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横井 直人*; 齊藤 英治
Journal of Magnetism and Magnetic Materials, 545, p.168673_1 - 168673_12, 2022/03
被引用回数:0 パーセンタイル:0(Materials Science, Multidisciplinary)We propose a dual gravitational theory corresponding to isotropic ferromagnetic systems based on the holographic duality, and establish the holographic dictionary between physical quantities in ferromagnets and the gravitational theory. Utilizing the holographic dictionary, the holographic calculation in the dual gravitational theory is shown to reproduce thermodynamics of ferromagnets including ferromagnetic phase transitions and low-temperature behaviors originating from magnons and conduction electrons. We further derive the equation for magnetization dynamics in ferromagnets from the equations for scalar fields and non-abelian gauge fields on charged black holes in the dual gravitational theory. From these results, the holographic duality is expected to give a new guiding principle to explore new phenomena in spintronics and magnonics based on the gravitational perspective.
横井 直人*; 齊藤 英治
Physical Review B, 103(13), p.134401_1 - 134401_8, 2021/04
被引用回数:1 パーセンタイル:7.92(Materials Science, Multidisciplinary)Multimode magnon dynamics affected by demagnetizing fields has been discussed in terms of a Hamiltonian approach. In the multimode dynamics involving magnetization relaxation, inter-mode correlation of magnons is found to be formed spontaneously. The correlation suppresses the transverse magnetization dynamics, giving rise to depolarization correlation (DPC) of magnons. DPC may subsist in equilibrium distribution at finite temperatures.
横井 直人*; 佐藤 浩司*; 齊藤 英治
Physical Review D, 100(10), p.106012_1 - 106012_9, 2019/11
被引用回数:2 パーセンタイル:13.91(Astronomy & Astrophysics)We introduce a new approach to understand magnetization dynamics in ferromagnets based on the holographic realization of ferromagnets. A Landau-Lifshitz equation describing the magnetization dynamics is derived from a Yang-Mills equation in the dual gravitational theory, and temperature dependences of the spin-wave stiffness and spin transfer torque appearing in the holographic Landau-Lifshitz equation are investigated by the holographic approach. The results are consistent with the known properties of magnetization dynamics in ferromagnets with conduction electrons.
Lustikova, J.*; 塩見 雄毅*; 横井 直人*; 壁谷 典幸*; 木村 憲彰*; 家永 紘一郎*; 金子 真一*; 大熊 哲*; 高橋 三郎*; 齊藤 英治
Nature Communications (Internet), 9, p.4922_1 - 4922_6, 2018/11
被引用回数:30 パーセンタイル:83.87(Multidisciplinary Sciences)A rectenna, standing for a rectifying antenna, is an apparatus which generates d.c. electricity from electric fluctuations. It is expected to realize wireless power transmission as well as energy harvesting from environmental radio waves. To realize such rectification, devices that are made up of internal atomic asymmetry such as an asymmetric junction have been necessary so far. Here we report a material that spontaneously generates electricity by rectifying environmental fluctuations without using atomic asymmetry. The sample is a common superconductor without lowered crystalline symmetry, but, just by putting it in an asymmetric magnetic environment, it turns into a rectifier and starts generating electricity. Superconducting vortex strings only annihilate and nucleate at surfaces, and this allows the bulk electrons to feel surface fluctuations in an asymmetric environment: a vortex rectenna. The rectification and generation can be switched on and off with only a slight change in temperature or external magnetic fields.
横井 直人*; 石原 雅文*; 佐藤 浩司*; 齊藤 英治
Physical Review D, 93(2), p.026002_1 - 026002_6, 2016/01
被引用回数:16 パーセンタイル:60.37(Astronomy & Astrophysics)A holographic realization for ferromagnetic systems is constructed. Owing to the holographic dictionary proposed on the basis of this realization, we obtain relevant thermodynamic quantities such as magnetization, magnetic susceptibility, and free energy. This holographic model reproduces the behavior of the mean field theory near the critical temperature. At low temperatures, the results automatically incorporate the contributions from spin wave excitations and conduction electrons.
松尾 衛; 家田 淳一; 針井 一哉; 大沼 悠一*; 横井 直人*; 前川 禎通
no journal, ,
本講演では、結晶中の転移(刃状転移、螺旋転移)のスピン流へ の影響を調べ、転移によってスピンホール効果が引き起こされるこ とを理論的に示す。転移のある結晶格子のダイナミクスは、ゲージ場として記述でき ることが知られており、刃状転移や螺旋転移はカルタンの捩率 とよばれる幾何学量によって表される。我々は、このゲージ場中の 電子の基礎方程式を導き、捩率とスピンが相互作用することを示す。