Magnonic noise and Wiedemann-Franz law Article Swipe
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· 2018
· Open Access
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· DOI: https://doi.org/10.1103/physrevb.98.094430
· OA: W2809217746
We theoretically establish mutual relations among magnetic momentum, heat,\nand fluctuations of propagating magnons in a ferromagnetic insulating junction\nin terms of noise and the bosonic Wiedemann-Franz (WF) law. Using the\nSchwinger-Keldysh formalism, we calculate all transport coefficients of a noise\nspectrum for both magnonic spin and heat currents, and establish Onsager\nrelations between the thermomagnetic currents and the zero-frequency noise.\nMaking use of the magnonic WF law and the Seebeck coefficient in the\nlow-temperature limit, we theoretically discover universal relations, i.e.\nbeing independent of material parameters, for both the nonequilibrium and\nequilibrium noise, and show that each noise is described solely in terms of\nthermal conductance. Finally, we introduce a magnonic spin-analog of the Fano\nfactor, noise-to-current ratio, and demonstrate that the magnonic spin-Fano\nfactor reduces to a universal value in the low-temperature limit and it remains\nvalid even beyond a linear response regime.\n
