi))
kwant.plotter.current(sysf, e_current1, cmap="OrRd", colorbar=True, show=False)
ax = plt.gca()
plt.colorbar(ax.get_children()[-2], ax=ax)
kwant.plotter.current(sysf, e_current2, cmap="Blues", colorbar=True, show=False)
ax = plt.gca()
plt.colorbar(ax.get_children()[-2], ax=ax)
plt.show()
