2019 Fiscal Year Annual Research Report
酸化還元活性な配位高分子における磁気・電子相関の交差制御
| Project/Area Number |
18J20896
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| Research Institution | Tohoku University |
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Principal Investigator |
黄 柏融 東北大学, 理学研究科, 特別研究員(DC1)
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| Project Period (FY) |
2018-04-25 – 2021-03-31
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| Keywords | chirality / photogalvanic effect / lead iodides / Spin-orbit coupling |
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| Outline of Annual Research Achievements |
The introduction of chirality to the 2D organic-inorganic hybrid perovskite-type (OIHP) materials for novel physical properties and potential applications is the main target of this work in present. Previously,a opto-electronic phenomenon bulk photovoltaic effect, namely, the generation of zero-bias photocurrent in a chirality introduced 2D OIHP lead iodides has been successfully detected and the work was published last year. However, spin-orbit coupling (SOC) in this type of materials also provide bright route to optp-spintronic applications. Based on this, we have prepared another chirality introduced 2D OIHP lead iodides which is chiral but nonpolar. Due to the presence of both chirality and SOC from heavy atoms, spin-splitting of bands and the generation of zero-bias photocurrent is expected by using circular polarized light. The so-called circular photogalvanic effect (CPGE) is allowed in non-centrosymmetric systems with strong SOC and has been studied in the surface/bulk polar OIHP lead halides. However, the chiral system is still lack of discovery. By using the materials prepared, we successfully detected CPGE photocurrent and observed the chirality dependence based on the radial spin texture proposed for spin-momentum locking in chiral system. This result indicates that chemical designable OIHP lead halides is an excellent platform for pursuing not only electronic but also spintronic phenomena for promising applications.
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| Current Status of Research Progress |
Current Status of Research Progress
1: Research has progressed more than it was originally planned.
Reason
The process of pushing electronic phenomenon to spintronics is quite successful for the strategy of introducing chiral organic cations into 2D organic-inorganic hybrid perovskite-type (OIHP) materials. Normal zero-bias photocurrent has been detected using unpolarized white light radiation on non-centrosymmetric OIHP lead iodides, while the direction of such current reverses when the chirality is opposite. Circular photogalvanic effect (CPGE) was detected followed in a pair of chiral/nonpolar OIHP lead iodides. The incorporation of non-centrosymetry and spin-orbit coupling (SOC) in these semiconductors gives rise to spin-splitting of bands and the flow of spin-polarized photocurrent in the light covering direction under exposure of circular polarized light. The sign of photocurrent also reverses between opposite chirality of materials, reflecting the proposed radial spin texture of spin-momentum locking for chiral system with strong SOC. This work will be published soon in the future.
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| Strategy for Future Research Activity |
Since the circular photogalvanic effect (CPGE) based on chirality was observed successfully, we decided to detect CPGE in the bulk polarity origin which is also lack of observation compared with the ones with surface origin. A pair of chiral/polar organic-inorganic hybrid perovskite-type (OIHP) lead iodides was prepared for the CPGE experiments. Basic characterization of these materials have been accomplished and the CPGE photocurrent in the polar configuration will be measured soon.
Besides, copper ions were used to replace lead ions for the introduction of magnetism as a degree of freedom. The ferromagnetic behavior of 2D OIHP copper halides have been widely reported. In this system, chirality can be introduced as well for the achievement of Dzyloshinskii-Moriya interaction (DMI), which can further lead to anomalous magnetic behavior as well as specific spin texture like magnetic skyrmion. The DMI is originated from non-centrosymmetry and sizable spin-orbit coupling (SOC) in magnetic coupled system, so that the targeted magnetic behavior can be rationally designed in OIHP materials. We have prepared several compounds and anomalous magnetic behavior at low temperature was discovered. Neutron diffraction measurements on deuterated single crystal samples were scheduled for the details of wave number representing spin wave period.
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