The meaning of the current in Z direction

[bubble]

Hi,
   In the IV-Plot (see the 1.jpg in the attachment), one choice of the spin is "Z". Its meaning is unclear for me , and I have two questions. 
   1. What is the physical meaning of the choice Z? Is it about non-collinear (or non-collinear with spin orbit coupling) calculation?
   2. In common spin-polarized (collinear) calculation, the 'Z' result is different from that of the 'sum, up or down'. I wonder why the difference occurs.
Thank you.

[Anders Blom]

See http://www.quantumwise.com/documents/manuals/latest/ReferenceManual/index.html/ref.spin.html
Z = spin.up - spin.down

However, your I-V curve must have some mistake. It is impossible for the current to change sign for the same sign of the bias.

[narin]

Hi Mr. Blom,

There is also a similar problem with my IV curve of the doped GNR simulation. http://quantumwise.com/forum/index.php?topic=3682.0

The IV curve seems the opposite direction, so I guess current flows in z- direction when the applied voltage is positive. Is there a way to correct it in ATK?

Thanks.

[Anders Blom]

I don't think so, there you have no change of sign for the same of bias.