Mailman 3 May 2015 - 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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New instructions for Windows installation
by Michael Wimmer 15 Jan '16

15 Jan '16

Dear kwant users, we have posted new instructions for installing kwant on Windows on the kwant website: http://www.kwant-project.org/install The old instructions do not work any more, as the format of the python packages on Christoph Gohlke's webpage have changed. Best regards, the kwant team

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Package for ubuntu vivid
by David Abergel 17 Sep '15

17 Sep '15

Hi all, firstly, thanks so much for your work in developing and maintaining kwant. Hugely appreciated. Is there any chance you could package it for {,k,x}ubuntu 15.04? I tried installing kwant in that linux today, using the 14.10 package, and I am getting a bunch of errors from Tkinter and matplotlib when I use kwant's inbuilt plotter. Many thanks for your help David

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Re: [Kwant] suggestion
by Sergey 12 Jul '15

12 Jul '15

Dear Christoph, I use the following construction to connect the incommensurate lattices: lat_e (graphene) and lat_e1 (square) for x in list(lat_e1.shape(rectangle1, (0, 0))()): for neighbour in lat_e.sublattices[0].n_closest(x.pos): sys[(x, lat_e.sublattices[0](*neighbour))] = t01 for neighbour in lat_e.sublattices[1].n_closest(x.pos): sys[(x, lat_e.sublattices[1](*neighbour))] = t01 I hope it's clear why I want to improve n_closest Probably I can do that myself. The above construction may indeed be in the core of readymade function to connect the two lattices. Best wishes, Sergey

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Re: [Kwant] Kwant-discuss Digest, Vol 18, Issue 1
by Lee Kwok-Long 23 May '15

23 May '15

Dear Joe, Thanks, it is very useful for me. I want to know more about how the transmission is related to the wave vector kx, because I want to calculate the transmission contributed from some scale like kx=0~pi. So, how can i know the wave vector for "2" in S10[3, 2] ? I tried "modes = Smatrix.lead_info", it seems that it does not give the kx information. I can take graphene as an example, we have two valleys K and K' in graphene. Since the wave vectors kx for the two valleys are different, we can calculate the transmission contributed from K valley and K' valley separately, but of course we need to know "transmission-mode-kx" first. Maybe this can be easily solved in another way. Kwok-Long Lee On Fri, Feb 6, 2015 at 8:03 PM, <kwant-discuss-request(a)kwant-project.org> wrote: > Send Kwant-discuss mailing list submissions to > kwant-discuss(a)kwant-project.org > > To subscribe or unsubscribe via the World Wide Web, visit > https://mailman-mail5.webfaction.com/listinfo/kwant-discuss > or, via email, send a message with subject or body 'help' to > kwant-discuss-request(a)kwant-project.org > > You can reach the person managing the list at > kwant-discuss-owner(a)kwant-project.org > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of Kwant-discuss digest..." > > > Today's Topics: > > 1. Transmission of each propagating mode (Lee Kwok-Long) > 2. Re: Transmission of each propagating mode (Joseph Weston) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Fri, 6 Feb 2015 16:43:23 +0800 > From: Lee Kwok-Long <kwoklonglee(a)gmail.com> > To: kwant-discuss(a)kwant-project.org > Subject: [Kwant] Transmission of each propagating mode > Message-ID: > < > CAMzfLzK0z7uFZGB54o71i8yr0hb2hf1D9GXxEhckubFYuQC5_g(a)mail.gmail.com> > Content-Type: text/plain; charset="utf-8" > > Dear all, > I want to calculate the transmission of each propagating mode separately, > but I do not know how the propagating modes are related to the scattering > matrix. For example, we can read from the bandstructure and find a mode at > E=0.2，kx=0.95pi, how to find the transmission for this mode. Or, we have > the transmission and how to find the contributions from each mode? Thanks > in advance! > Kwok-Long Lee >

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Kwant.greens_function
by Weiyuan Tong 18 May '15

18 May '15

Dear all, Since I used NEGF in my previous study, I want to use Green's function in Kwant. I have tried a simple Kwant program to check my understanding of "kwant.greens_function" and "lead.selfenergy(energy)", but it gives wrong results. I used Fisher-Lee relation to calculate the conductance: G = kwant.greens_function(sys, energy) Gr=G.submatrix(1,0) # r indicates retarded Ga=conj((Gr).T) # a indicates advanced Sigma_Lr =flead0.selfenergy(energy) #r indicates retarded Sigma_La =conj((Sigma_Lr).T) #a indicates advanced Sigma_Rr =flead1.selfenergy(energy) Sigma_Ra =conj((Sigma_Rr).T) Gamma_in =1j*(Sigma_Lr-Sigma_La) Gamma_out=1j*(Sigma_Rr-Sigma_Ra) #TM=Gamma_out*Gr*Gamma_in*Ga TM=Np.dot(Np.dot(Np.dot(Gamma_out,Gr),Gamma_in),Ga) #Fisher-Lee relation data.append(real(Np.trace(TM))) #Fisher-Lee relation Do I do I misunderstand anything? Can you please find my mistakes? My Kwant program code is attached at the end of this email. Thanks in advance! Best wishes, Weiyuan Tong

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Transmission amplitudes with same propagating modes
by Lee Kwok-Long 17 May '15

17 May '15

Dear authors, I am sorry that I did not express it clear in my last email. For a 4 lead system, we have T30=smatrix.submatrix(3,0), T20=smatrix.submatrix(2,0) they all include all the propagating modes. What I want is: for each propagating mode like kx=2.9，we have the elements T30(3,3) and also the elements in T20. If T30 and T20 are all arranged by propagating modes, it may be very easy, T30(i,i) and T20(i,i) are for the same propagating mode. So, is there a method to output T30(i,j) and T20(i,j) with the same propagating mode? Regards, Kwok-Long Lee

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LDOS for tunneling conductance in superconductor
by Amit 15 May '15

15 May '15

Hi I want to calculate local density of states for tunneling into a spinful superconductor. I have followed the example in the tutorial to set up superconducting transport problem: http://kwant-project.org/doc/1.0/tutorial/tutorial5 I was wondering if I could find the LDOS at a given site by first seperating particle and hole contributions with: a,b = np.split(kwant.ldos(sys,l),2) And then add particle and hole contributions with np.add(a,b) and sum over the spin parts with: np.sum(np.add(a,b).reshape(-1,2),axis=1) thanks Amit

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About the Green's function
by Weiyuan Tong 13 May '15

13 May '15

Dear authors, I found a description for the greens_function in the Kwant document: "This function can be used to calculate the conductance and other transport properties of a system", so, we can also use the fisher-lee relation to calculate the conductance in Kwant? I read from Joe's reply email that the Green's function can be used like: G = kwant.greens_function(sys, energy) G.submatrix(1, 0) # from lead 0 to lead 1 this is the retarded Green's function? So the advanced Green's function is G'=[G]+? How to calculate the self-energy for lead 0 and lead 1? Since there is no example in the tutorial, can you give us some suggestions or simple examples? Best wishes, Weiyuan Tong

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