Mailman 3 July 2020 - Kwant-discuss

(no subject)
by Prof. CHAN Kwok Sum July 29, 2020

July 29, 2020

Dear Kwant developer, I want to define a spatially varying current operator which depends on the two sites of a bond. Can this be done giving the “onsite” a function in the current operator definition. According to the manual, the function for onsite has the signature of a Hamiltonian on-site function, does it mean the function can only have one site as its input and cannot have two sites of a bond as input? If “onsite” cannot do the job, any suggestion of how to solve the problem? Regards, KS Chan Disclaimer: This email (including any attachments) is for the use of the intended recipient only and may contain confidential information and/or copyright material. If you are not the intended recipient, please notify the sender immediately and delete this email and all copies from your system. Any unauthorized use, disclosure, reproduction, copying, distribution, or other form of unauthorized dissemination of the contents is expressly prohibited.

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Changing color limits with kwant.plotter.plot
by Jannis July 20, 2020

July 20, 2020

Dear kwant community, Is there any way to change the color limits in kwant.plotter.plot? I use the site_color in kwant.plotter.plot to map my data on a 3D system. In contrast to kwant.plotter.map, there is no vmin/vmax option. I know that I can assign the figure to a subplot with ax. But I haven't found a way to create a colorbar or set the color limits with this option, because I lack a mappable. Has anyone figured out how to do this? (or if it is possible) Thanks, Jannis

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Phonon transmission in Kwant
by Ran Mutc July 12, 2020

July 12, 2020

Dear Kwant developers, I wonder whether it is possible to calculate phonon transmission via NEGF formalism in Kwant. For example within the force constant model, is it possible to construct the dynamical matrix and calculate phonon self energies via surface Green's functions? Or do you recommend any other way to implement the phonon transmission in Kwant? Best, Ran

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Re: Phonon transmission in Kwant
by Ousmane LY July 11, 2020

July 11, 2020

Hi Ran, the problem you described seems to be more adapted to tkwant or its extension tkwantOperator which computes energy and heat transport. So, you may give it a try. Regards, Ousmane

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Hamiltonian - Self energy matrix dimension mismatch
by mutc1r2595＠gmail.com July 7, 2020

July 7, 2020

Dear Kwant developers, I am trying to calculate the retarded Green's function for a simple 2D square lattice with two leads. Rather than using the following: G = kwant.greens_function(sys, energy) Gr10=G.submatrix(1,0) I need to calculate Green's function by Gr = (EI-H-Sigma_L-Sigma_R)^-1. But apparently I coudn't properly construct it in Kwant: Gr2=Np.linalg.inv(energy*Np.identity(W)-H-Sigma_Lr-Sigma_Rr) H = sys.hamiltonian_submatrix() The problem is dimensions of self energy matrices are WxW, where W is the width sites. However the Hamiltonian matrix I get above has the dimensions of NxN, where N is the number of sites in the scattering region. Do I use the wrong Hamiltonian? How should I implement Gr = (EI-H-Sigma_L-Sigma_R)^-1 correctly in Kwant? Thanks for your time, Ran

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Re: New version of KWANT
by Naveen Yadav July 6, 2020

July 6, 2020

Dear sir, Thank you for the information. My 3d system have both first and second nearest neighbour hopping z-direction if I have a perpendicular magnetic field in x-direction. By choosing landau gauge (0,0,By). It is easy to add peierls phase to first nearest neighbour hopping in z-direction. Now my question is how should I add the peierls phase for the second neighbour hopping in z-direction? Best Regards Naveen Yadav Research Scholar Department of Physics & Astrophysics University of Delhi New Delhi-110007 On Tue, Jun 30, 2020, 19:49 Anton Akhmerov <anton.akhmerov+kd(a)gmail.com> wrote: > Hi Naveen, > > That's mostly a convenience function. The same functionality, although > at a bit of a lower level is available in Kwant 1.4, see here: > > https://kwant-project.org/doc/1/pre/whatsnew/1.4#automatic-peierls-phase-ca… > > Best, > Anton > > On Sat, 27 Jun 2020 at 07:04, Naveen Yadav <naveengunwal72(a)gmail.com> > wrote: > > > > Dear sir, > > In the Kwant 1.5 documentation you have introduced > kwant.bulider.add_peierls_phase(syst). Is this functionality ready to use > by downloading the source code buider.py from gitlab? > > > > Best Regards > > Naveen Yadav > > Research Scholar > > Department of Physics & Astrophysics > > University of Delhi > > New Delhi-110007 > > > > On Fri, Jun 12, 2020, 15:42 Naveen Yadav <naveengunwal72(a)gmail.com> > wrote: > >> > >> Ok sir, thank you. > >> > >> Best Regards > >> Naveen Yadav > >> Research Scholar > >> Department of Physics & Astrophysics > >> University of Delhi > >> New Delhi-110007 > >> > >> On Fri, Jun 12, 2020, 14:25 Anton Akhmerov <anton.akhmerov+kd(a)gmail.com> > wrote: > >>> > >>> Dear Naveen, > >>> > >>> I fear you'll have to wait—it's not yet released. > >>> > >>> Best, > >>> Anton > >>> > >>> On Fri, 12 Jun 2020 at 10:51, Naveen Yadav <naveengunwal72(a)gmail.com> > wrote: > >>> > > >>> > Dear KWANT developers, > >>> > I am not able to update KWANT 1.5 > >>> > How can I update it? Please advise. > >>> > > >>> > > >>> > Best Regards > >>> > Naveen Yadav > >>> > Research Scholar > >>> > Department of Physics & Astrophysics > >>> > University of Delhi > >>> > New Delhi-110007 >

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Ground state wave function of Andreev bound states
by Chien-An Wang July 1, 2020

July 1, 2020

Dear Kwant community, (I don't know if here is a good place to ask this question. Let me know if it is inadequate. ) I calculate the eigen vectors of a close system containing a large s-wave superconductor and a small non-SC region. The spin is conserved, i.e. eigen states can be grouped into pure spin up and down. Can I infer the ground state wavefunction by the eigen vectors I obtained from kwant? The non-SC region is like a quantum dot. As calculated in [1], if there's a single orbital level and it couples to SC lead, the state in the quantum dot will become ground state |->=-v*|up,down>+u|0>, excited states |up> and |down>, and the highest excited state |+>=u|up,down>+v*|0>. However that is an effective model. I'm interested in how the ground state |-> looks like in tight binding model. Here is my procedure/reasoning: kwant can calculate BdG Hamiltonian on the lattice. The entire system has a ground state |g>, which is a product state of: |g> = (u1|psi1,up>|psi1,down> + v1|0>)*(u2|psi2,up>|psi2,down> + v2|0> )* ... . Here |0> is the state with no electron. The eigen vectors I obtained from kwant should be interpreted as excitations on |g>. Now I find a eigen vector localized in non-SC region. It is spin-up, with spin-up electron part [e1, e2, e3, ...] and hole part [h1, h2, h3, ...] at lattice points 1,2,3,... . These coefficients {e1,h1, e2,h2, e3, h3, ...} can be used to construct a fermionics operator gamma_up. Its Kramer's partner gamma_down would have spin-down part [e1, e2, e3, ...] and hole part [-h1, -h2, -h3, ...] at each lattice point. By applying gamma_up and gamma_down on |0> I can get one of the states in |g>. It turns out to be [sum_i {e_i h_i } + sum_i,j {e_i e_j a_i^dagger a_j^dagger}] |0>, where i,j are lattice point index, up to a normalization factor. Just as a reference, the onsite and hopping Hamiltonian are: def onsite(): (4 * p.t - p.mu + p.pot[x] ) * pauli.szs0 + p.delta[x]* pauli.sxs0 def hop(): -p.t * pauli.szs0 p.pot[x] is potential. p.delta[x] is pairing potential. pauli.szs0 is the tensor product of sigma_z (e-h basis) and identity (spin-basis). Thanks, Chien [1] "Self-consistent description of Andreev bound states in Josephson quantum dot devices", Phys. Rev. B 79, 224521 (2009)

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