Dynamic nuclear spin polarization in quantum point contact

2018.03.30.

Ibaraki Univ. Tomosuke Aono

Electron spins can be easily polarized using external magnetic fields, but it is not the case for nuclear spins. To achieve the nuclear spin polarization, there is a way that is known as the dynamic nuclear spin polarization (DNP); The polarization is achieved using spin flip-flop processes between electron spins and nuclear spins. In recent years, the NMR signals are detected by electric resistance changes through the system, which is known as the resistively-detected NMR, and the detection of the DNP formation in semiconductor nanostructures has been observed.

In this study, we theoretically investigate the DNP generation using a quantum point contact (QPC) and the resistively-detected NMR for the DNP. We consider the QPC system with in-plane magnetic fields. When the QPC is tuned to be spin selective, at the conductance of e2/h , a finite bias voltage induces a dipole-like (spatially anti-symmetric) nuclear polarization, the DNP of equal magnitude and opposite sign on the opposite leads as shown in the figure. It was found that this dipole-like DNP has qualitatively different response characteristics from that for the uniform nuclear spin polarization when it is detected by the resistively-detected NMR method.