Dear all,
There is some code dealing with Majorana fermions: "A.7 Majorana Fermion"
on the paper "Kwant: a software package for quantum transport", by Christoph
et al.
I am still a novice and I'm not familiar with the physical system the code
is written for. Neither do I understand why the onsite and hopping matrices
are both 4*4 instead of 2*2 or something.
May I know if there is some paper describing the model for this code, and
why the onsite and hopping matrices are both 4*4?
Thanks and regards,
Tony

Dear Anton,
thank you very much for your reply. To be more specific, my problem is
the following :
in the example closed_system.py, if I put the B dependance in the
make_system function as
make_system(a=1, t=1.0, r=10, B=0.):
and simply put the
expression of the B-dependant hopping terms instead of using the hopx
subfunction, then I will obtain a spectrum which is B-independent.
Best,
Anil
Le Lun 20 janvier 2014 11:50, Anton Akhmerov a écrit :
> Dear Anli,
>
>
> In Kwant there are two ways to alter the values of matrix
elements
of
> the Hamiltonian after the system have been finalized. The first
one,
and
> also the preferred one is to use the 'args' argument
to the
value
> functions. The other option is to use the fact that the functions
can
> access e.g. global variables. However both methods have exactly
the
same
> scope, and there is hence no reason to not use the
'args'
argument.
>
> Can you be more specific with what you mean by "This seems
not
to
> always work", perhaps the problem is with the way you used
the
extra
> parameter for the functions?
>
> Best,
> Anton
>
>
> On Sun, Jan 19, 2014 at 11:38 PM, Anil Murani
<anil.murani(a)u-psud.fr>
> wrote:
>
>> Dear all,
>>
>>
>> I am facing a problem when it comes to parametrize a system
in
Kwant :
>> I am
>> using the same "trick" as in the example on closed
system
>> (closed_system.py)
>> where the parameter B is defined in a subfunction of
make_system. This
>> seems not to always work ; do you have a better alternative
which avoids
>> to finalize the system with different magnetic fields ?
>>
>> Regards,
>>
>>
>> Anil
>>
>

Dear all,
First off, thanks for all the hard work in this. Very much appreciated!
I'm trying to write a system with a p-wave scattering region ( H =
(p^2+V-\mu)\sigma_z +1/2 {\alpha, p} \cdot \sigma) with normal metal leads
(\alpha = 0 in the leads). For simplicity, I'm going to talk about 1-D
systems (chains) here, although I'm working on 2D systems.
Because of the term linear in p, you can't take it directly to zero. For
example: Define the p-wave parameter to be zero in the hopping between
sites x=0 and x=1 (with lattice spacing=1). Then define the hopping between
sites x=1 and x=2 to to be =1. Then, this will force all of the hoppings to
undulate between 0 and 1. The way around this is to define it to be zero in
one hopping, then 0.5 in the next hopping, and then 1 in the hopping after
that.
My question is: Is this automatically implemented?
(Just in case, I'm putting this in by hand, not using HoppingKind, but
iterating over nearest neighbors and conditionally setting sys[lat(x,y),
lat(x+1,y) ] to values I want. )
Thank you very much,
Baris

Dear all,
I am facing a problem when it comes to parametrize a system in Kwant : I
am using the same "trick" as in the example on closed system
(closed_system.py) where the parameter B is defined in a subfunction of
make_system. This seems not to always work ; do you have a better
alternative which avoids to finalize the system with different magnetic
fields ?
Regards,
Anil