Mailman 3 October 2022 - Kwant-discuss

To to separate spins, electron and hole
by Khani Hosein Oct. 11, 2024

Oct. 11, 2024

Dear all, I am using Kwant to study a system with both spins and electron and hole, so the hopping matrix is 4X4. Now I want to know how to separate the spins, electron and hole. I study this through the "2.6. Superconductors: orbital degrees of freedom, conservation laws and symmetries" smatrix = kwant.smatrix(syst, energy) data.append(smatrix.submatrix((0, 0), (0, 0)).shape[0] -smatrix.transmission((0, 0), (0, 0)) +smatrix.transmission((0, 1), (0, 0))) I do not find more information about this for kwant. For my system, if I have 3 leads, and the hopping and onsite energy is set in this order: (e↑,0,0,0)- spin up electron,first row of the 4X4matrix (0,e↓,0,0)- spin down electron,second row of the 4X4matrix (0,0, h↑ ,0)- spin up hole,third row of the 4X4matrix (0,0, 0, h ↓ )- spin down hole,fourth row of the 4X4matrix I want to obtain the transmissions from 0 →2. smatrix = kwant.smatrix(syst, energy) The transmission from h↑ to e↑ is: smatrix.transmission((2, 1), (0, 2)) The transmission from h ↓ to e↑ is: smatrix.transmission((2, 1), (0, 3)) Is my understanding correct? Thanks very much in advance! Hosein Khani

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Realistic values of hopping parameters
by Yu Li Oct. 19, 2023

Oct. 19, 2023

Dear all, Now I’m studying some transport property based on multilayered system, with nonmagnetic layer/ferromagnetic layer (NM/FM) stack. May I ask when creating a tight binding system, and setting hoppings by the following function: syst[(lat(1, 0), lat(1, 1))] = t, how to associate the hopping with a realistic system? Such as hoppings between FM and FM atoms, or between FM and NM atoms? I found in many literatures people just simply put t=1, but I assume the value should depend on the type of atoms. My another question is, is it possible to define more than one type of hopping between two sites? For the tight-binding approximation of p electrons, there are two types of hopping integrals: Vppσ, and Vppπ, so I’m wondering if it’s possible to simulate the effect of both hoppings? Thanks a lot for reading my questions! Cheers, Yu Li

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Defining uniaxial strain in specified region of graphene
by shrushti.tapar07＠gmail.com Jan. 20, 2023

Jan. 20, 2023

I want to create the graphene strained superlattice-like structure, having uniaxial strain defined at the specified region. Please, someone can suggest to me how to define the strained region and interface between unstrained and strained graphene regions. Thanks in Advance Shrushti

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Attaching lead to a system
by Shashank Kumar Nov. 3, 2022

Nov. 3, 2022

Hi all, I have made a one dimensional system with 3 sub-lattices. However, in order to attach leads I have to make a lead and manually attach it to sublattice A. But, apparently this code below is not working. Any suggestion will be help full. def make_system(nlattice): lat = kwant.lattice.Polyatomic([(1, 0), (0, 1)], [(0, 0), (1/3.0, 0), (2/3.0, 0)]) sub_a, sub_b, sub_c = lat.sublattices # central scattering region syst = kwant.Builder() syst[(sub_a(x,0) for x in range(nlattice))] = 4 syst[(sub_b(x,0) for x in range(nlattice))] = 4 syst[(sub_c(x,0) for x in range(nlattice))] = 4 syst[lat.neighbors()] = -1 # add leads lat_lead = kwant.lattice.square() sym_lead1 = kwant.TranslationalSymmetry((-1, 0)) lead1 = kwant.Builder(sym_lead1) lead1[lat_lead(-1, 0)] = 4 lead1[lat_lead.neighbors()] = -1 syst[lat_lead(-1,0)] = 4 syst[lat_lead(-1,0), sub_a(0,0)] = -1 syst.attach_lead(lead1) syst.attach_lead(lead1.reversed()) kwant.plot(lead1) return syst fsyst = make_system(nlattice=10).finalized() kwant.plot(sys, fig_size=[10,8], site_size=0.2) Shashank Kumar

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Problem in Bandstructure of AGNR defect
by sahu.ajit92＠gmail.com Oct. 15, 2022

Oct. 15, 2022

Dear all, I make AGNR in Kwant and introduce the defect in both the scattering region and lead. When plotting the bandstructure of the lead there is a straight line that comes at E=0. I am confused that there is some error in the code or not. Please help Thanking You code- ________________ import kwant import numpy as np import matplotlib.pyplot as plt pi = np.pi a = 1 d = 1.42; a1 = d*np.sqrt(3); lat = kwant.lattice.general( [[a1, 0], [a1/2, a1*np.sqrt(3)/2]],[[0, 0], [0, a1/np.sqrt(3)]] ) a,b = lat.sublattices def set_pub(): # for plotting the figures plt.rcParams.update({ "font.weight": "bold", # bold fonts "font.size":18, #"tick.labelsize": 15, # large tick labels "lines.linewidth": 2, # thick lines "lines.color": "k", # black lines "grid.color": "0.5", # gray gridlines "grid.linestyle": "-", # solid gridlines "grid.linewidth": 0.5, # thin gridlines "xtick.major.size":10, "xtick.minor.size":5, "ytick.major.size":10, "ytick.minor.size":5, "savefig.dpi": 600, # higher resolution output. }) def make_sys(w,l): def rect(pos): x,y = pos return -w*a1<x<w*a1 and -l*a1<y<l*a1 model1 = kwant.Builder() model1[lat.shape(rect,(1,1))] = 0 model1[lat.neighbors()] = 2.46 return model1 def lead_join(model1,w): def lead_shape(pos): x, y = pos return -w*a1<x<w*a1 Num = 8*(a1*np.sqrt(3)/2) sym = kwant.TranslationalSymmetry([0,Num]) lead = kwant.Builder(sym) lead[lat.shape(lead_shape, (1,1))] = 0 lead[lat.neighbors()] = 2.46 model1.attach_lead(lead) model1.attach_lead(lead.reversed()) return model1,lead def defect(model1,lead): def delet_lead(pos, shift = +a1*np.sqrt(3)): x, y = pos z=x**2+(y-shift)**2 return z<(a1)**2 def delet_str(pos, shift = a1*np.sqrt(3)): x, y = pos z = x**2 + (y-shift)**2 return z<(a1)**2#z<(2*a1)**2 del model1[lat.shape(delet_str, (1,1))] del lead[lat.shape(delet_lead, (2,2))] kwant.plot(model1) set_pub() plt.rc('axes', linewidth = 2.0) plt.show() return model1 def plot_bandstructure(flead, momenta): bands = kwant.physics.Bands(flead) energies = [bands(k) for k in momenta] band_gap = 100 for k in momenta: for band in bands(k): if(band <0): #Lower than fermi band min_band=band else: max_band=band if(max_band-min_band<band_gap): band_gap=max_band-min_band break print("Gap Energy= " + str(band_gap) +" ev ") kwant.plotter.bands(flead) # bandstructure of lead plt.ylim([-3,3]) set_pub() plt.xlabel("K $(\AA^{-1})$",fontweight='bold') plt.ylabel("Energy (eV)",fontweight='bold') plt.show() return band_gap def main(): w = 5 l = 8 sys = make_sys(w,l) syst,lead = lead_join(sys,w) syst = defect(syst,lead) fsys = syst.finalized() momenta = [-pi + 0.02 * pi * i for i in range(101)] Band_Gap = plot_bandstructure(lead.finalized(), momenta) if __name__ == '__main__': main()

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Re: Problem in Bandstructure of AGNR defect
by Ajit Kumar Sahu Oct. 15, 2022

Oct. 15, 2022

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