2023-10-18 マサチューセッツ工科大学(MIT)
◆この発見は、超低電力で高容量のデータストレージデバイスを設計するのに役立つ可能性があり、クラシカルおよび量子コンピュータ向けの革新的な技術を可能にするかもしれません。グラフェンは非常に薄いが非常に強力で、特定の配置で積み重ねると、予想外の電子挙動を示すことがあります。この発見は、グラフェンの潜在的な利用価値をさらに拡大する可能性があるとされています。
＜関連情報＞
- https://news.mit.edu/2023/five-layer-graphene-sandwich-rare-electronic-behavior-1018
- https://www.nature.com/articles/s41586-023-06572-w
五層菱面体グラフェンにおける軌道の強誘電性 Orbital multiferroicity in pentalayer rhombohedral graphene
Tonghang Han,Zhengguang Lu,Giovanni Scuri,Jiho Sung,Jue Wang,Tianyi Han,Kenji Watanabe,Takashi Taniguchi,Liang Fu,Hongkun Park & Long Ju
Nature Published:18 October 2023
DOI:https://doi.org/10.1038/s41586-023-06572-w
Abstract
Ferroic orders describe spontaneous polarization of spin, charge and lattice degrees of freedom in materials. Materials exhibiting multiple ferroic orders, known as multiferroics, have important parts in multifunctional electrical and magnetic device applications1,2,3,4. Two-dimensional materials with honeycomb lattices offer opportunities to engineer unconventional multiferroicity, in which the ferroic orders are driven purely by the orbital degrees of freedom and not by electron spin. These include ferro-valleytricity corresponding to the electron valley5 and ferro-orbital-magnetism6 supported by quantum geometric effects. These orbital multiferroics could offer strong valley–magnetic couplings and large responses to external fields—enabling device applications such as multiple-state memory elements and electric control of the valley and magnetic states. Here we report orbital multiferroicity in pentalayer rhombohedral graphene using low-temperature magneto-transport measurements. We observed anomalous Hall signals Rxy with an exceptionally large Hall angle (tanΘH > 0.6) and orbital magnetic hysteresis at hole doping. There are four such states with different valley polarizations and orbital magnetizations, forming a valley–magnetic quartet. By sweeping the gate electric field E, we observed a butterfly-shaped hysteresis of Rxy connecting the quartet. This hysteresis indicates a ferro-valleytronic order that couples to the composite field E · B (where B is the magnetic field), but not to the individual fields. Tuning E would switch each ferroic order independently and achieve non-volatile switching of them together. Our observations demonstrate a previously unknown type of multiferroics and point to electrically tunable ultralow-power valleytronic and magnetic devices.
