2022-04-11 ペンシルベニア州立大学（PennState）
・原子レベルで薄く積層された層からなる2次元材料、マンガンビスマステルライドは、トポロジカル絶縁体の一例で、絶縁体であると同時に電気を通すことができるエキゾチックな材料だと、科学者達は言っています。
・この物質が磁性体でもあるため、その端に流れる電流はロスレス、つまり熱としてエネルギーを失わない可能性があるということだ。この材料の層間の弱い磁気結合を調整する方法を見つけることで、このような機能を発揮させることができるかもしれない。
・科学者たちは、材料中の原子の微小な振動（フォノン）が、この機能を実現する方法のひとつになるかもしれないと、『Nature Communications』誌に4月8日付けで発表した。
＜関連情報＞
- https://www.psu.edu/news/research/story/scientists-find-knob-control-magnetic-behavior-quantum-material/
- https://www.nature.com/articles/s41467-022-29545-5
MnBi2Te4における層間磁気音響結合 Interlayer magnetophononic coupling in MnBi2Te4
Hari Padmanabhan,Maxwell Poore,Peter K. Kim,Nathan Z. Koocher,Vladimir A. Stoica,Danilo Puggioni,Huaiyu (Hugo) Wang,Xiaozhe Shen,Alexander H. Reid,Mingqiang Gu,Maxwell Wetherington,Seng Huat Lee,Richard D. Schaller,Zhiqiang Mao,Aaron M. Lindenberg,Xijie Wang,James M. Rondinelli,Richard D. Averitt &Venkatraman Gopalan
Nature Communications Published: 08 April 2022
図1: MnBi2Te4の磁気相転移に伴うフォノン異常。
Abstract
The emergence of magnetism in quantum materials creates a platform to realize spin-based applications in spintronics, magnetic memory, and quantum information science. A key to unlocking new functionalities in these materials is the discovery of tunable coupling between spins and other microscopic degrees of freedom. We present evidence for interlayer magnetophononic coupling in the layered magnetic topological insulator MnBi2Te4. Employing magneto-Raman spectroscopy, we observe anomalies in phonon scattering intensities across magnetic field-driven phase transitions, despite the absence of discernible static structural changes. This behavior is a consequence of a magnetophononic wave-mixing process that allows for the excitation of zone-boundary phonons that are otherwise ‘forbidden’ by momentum conservation. Our microscopic model based on density functional theory calculations reveals that this phenomenon can be attributed to phonons modulating the interlayer exchange coupling. Moreover, signatures of magnetophononic coupling are also observed in the time domain through the ultrafast excitation and detection of coherent phonons across magnetic transitions. In light of the intimate connection between magnetism and topology in MnBi2Te4, the magnetophononic coupling represents an important step towards coherent on-demand manipulation of magnetic topological phases.
