Mailman 3 February 2015 - Kwant-discuss

How the spin is positioned in the Smatrix?
by Qingtian Zhang March 6, 2022

March 6, 2022

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))

3 3

How to caculate hall resistance
by ZHANG Bing Sept. 12, 2021

Sept. 12, 2021

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

4 3

New instructions for Windows installation
by Michael Wimmer Jan. 15, 2016

Jan. 15, 2016

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

3 3

Re: [Kwant] Kwant-discuss Digest, Vol 18, Issue 1
by Lee Kwok-Long May 23, 2015

May 23, 2015

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 >

2 3

Bug report
by Bas Nijholt March 3, 2015

March 3, 2015

I’ve found a bug in add_site_family(), the input for other_vectors should be a list, but I used a tulpe, the error message I got is not correct. Code: lat = kwant.lattice.general([(1, 0), (sin_30, cos_30)], [(0, 0), (0, 1 / sqrt(3))]) a, b = lat.sublattices sym_lead = kwant.TranslationalSymmetry(lat.vec((1, 0))) sym_lead.add_site_family(a, other_vectors=(1, -2)) Error message: --------------------------------------------------------------------------- ValueError Traceback (most recent call last) <ipython-input-73-c9cfa5f61ce2> in <module>() 4 sym_lead = kwant.TranslationalSymmetry(lat.vec((1, 0))) 5 ----> 6 sym_lead.add_site_family(a, other_vectors=(1, -2)) /usr/local/lib/python2.7/site-packages/kwant/lattice.pyc in add_site_family(self, fam, other_vectors) 572 573 if np.linalg.matrix_rank(m) < num_vec: --> 574 raise ValueError('other_vectors and symmetry periods are not ' 575 'linearly independent.') 576 ValueError: other_vectors and symmetry periods are not linearly independent.

6 6

A question about the tutorial
by Даниил Антоненко Feb. 28, 2015

Feb. 28, 2015

Hello! I now learn to use kwant and I can't get one thing. In the first example from the tutorial we can see steps of conductance. But the energies, at which the jumps occur do not have n^2 dependence as should be for the levels of perpendicular quantization in the quantum box with zero boundary conditions. I took a longer stripe, but it didn't help. Why it is so? Yours Sincerely, Daniel.

2 1

Re: [Kwant] Data extract numerically
by Anton Akhmerov Feb. 19, 2015

Feb. 19, 2015

Dear George, To get a numpy array with the coordinates of each site, you can use np.array([sys.pos(i) for i in range(sys.graph.num_nodes)]) for a finalized system. It is up to you to transform this into any other desired format. Best, Anton On Thu, Feb 19, 2015 at 10:58 PM, George Yumnam <georgeyumnam(a)gmail.com> wrote: > Dear Prof. Anton, > > For a simple case, say after generating a Graphene sheet. I can plot it > using kwant.plot(sys) and I can see the structure on the graphic window but > I am not able to access this structure in any other way. I would like to > obtain positions of each carbon atoms in a file so that it can be visualized > in softwares like Vesta and Crystalmaker. So the preferred format is ".xyz" > format, something like the one I have attached with this email. I understand > that kwant is a package to perform quantum transport numerically. But I want > to access the structures, created before the calculations, for analyzing if > it is the desired structure for my problem. > > Sincerely, > George Yumnam

1 0

Data extract numerically
by George Yumnam Feb. 19, 2015

Feb. 19, 2015

Hello everyone, I am new in using kwant and I have started creating some structures. I want to extract these structures numerically for use in other visualization software life vesta and crystalmaker. I have tried searching for ways to do this but unfortunately no-one have discussed this. So kindly, help me out in extracting this data. Thank you in advance. Sincerely, George Yumnam

1 0

outputing Hamiltonian with superconductivity
by HY Feb. 13, 2015

Feb. 13, 2015

If I initialize a finite system with superconductivity using 2.6.2, finalize it, and output the Hamiltonian using sys.finalized().hamiltonian_submatrix() I have no clue how the sites are ordered. It is neither grouped with particle/hole nor with sites. For example with Delta=1, mu=2, t=5, L=3, the output is [[ 3.+0.j 0.+0.j 5.-0.j 0.+0.j 1.-0.j 0.+0.j] [ 0.+0.j -3.+0.j 0.+0.j 1.-0.j 0.+0.j -5.-0.j] [ 5.+0.j 0.+0.j 3.+0.j 5.-0.j 0.+0.j 1.-0.j] [ 0.+0.j 1.+0.j 5.+0.j 3.+0.j 0.+0.j 0.+0.j] [ 1.+0.j 0.+0.j 0.+0.j 0.+0.j -3.+0.j -5.-0.j] [ 0.+0.j -5.+0.j 1.+0.j 0.+0.j -5.+0.j -3.+0.j]] Is there a way to know how is the basis ordered?

2 1

Kwant Installation issues (Mac)
by Girish Sharma Feb. 13, 2015

Feb. 13, 2015

Hi, I am trying to install Kwant on my mac. I have Macports installed. I ran the following command as described: echo http://downloads.kwant-project.org/macports/ports.tar |\ sudo tee -a /opt/local/etc/macports/sources.conf >/dev/null After running -sudo port selfupdate, I get the following error message: ---> Updating MacPorts base sources using rsync MacPorts base version 2.3.0 installed, MacPorts base version 2.3.3 downloaded. ---> Updating the ports tree Error: Extractinghttp://downloads.kwant-project.org/macports/ports.tar failed (can't read "verboseflag": no such variable) Error: Extracting http://downloads.kwant-project.org/macports/ports.tar failed (can't read "verboseflag": no such variable) Error: Extracting http://downloads.kwant-project.org/macports/ports.tar failed (can't read "verboseflag": no such variable) Error: Extracting http://downloads.kwant-project.org/macports/ports.tar failed (can't read "verboseflag": no such variable) Error: Extracting http://downloads.kwant-project.org/macports/ports.tar failed (can't read "verboseflag": no such variable) Error: Extracting http://downloads.kwant-project.org/macports/ports.tar failed (can't read "verboseflag": no such variable) Error: Extracting http://downloads.kwant-project.org/macports/ports.tar failed (can't read "verboseflag": no such variable) Error: Couldn't sync the ports tree: Synchronization of 7 source(s) failed Please run `port -v selfupdate' for details. Error: /opt/local/bin/port: port selfupdate failed: Couldn't sync the ports tree: Synchronization of 7 source(s) failed Could you please help me with it. Thank you for your time, and I greatly appreciate your help. Best regards, Girish

2 1