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Magnonic noise and Wiedemann-Franz law

マグノン流雑音のウィーデマン-フランツ則

仲田 光樹  ; 大沼 悠一*; 松尾 衛*

Nakata, Koki; Onuma, Yuichi*; Matsuo, Mamoru*

強磁性絶縁体中のマグノンがもたらすスピン流/熱流に着目し、物質によらない「ゆらぎの普遍的熱磁気関係式」を紹介する。マグノン輸送に内在する量子統計力学的効果「ゆらぎ」を、マグノン流ノイズ(雑音)の視点から従来のマグノンWiedemann-Franz則に取り込み、「熱-磁気-ゆらぎ」三者を紡ぐ「ゆらぎのマグノンWiedemann-Franz則」を提示する。さらに、熱ノイズ(平衡ノイズ)と比較して非平衡ノイズが支配的となるマグノンショットノイズ領域に着目し、線形応答領域のみならず非線形応答領域においても成立するスピンFano因子の普遍的なふるまいを紹介する。

We theoretically establish mutual relations among magnetic momentum, heat, and fluctuations of propagating magnons in a ferromagnetic insulating junction in terms of noise and the bosonic Wiedemann-Franz (WF) law. Using the Schwinger-Keldysh formalism, we calculate all transport coefficients of a noise spectrum for both magnonic spin and heat currents, and establish Onsager relations between the thermomagnetic currents and the zero-frequency noise. Making use of the magnonic WF law and the Seebeck coefficient in the low-temperature limit, we theoretically discover universal relations, i.e. being independent of material parameters, for both the nonequilibrium and equilibrium noise, and show that each noise is described solely in terms of thermal conductance.

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パーセンタイル:59.67

分野:Materials Science, Multidisciplinary

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