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Introduction
Electrons have freedom in not only charge but also spin. By utilizing electron spins, it will be possible to create new devices.
To examine spin states (especially spin polarization) in solid devices microscopically, we have developed a method utilizing a semiconductor quantum dot. In this experiment, we have developed the method to be applicable in low magnetic fields and demonstrated the operation.
Experiment
The right figures show the schematics of our device. A quantum dot is coupled to a target device.
Some states in the quantum dot have spin selectivity. Especially the singlet and the triplet states show the selectivity even at the zero magnetic field and we can detect spin polarization in low magnetic fields utilizing the states.
We have checked the operation of this detection method using quantum Hall edge states, which create spin polarization in relatively low magnetic fields, as the target.
The right figures show the results of the measurement.
The left (right) one shows the result in spin unpolarized (polarized) case. In the unpolarized case, we can detect the electron tunneling into both the singlet and the triplet states. In the polarized case, electron tunnels mainly into the triplet states.
From this difference, we can extract the value of spin polarization.
The right figures show the extracted spin polarization.
The left (right) one shows the result with our new microscopic method (the conventional macroscopic method). With the increase of the magnetic field, spin polarization is formed.
With our detection method, we can detect spin polarization in relatively low magnetic fields. This corresponds to the local spin polarization formed at the device edge, which cannot be detected with the macroscopic methods, and demonstrates the effectiveness of our detection method to probe local spin polarization.
Conclusion
We have developed the method of spin polarization detection to be applicable in low magnetic fields. We confirmed the operation of the detection scheme using the quantum Hall edge states.
This new method will be useful in exploring interesting spin phenomena in low magnetic fields.
Reference
"Detection of spin polarization utilizing singlet and triplet states in a single-lead quantum dot", Tomohiro Otsuka, Yuuki Sugihara, Jun Yoneda, Shingo Katsumoto, and Seigo Tarucha, Phys. Rev. B 86, 081308(R) (2012).
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