Mailman 3 December 2021 - Kwant-discuss

Problems in calculating conductivity using the KPM method
by 674657065＠qq.com Jan. 7, 2022

Jan. 7, 2022

Dear all： I am a PHD student and i am using the kwant to calculate the conductivity of the graphene. Excuse me, I'd like to ask you a question that in the kwant documentation, you used the KPM method to calculate the conductivity of graphene. Does the disorder strength take a value of 0 or approach 0? If the disorder strength is 0, why is the conductivity not diverging at points where the energy is not zero? Thank you for your answer. Best wishes Hanlin Liu

2 1

Solving CIP - GMR in Kwant is tricky? doesn't work? or my code in wrong?
by chris stats Dec. 20, 2021

Dec. 20, 2021

Dear all, To test kwant as a beginner I wanted to solve a CIP GMR system (not CPP). Usual config. is 2 FMs separated by a NM; however because it is CIP, then the leads are partially connected to the 3 layers My system extends from the quantum wire problem adding Pauli matrices and the conservation law sigma_z I added impurities using a random function; however, my output sometimes shows a larger conductance for the antiparallel case (rather than the parallel one). No integration involved, simple conductance calculation using: "smatrix.transmission(1, 0))". From a code perspective, my only concern is on the leads, for instance I have for one ferromagnet: leftlead[(lat(0, j) for j in range(W))] = Jxc * (sigma_x*mx + sigma_y*my + sigma_z*mz ) I do not add impurities on the leads. the 4t term is not taken as i shifted the bandwidth. Is this a good "oversimplified approach? From a kwant perspective, As I said, sometimes the AP case is larger than the P config. Because of this I performed a random distribution average over 10000 loops and my result shows that in 25% of the cases AP is larger than P. Why it is not possible to get a solution to this system with low error? Is it because the quantum wire conductance problem is too simple to give proper results for CIP GMR? Shall I avoid using the conductance and focus instead on current out of equlibrium? Or CIP-GMR has particular constraints that I'm omitting in Kwant. Thanks a lot for a response...

1 0

New to Kwant. Basic bias voltage in quantum wire?
by statsconchris＠gmail.com Dec. 19, 2021

Dec. 19, 2021

Dear all, In the quantum wire set up I naively considered (oversimplfied) : left_lead[(lat(0, j) for j in range(W))] = (+0.5) right_lead[(lat(0, j) for j in range(W))] = (- 0.5) I wanted to have a bias voltage, muL > muR (0.5 eV in my case). I computed the conductance expecting to have different values for electrons flowing from left to right and right to left, i.e., smatrix.transmission(1, 0)) different from smatrix.transmission(0, 1)) but the results are identical! So my question is how do I actually construct a bias voltage and get the current from left to right different than from right to left. To oversimplify the problem I'm not interested in energy integration, let's assume that all the physics is dominated by electrons with a fixed energy value. Thank you for your answer

2 1