Hi,
Recently, I used ATK 2017 to calculate the I-V curve in a molecular magnetic tunneling junction (MTJ) at its antiparallel (AP) spin configuration (i.e. the spins on two electrodes are opposite). I found a very strange phenomenon. i.e. the I-V curve is not symmetrical at high negative and positive bias voltages (+-0.5 V). Please note that the geometric structure of MTJ is symmetrical (i.e., there is a mirror symmetry pendicular to z axis, only the spins on two electrodes are opposite ).
Then, I carefully read some references, and found that this phenomenon is not unique. For example, see DOI: 10.1039/c4ra09279a (Figure 3b), or DOI: 10.7498/aps.66.198503 (Figure 2b). Please note that although the second example is not written in English, it is not hard to understand the meaning of the figure. In the two examples, the geometric structures is symmetrical (this can also be verified from the LDOS, various eigenstates etc.) , but at high bias voltage, the spin current is asymmetrical.
At AP configuration, if the device is symmetrical (have mirror symmetry), one spin in one electrode should be identical to another spin in another electrode. According to symmetry, at +-Vb, the spin currents should be 'identical', except a sign indicating the direction. This should be indenpent on the details of the device. So, is there anything wrong in the calculation?
Thank you in advance.
