Hi Joe,
Thanks for your fast response. I think I might not have been clear with what I am attempting, so I included a diagram as an attachment.
I'm trying to study a system where a contact has been patterned around the outer edge of a channel. Initially I have tried attaching one lead oriented along the z-direction (similar to the Hanle valve example in the Kwant paper), which allows me to make one lead which boarders two sides of the device (and vertical leads in the middle).
Unfortunately, these do not seem to work in the way that I want. Even with a very large number of modes in such a lead, it seems that only a few modes actually are able to transmit into the channel. I suspect this has to do with the primarily z-transporting waves having to somehow convert into transporting only in the plane of the channel- most just reflect back into the lead.
Instead, I have been trying to solve the problem using a solution where the leads are constructed in the plane of the sample. One approach I have taken to this is separating the lead into two, one along x and one along y (labeled virtual contact 1 and 2). Since these two contacts are treated independently, they are out of phase with one another.
My hope is to somehow construct one contact (with 1 translational symmetry) that has a width of the perimeter of the red line in my diagram. I would like to then attach the contact in such a way that it bends around the corner. It sounds like this would not be possible though.
A side question then- Is there anyway that you know of that I could tell Kwant to treat the virtual contacts I labeled in my diagram such that the waves would be coherent with one another? Currently the big problem that I face with that method is the waves coming out of the contacts do not interfere.
Thanks!
Sam
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From: Joseph Weston
I am working on trying to create a system where there is a lead which wraps around the edge of a sample.
For example, I have included a code which generates a square scattering region with two contacts, one extending vertically and the other extending horizontally. What I would like to do is combine these two contacts into a single contact, so this might represent a system where there is a contact that has been etched surrounding a central region.
I think that the way to approach this would be to generate one wide contact, whose width is equal to the combined with of the contacts in my code (40 in my example). This contact would then be attached to the channel and its interface would be wrapped around the channel. Unfortunately, I am at a bit of a loss as to how I would code this.
My main reason for wanting to do this rather than treat the problem with two separate leads is that the modes are going to be different between the two. Ultimately, it would be nice to be able to do this in a way that wraps the lead completely around the outer edge of the channel to simulate some sort of open boundary condition. Additionally, it would be nice to do something similar with a hole in the middle of the scattering region, to construct a Corbino disk.
If I understand correctly, you would like to construct a lead with a 2D translational symmetry and solve a scattering problem where you attach this lead to some 0D scattering region. Unfortunately this is not something that Kwant is capable of, currently. Essentially the fact that you have a 2D lead means that you will have an infinite number of modes at a given energy (waves can be scattered at arbitrary angles). This is in constrast to the case with (quasi-) 1D leads where there are a finite number of modes at a given energy. This is definitely a direction where we are looking to extend Kwant, however it will be some time before we have anything concrete.
