Mailman 3 July 2014 - 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))

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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

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leads with different lattice ?
by Yuanxi Wang July 24, 2014

July 24, 2014

Dear all, I'd like to know if it is possible to construct/attach leads with lattices different from the main scattering region, or even leads with custom geometry unrelated to the scattering region? For example if my scattering region is an amorphous cluster whose geometry have defined by hand, and I want to build leads using their own lattice to the left and right. Is that allowed in KWANT? (Of course in that case one would need define bonds/hoppings between and within the leads, and also from the lead to the main scattering region... but how..) Thanks Yuanxi -- Yuanxi Wang, Pennsylvania State University Department of Physics 104 Davey Lab #117, University Park, PA 16802

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Re: [Kwant] leads with different lattice ?
by Yuanxi Wang July 22, 2014

July 22, 2014

Dear Michael, Thanks for your prompt response. That is exactly what I am now trying to achieve: make the lead by repeating only a portion of the scattering region, using the shape function to crop out the portion that I want; meanwhile the amorphous scattering region is defined within a single huge "lattice" with only one cell, containing the entire scattering region. But the periodicity of the lead would be much smaller than the size of the scattering region, and I would get the error that the lattice vectors of the scattering region is not commensurate with the periodicity (TranslationalSymmetry) of the leads. Am I missing something here? Thanks Yuanxi 2014-07-22 2:36 GMT-04:00 Michael Wimmer <wimmer(a)lorentz.leidenuniv.nl>: > Dear Yuanxi, > > the way that attaching the leads works in kwant requires that the > scattering region contains the same lattice as the leads. However, you can > still easily achieve what you want: You only have to add a thin slice of > lead lattice to the scattering region, this will also allow you to define > all the irregular hoppings from the lead lattice to the scattering region. > Then you can use attach_lead to add the lead to the system. > > Adding a thin slice of lead lattice to the scattering region only creates > a negligible computational overhead, and gives the same physical result (as > what is "scattering region" and what is "lead" is mostly a matter of > definition). > > Best, > > Michael > > Am 22 jul. 2014 um 07:35 schrieb Yuanxi Wang <yuanxi.wang(a)gmail.com>: > > Dear all, > > I'd like to know if it is possible to construct/attach leads with > lattices different from the main scattering region, or even leads with > custom geometry unrelated to the scattering region? > > For example if my scattering region is an amorphous cluster whose geometry > have defined by hand, and I want to build leads using their own lattice to > the left and right. Is that allowed in KWANT? > > (Of course in that case one would need define bonds/hoppings between and > within the leads, and also from the lead to the main scattering region... > but how..) > > Thanks > Yuanxi > > -- > Yuanxi Wang, > Pennsylvania State University > Department of Physics > 104 Davey Lab #117, > University Park, PA 16802 > > -- Yuanxi Wang, Pennsylvania State University Department of Physics 104 Davey Lab #117, University Park, PA 16802

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SNS structure with KWANT
by Md.Iftekher Chowdhury July 21, 2014

July 21, 2014

Dear Authors, My name is Iftekher Chowdhury. I'm currently trying to understand KWANT better and I find it really amazing. I am trying to model Superconductor-Normal-Superconductor (SNS) with KWANT following the Superconductor-Normal script provided in the documentation. I have made several attempts but I failed to produce two symmetric differential conductance peak around the two barriers in the scattering region. I am sure I do not understand properly few of the key concepts addressed in KWANT. I have attached the trial scripts herewith. I would be reallt grateful if you could kindly advice and guide me on my error in understanding and how to produce two differential conducting peak in the SNS structure. Kind Regards Iftekher NOTE: Please cc me kindly for any response in order for me to receive the followup via email.

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Paper, screencast, bugfix release 1.0.1
by christoph.groth＠cea.fr July 4, 2014

July 4, 2014

Dear users of Kwant, We are pleased to announce the publication of the Kwant paper as New J. Phys. 16, 063065 (2014). In the published version we put Kwant in a broader context, motivate its design more clearly, and provide a real-world-research usage example. http://downloads.kwant-project.org/doc/kwant-paper.pdf We have also prepared a short video that demonstrates the use of Kwant directly. We invite you to relay the following link to anyone who may be interested: http://kwant-project.org/doc/kwant-screencast-2014 On a final note, Kwant 1.0.1 has been released. This is a maintenance release that fixes several minor bugs in Kwant 1.0.0. If you are not experiencing any technical problems with Kwant, you may choose to simply skip this upgrade. A list of all the changes in 1.0.1 is available at http://git.kwant-project.org/kwant/log/?h=v1.0.1 On Linux systems where Kwant has been installed in the standard way (apt-get), the upgrade to 1.0.1 should be performed as a part of a regular system upgrade. Windows and Mac users who want to upgrade need to re-install Kwant. See below for Mac upgrade instructions. Best wishes on behalf of all Kwant authors, Christoph Groth ---------------------------------------------- To upgrade kwant in macports, do sudo port upgrade py27-kwant (or py26-kwant, depending on whether you are using python 2.6 or 2.7). Follow the instructions for additional commands you have to execute. To upgrade Mac homebrew, some extra steps are needed because of some recent internal changes in homebrew. To upgrade kwant safely, do brew uninstall scipy numpy matplotlib kwant brew uninstall mumps_seq metis4 scotch5 gfortran brew update brew install gcc pip install python-dateutil brew install numpy scipy matplotlib brew install kwant For future updates of kwant, a simple "brew upgrade kwant" should be sufficient.

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Incoherent transport
by Ted Pudlik July 1, 2014

July 1, 2014

Hello, Is it possible to use kwant to simulate incoherent transport processes (photon and phonon scattering) and compute quantities such as the optical conductivity? Has anyone ever done it? Best wishes, Ted Pudlik Boston University

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