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Detection of spin polarization with a side coupled quantum dot

Introduction

Electrons have freedom in not only the charge but also the spin. Utilizing the spin, it will be possible to create new devices.

But conventional electronic measurements have no sensitivity on the spin. We demonstrate a new method to probe spin polarization in solids.


Experiment

The right figure shows the schematic of the device. A quantum dot is coupled to the target of the measurement.

Some states in the quantum dot have spin selectivity. By measuring the electron injection into the states, we can get the information of the spin polarization in the target.

The right graphs show the schematics of the measurement utilizing Zeeman split apin states. The difference in the spin polarization makes the difference in the electron injection and the measured signal.










The right figure shows the measured signal when we used the quantum wire in the magnetic field, which has spin polarized channels as a controllable spin polarized source.

The signal structure changes from two to single-step with the change of the spin polarization in the wire.














The right graph shows the measured result when we changed the wire condition in more detail.

The red points near 0.5 and 1 correspond to no spin polarization and spin polarization, respectively.

This behavior is consistent with the expected result from the measured conductance of the wire. This certifies the operation of the spin polarization detection.











Similar polarization detection will be available even in the zero magnetic field utilizing the spin-singlet and triplet states in the quantum dot.

The right figure shows the procedure to control the states in the dot for the detection.



Conclusion

We demonstrated detection of spin polarization by measuring the electron injection into the spin dependent states in a quantum dot.

We also proposed a method to detect spin polarization even in the zero magnetic field.


Reference

"Detection of spin polarization with a side-coupled quantum dot", T. Otsuka, E. Abe, Y. Iye, and S. Katsumoto, Physical Review B 79, 195313 (2009).