Mailman 3 December 2014 - Kwant-discuss

How the spin is positioned in the Smatrix?
by Qingtian Zhang 06 Mar '22

06 Mar '22

Dear all, I am trying square lattice with spin-orbit coupling and Zeeman splititng just like the example of Tutorial 2.3.1. Now I want to get the spin-dependent conductance：Guu,Gud,Gdu,and Gdd, where "u" indicates up spin, d indicates down spin. We can have the scattering matrix through Smatrix=kwant.smatrix(sys, energy), but how the spin is positioned in the scattering matrix? I have checked some simple cases, it seems the Smatrix is organized like this: | r t | S= | t' r' | but how the spin is included? Thanks in advance. Qingtiian Zhang The code is: import kwant from matplotlib import pyplot from numpy import matrix import tinyarray sigma_0 = tinyarray.array([[1, 0], [0, 1]]) sigma_x = tinyarray.array([[0, 1], [1, 0]]) sigma_y = tinyarray.array([[0, -1j], [1j, 0]]) sigma_z = tinyarray.array([[1, 0], [0, -1]]) sys=kwant.Builder() lat=kwant.lattice.square() a=1 t=1.0 alpha=0.5 e_z=0.08 W=2 L=2 sys[(lat(x, y) for x in range(L) for y in range(W))] = \ 4 * t * sigma_0 + e_z * sigma_z # hoppings in x-direction sys[kwant.builder.HoppingKind((1, 0), lat, lat)] = \ -t * sigma_0 - 1j * alpha * sigma_y # hoppings in y-directions sys[kwant.builder.HoppingKind((0, 1), lat, lat)] = \ -t * sigma_0 + 1j * alpha * sigma_x #### Define the left lead. #### lead = kwant.Builder(kwant.TranslationalSymmetry((-a, 0))) lead[(lat(0, j) for j in xrange(W))] = 4 * t * sigma_0 + e_z * sigma_z # hoppings in x-direction lead[kwant.builder.HoppingKind((1, 0), lat, lat)] = \ -t * sigma_0 - 1j * alpha * sigma_y # hoppings in y-directions lead[kwant.builder.HoppingKind((0, 1), lat, lat)] = \ -t * sigma_0 + 1j * alpha * sigma_x #### Attach the leads and return the finalized system. #### sys.attach_lead(lead) sys.attach_lead(lead.reversed()) kwant.plot(sys) sys=sys.finalized() print "Hamiltonian=" print sys.hamiltonian_submatrix() Smatrix=kwant.smatrix(sys, energy=3.) print "The scattering matrix=" print matrix.round((Smatrix.data),2) print "T=",(Smatrix.transmission(1, 0))

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How to caculate hall resistance
by ZHANG Bing 12 Sep '21

12 Sep '21

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

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About cubic lattice hopping
by ANANT 25 Dec '14

25 Dec '14

hello ! I am trying to simulate a cubic lattice and I want to write hopping without using neighbors() function,as I am writing different hopping parameters in different directions my lattice is this: lat = kwant.lattice.general([(1,0,0),(0,1,0),(0,0,1)],[(0,0,0)]) def make(a = 4 ,b = 5, c= 1,t=1,delta = 1): def cube(pos): x,y,z = pos return 0<=x<=a and 0<=y<=b and 0<=z<=c sys = kwant.Builder() sys[lat.shape(cube,(0,0,0))] = -4* t sys[lat(0,0,0),lat(0,0,1)] = -t return sys this code is showing me an error: TypeError: 'Polyatomic' object is not callable

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Announcement: an open online course on topology in condensed matter.
by Anton Akhmerov 15 Dec '14

15 Dec '14

Hi everyone, Kwant is going to be one of the main tools in an online course that I would like to announce. The course topic is topological phenomena in condensed matter, and it will start 9 Feb 2015, check it out here: http://tiny.cc/topocm ! The course will be hosted on EdX platform, and will be fully open and free. Our aim is to provide an introduction to the exciting theoretical and experimental developments of the last decade in a way which would make it accessible to non-experts, experimentalists, or anyone with basic understanding of condensed matter. We are going to provide the participants an understanding of the key concepts in topology, follow current research, and perform research on their own. With best regards, the course team: Anton Akhmerov, Jay Sau, Bernard van Heck, Sebastian Rubbert, and Rafał Skolasiński

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Fw: Kwant codes
by Hossain Iztihad 14 Dec '14

14 Dec '14

I need codes of double gate MOSFET & Resonent tunnling diode so that i can do some revese engineering. I am a beginner of kwant package & badly need this help. thanks in advance.The structure of my device is uploaded below:Best RegardsHossain Iztihad

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About bans structure for 3d
by ANANT 09 Dec '14

09 Dec '14

hello everyone. I am trying to plot r=the band structure of 3 d structure .but getting an error.Please tell me how to deal with 3 d structures?my code is this: import kwant from matplotlib import pyplot import math import numpy as np import cmath lat = kwant.lattice.general([(0, 0.5, 0.5), (0.5, 0, 0.5), (0.5, 0.5, 0)], [(0, 0, 0), (0.25, 0.25, 0.25)]) a, b = lat.sublattices def make_cuboid(a=2, b=2, c=2): def cuboid_shape(pos): x, y, z = pos return 0 <= x < a and 0 <= y < b and 0 <= z < c sym = kwant.TranslationalSymmetry(lat.vec((-1,-1,-1))) sys = kwant.Builder(sym) sys[lat.shape(cuboid_shape, (0, 0, 0))] = None sys[lat.neighbors()] = None return sys sys = make_cuboid() sys = sys.finalized() kwant.plotter.bands(sys, momenta= np.linspace(-5,5,10000),show=False) pyplot.xlabel("momentum [(lattice constant)^-1]") pyplot.ylabel("energy [t]") pyplot.show() The error is :TypeError: a float is required

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About graphene dispersion file
by ANANT VIJAY 06 Dec '14

06 Dec '14

Good morning Sir, I am not able to open the file you sent me about 6 dirac points of graphene dispersion.Please could you send me the .py file of it. Thank you for your kind help. ANANT VIJAY VARMA M.Tech. STUDENT CENTER FOR CONVERGING TECHNOLOGIES UNIVERSITY OF RAJASTHAN JAIPUR

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About dispersion relation
by ANANT 05 Dec '14

05 Dec '14

Is there any way in KWANT that I can plot a 3-d graph of dispersion relation?In the tutorial it is given that the infinite system is quasi 1-d system.that means is it only giving values for Kx momentum.I guess not. I guess it is the values of energies for momentum K = -sqrt(Kx*Kx + Ky*Ky) and K = +sqrt(Kx*Kx + Ky*Ky).Please explain.

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Contour plot of the conductance
by Lee Kwok-Long 05 Dec '14

05 Dec '14

Dear all, I am new to Kwant and Python. I want to consider a contour plot of the conductance as a function of energy and the well depth for Tutorial 2.3.2. The contour plot is similar to the one on the homepage in “Conductance of a Corbino disk in a quantum Hall regime”, but the codes are not shown in the tutorials. I want to learn this example since it will be more flexible to consider the effects of the device parameters. I want to output the results into a .txt file with the energy in the first column, well depths in the second column, conductance in the third column, so I can plot the contour by origin. Tutorial 2.3.2 is a simple example to consider the contour plot, and we may only need to do small changes. The codes for Tutorial 2.3.2 areattached. Could you help me? Thanks in advance. Kwok-Long Lee

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About leads for transmission calculation
by ANANT 01 Dec '14

01 Dec '14

hello everyone, I am calculating transmission using smatrix.transmission() function .my system has four leads in a square lattice structure.Please tell me about the matrix entries in this function.like smatrix.transmission(1,2) and smatrix.transmission(2,1) are showing differrent spectrum.How this transmission function is reading these lead numbers.My code is this: # -*- coding: utf-8 -*- # <nbformat>3.0</nbformat> # <codecell> import kwant from matplotlib import pyplot from cmath import exp import numpy as np # <codecell> def hopping(sitei, sitej, phi, salt): xi, yi = sitei.pos xj, yj = sitej.pos return exp (-0.5j*phi*(xi-xj)*(yi + yj)) a=1 lat =kwant.lattice.square(a) def make(a=60,b=20,t=1): def square(pos): x,y =pos return 0<=x<=a and 0<=y<=b #def hop(sit1,site2,B=1): #y = sit1.pos[1] #print y #return -t * exp(-1j * B * y) sys = kwant.Builder() sys[lat.shape(square,(0,0))] = 4*t #sys[kwant.builder.HoppingKind((1,0),lat,lat)] = hopping #sys[kwant.builder.HoppingKind((0,1),lat,lat)] = -t sys[lat.neighbors()] = hopping #del sys[lat(12,9)] sym1 = kwant.lattice.TranslationalSymmetry(lat.vec((0,1))) def shape1(pos): x,y = pos return 0<=x<=a lead0 = kwant.Builder(sym1) lead0[lat.shape(shape1,(0,0))] = 4*t lead0[lat.neighbors()] = hopping sys.attach_lead(lead0) sys.attach_lead(lead0.reversed()) sym0 = kwant.lattice.TranslationalSymmetry(lat.vec((-1, 0))) def shape(pos): x,y = pos return 0<=y<=b lead1 = kwant.Builder(sym0) lead1[lat.shape(shape,(0,0))] = 4*t lead1[lat.neighbors()] = hopping sys.attach_lead(lead1) sys.attach_lead(lead1.reversed()) return sys.finalized() energy = .16 def plot_condu(sys,phis): data = [] for phi in 1/phis: print phi smatrix = kwant.smatrix(sys, energy,args=[phi, ""]) data.append(smatrix.transmission(2,1)) pyplot.figure() pyplot.plot(phis,data) pyplot.show() # <codecell> def main(): sys = make() #kwant.plot(sys) plot_condu(sys ,phis = np.linspace(1,100,100)) # <codecell> if __name__ == '__main__': main() # <codecell>

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