Crystal-liquid duality driven ultralow two-channel thermal conductivity in -MgAgSb

Li, J.*; Li, X.*; Zhang, Y.*; Zhu, J.*; Zhao, E.*; 古府 麻衣子; 中島 健次; Avdeev, M.*; Liu, P.-F.*; Sui, J.*; et al.

Applied Physics Reviews (Internet), 11(1), p.011406_1 - 011406_8, 2024/03

https://doi.org/10.1063/5.0173680

The desire for intrinsically low lattice thermal conductivity () in thermoelectrics motivates numerous efforts on understanding the microscopic mechanisms of heat transport in solids. Here, based on theoretical calculations, we demonstrate that -MgAgSb hosts low-energy localized phonon bands and avoided crossing of the rattler modes, which coincides with the inelastic neutron scattering result. Using the two-channel lattice dynamical approach, we find, besides the conventional contribution (70% at 300 K) from particlelike phonons propagating, the coherence contribution dominated by the wavelike tunneling of phonons accounts for 30% of total at 300 K. By considering dual contributions, our calculated room-temperature of 0.64 WmK well agrees with the experimental value of 0.63 WmK. More importantly, our computations give a nonstandard dependence, perfectly explaining the abnormal temperature-trend of in experiment for -MgAgSb. By molecular dynamics simulation, we reveal that the structure simultaneously has soft crystalline sublattices with the metavalent bonding and fluctuating liquid-like sublattices with thermally induced large amplitude vibrations. These diverse forms of chemical bonding arouse mixed part-crystal part-liquid state, scatter strongly heat-carrying phonons, and finally produce extremely low . The fundamental research from this study will accelerate the design of ultralow- materials for energy-conversion applications.

Extreme phonon anharmonicity underpins superionic diffusion and ultralow thermal conductivity in argyrodite AgSnSe

Ren, Q.*; Gupta, M. K.*; Jin, M.*; Ding, J.*; Wu, J.*; Chen, Z.*; Lin, S.*; Fabelo, O.*; Rodriguez-Velamazan, J. A.*; 古府 麻衣子; et al.

Nature Materials, 22, p.999 - 1006, 2023/05

https://doi.org/10.1038/s41563-023-01560-x

Ultralow thermal conductivity and fast ionic diffusion endow superionic materials with excellent performance both as thermoelectric converters and as solid-state electrolytes. Yet the correlation and interdependence between these two features remain unclear owing to a limited understanding of their complex atomic dynamics. Here we investigate ionic diffusion and lattice dynamics in argyrodite AgSnSe using synchrotron X-ray and neutron scattering techniques along with machine-learned molecular dynamics. We identify a critical interplay of the vibrational dynamics of mobile Ag and a host framework that controls the overdamping of low-energy Ag-dominated phonons into a quasi-elastic response, enabling superionicity. Concomitantly, the persistence of long-wavelength transverse acoustic phonons across the superionic transition challenges a proposed 'liquid-like thermal conduction' picture. Rather, a striking thermal broadening of low-energy phonons, starting even below 50 K, reveals extreme phonon anharmonicity and weak bonding as underlying features of the potential energy surface responsible for the ultralow thermal conductivity ( 0.5 WmK) and fast diffusion. Our results provide fundamental insights into the complex atomic dynamics in superionic materials for energy conversion and storage.

Two-dimensional quantum universality in the spin-1/2 triangular-lattice quantum antiferromagnet NaBaCo(PO)

Sheng, J.*; Wang, L.*; Candini, A.*; Jiang, W.*; Huang, L.*; Xi, B.*; Zhao, J.*; Ge, H.*; Zhao, N.*; Fu, Y.*; et al.

Proceedings of the National Academy of Sciences of the United States of America, 119(51), p.e2211193119_1 - e2211193119_9, 2022/12

https://doi.org/10.1073/pnas.2211193119

Although considerable progress has been made in the theoretical understanding of the low-dimensional frustrated quantum magnets, experimental realizations of a well-established scaling analysis are still scarce. This is particularly true for the two-dimensional antiferromagnetic triangular lattices. Owing to the small exchange strength, the newly discovered compound NaBaCo(PO) provides a rare opportunity for clarifying the quantum criticality in an ideal triangular lattice with quantum spin S=1/2. In addition to the establishment of the complete phase diagrams, the spin Hamiltonian with a negligible interplane interaction has been determined through the spin wave dispersion in the polarized state, which is consistent with the observation of a two-dimensional quantum critical point with the Bose-Einstein condensation of diluted free bosons.

Acoustic Rashba-Edelstein effect

船戸 匠*; 松尾 衛

Journal of Magnetism and Magnetic Materials, 540, p.168436_1 - 168436_7, 2021/12

https://doi.org/10.1016/j.jmmm.2021.168436

We theoretically study the mechanical induction of the spin density via the Rashba spin--orbit interaction (SOI). The spin density in the linear response to lattice distortion dynamics is calculated based on the microscopic theory. We reveal that there are two mechanisms of spin induction: one is the acoustic Edelstein effect (AEE) from the acceleration of the lattice dynamics and the other is caused by the Rashba spin--vorticity coupling (RSVC). We find that the AEE induces a more efficient spin-to-charge conversion in comparison with the conventional electric Edelstein effect. The induced spin density due to the RSVC is expressed as a Berry curvature-like quantity; therefore, it can be attributed to the spatial symmetry breaking due to the Rashba SOI. Our work demonstrates high-efficiency spin generation in Rashba systems.

Spin pumping of two-dimensional electron gas with Rashba and Dresselhaus spin-orbit interactions

山 正樹*; 立野 雅大*; 加藤 岳生*; 松尾 衛

Physical Review B, 104(5), p.054410_1 - 054410_9, 2021/08

https://doi.org/10.1103/PhysRevB.104.054410

We theoretically consider spin pumping in a junction between a ferromagnetic insulator (FI) and a two-dimensional electron gas (2DEG) in which the Rashba and Dresselhaus spin-orbit interactions coexist. Using second-order perturbation theory, we derive an increase in linewidth in the case of an interfacial exchange coupling in a ferromagnetic resonance (FMR) experiment. We clarify how the enhancement of Gilbert damping depends on the resonant frequency and spin orientation of the FI. We show that this setup of an FMR experiment can provide information on the spin texture of 2DEG at the Fermi surface.

Asymmetric quantum shot noise in magnon transport

仲田 光樹; 大沼 悠一*; 松尾 衛*

Physical Review B, 99(13), p.134403_1 - 134403_7, 2019/04

AA2019-0013.pdf:0.42MB

https://doi.org/10.1103/PhysRevB.99.134403

マグノン流に内在する量子力学的性質「量子ゆらぎ物性」をスピン流雑音の観点から理論的に研究し、マグノン流の非可換性由来の非対称マグノン流量子雑音を解明した。

新しい磁性半導体の開発に成功

前川 禎通

セラミックス, 46, P. 1072, 2011/12

http://www.ceramic.or.jp/ihensyub/topics/topics2011.12.pdf

Jin Changqing教授(中国科学院),植村泰朋教授(米コロンビア大学),前川禎通センター長(日本原子力研究開発機構・先端基礎研究センター)及び内田慎一教授(東京大学理学系研究科)等の国際共同研究グループは、新しい磁性半導体であるLi(Zn,Mn)Asの開発に成功した。この物質は、従来の磁性半導体とは異なり磁気的性質と電気的性質を独立に制御でき、また将来の物質開発によりp型とn型の両方の性質を取り得ると予想されることから、磁性半導体によるp-n接合への道を拓く可能性があり、スピントロニクスの応用領域を大きく広げることが期待される。今回作成された材料では、リチウムが過剰な場合においてLi(Zn,Mn)Asに強磁性が発現してp型半導体となることがわかった。また、材料が均一な磁性を示すことを、ミュオンスピン緩和測定により明らかにし、スピンを効率よく操作できることを確認した。これらはLi(Zn,Mn)Asが今後のエレクトロニクス材料として極めて有望であることを示している。この研究は原子力機構・先端基礎研究センターの黎明研究制度による共同研究で行われた。

Spatial and pulse shape dependence of K source from high contrast fs laser plasmas in regime of Relativistic Engineering

Chen, L.-M.; Koga, J. K.; 神門 正城; 小瀧 秀行; 中島 一久; Bulanov, S. V.; 田島 俊樹; Xu, M. H.*; Li, Y.-T.*; Dong, Q. L.*; et al.

no journal, , 

チタンサファイアレーザーと銅フォイルの相互作用を硬X線計測により調べた。硬X線分光とKX線への変換効率()について、パルス幅(60fs600fs),レーザーエネルギー(60mJ600mJ),ターゲット位置を変えて計測を行った。集光強度I110W/cmでは、変換効率は強度を増すにつれ上昇し、最大110が集光強度=110W/cmのときに得られた。集光位置は、集光強度が10W/cm10W/cmの範囲で大きく変えると、2つのX線ピークがあることがわかった。1つは最良の集光点において得られ、もう1つは、そこから離れて集光強度にして10W/cmとなる点である。最近発表された成果と比較すると、それぞれのピークは、異なるエネルギー吸収の機構によって説明できる。さらに、パルス圧縮器の回折格子対の間隔を変えることにより、負のチャープにした場合に正のチャープを与えた場合よりも7倍のX線への変換効率を得た。これらは、真空加熱による効果であると予測され、プリプラズマの制御が相対論的フェムト秒領域でのX線発生の制御の鍵となることがわかった。

バルクマグノン流雑音

仲田 光樹; 大沼 悠一*; 松尾 衛*

no journal, , 

Keldysh形式(Green関数法)を用い、Fermi粒子系(電子系)に対する「Boltzmann-Langevinアプローチ」をBose粒子系(マグノン系)に発展・適用させ、量子統計性に依らない普遍的輸送物性をショットノイズ(非平衡雑音)の観点から明らかにする。