Nuclear spin polarization by out-of-plane spin injection from ferromagnet into an InAs heterostructure
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Nuclear spin polarization by out-of-plane spin injection from ferromagnet into an InAs heterostructure Tomotsugu Ishikura, Takahiro Hiraki, Takashi Matsuda, Joungeob Lee and Kanji Yoh Research Center of Integrated Quantum Electronics, Hokkaido University, Sapporo, Japan
Abstract We have investigated an InAs channel Hall-bar structure with ferromagnetic spin injector in one of the current terminals. After magnetizing the Fe electrode, spin polarized electrons are injected through the edge of the isolation mesa structure and the anomalous Hall voltage is observed, when electrons are injected from the ferromagnetic terminal. However, when electrons are injected from the non-magnetic metal (Ti/Au) of opposite terminal, the Hall voltage disappeared to the variation error level due to the fabrication imperfections. This result suggests the possibility that out-of-plane spin injection from the channel edge lead to perpendicular nuclear magnetic field. It is presumably caused by nuclear spin polarization in InAs channel near the spin source edge through Overhauser effect. The estimated internal magnetic field was 2000 Gauss.
Introduction Interaction of electron and nuclear spin in semiconductors has gained great potential for several applications in spintronics, which spin degree of freedom is applied to electronic devices. [1-2] So far a number of spin injection and detection to semiconductors have been tried by ferromagnetic metal or circular polarized light in various methods, such as spin accumulation non-local geometry, spin light emitting diode and so on [3-6]. Narrow-gap semiconductors have high spin orbit coupling and deserved for Datta-Das type spin transistor applications. In a special condition when the two types of spin-orbit interaction (Rashba and Dresselhaus effect) are met, so called Persistent Spin Helix (PSH) condition allows all electron spins undergo precession synchronously [7-11]. On the other hand, PSH condition is supposed to be failed, spin relaxation of narrow-gap semiconductors are strong to cause spin relaxation with D’yakonov Perel mechanism and the resulting in spin diffusion length of less than 1µm. [7-12] On the other hand, if the two types of spin-orbit interaction are nearly matched, spin diffusion length extends up to few micrometer to 10 µm. When the injected spin polarization are maintained stationary, the dynamic nuclear polarization (DNP) based on hyperfine interaction [13] lead to transfer from electron to nuclear spin angular momentum dynamically near the injection edge. If the electron spin is transferred to nuclear spins, effective magnetic field is induced without applying external magnetic field. So far, a number of experiments for application in spintronics have been demonstrated the control of nuclear spin in semiconductors, which have become realistic by various methods such as quantum Hall state edge current [14], creation of spin polarized electrons in quantum dots by irradiating circularly polarized light [15] and nuclear magnetic resonance [16-18], nuclear spin polarizat
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