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Funato, Takumi*; Matsuo, Mamoru
Journal of Magnetism and Magnetic Materials, 540, p.168436_1 - 168436_7, 2021/12
Times Cited Count：3 Percentile：25.69(Materials Science, Multidisciplinary)Yamamoto, Tsuyoshi*; Kato, Takeo*; Matsuo, Mamoru
Physical Review B, 104(12), p.L121401_1 - L121401_5, 2021/09
Times Cited Count：5 Percentile：44.86(Materials Science, Multidisciplinary)Yama, Masaki*; Tatsuno, Masahiro*; Kato, Takeo*; Matsuo, Mamoru
Physical Review B, 104(5), p.054410_1 - 054410_9, 2021/08
Times Cited Count：7 Percentile：51.66(Materials Science, Multidisciplinary)Funato, Takumi*; Matsuo, Mamoru
Physical Review B, 104(6), p.L060412_1 - L060412_5, 2021/08
Times Cited Count：3 Percentile：27.71(Materials Science, Multidisciplinary)Nakata, Koki; Onuma, Yuichi*; Matsuo, Mamoru*
Physical Review B, 99(13), p.134403_1 - 134403_7, 2019/04
Times Cited Count：4 Percentile：22(Materials Science, Multidisciplinary)We study a frequency-dependent noise-to-current ratio for asymmetric, symmetric, and noncommutative current noise in a ferromagnetic insulating junction, and extract quantum-mechanical properties of magnon transport at low temperatures. We demonstrate that the noncommutative noise, which vanishes in the dc limit (i.e., a classical regime), increases monotonically as a function of frequency, and show that the noncommutative noise associated directly with quantum fluctuations of magnon currents breaks through the classical upper limit determined by the symmetric noise and realizes asymmetric quantum shot noise. Finally, we show that our theoretical predictions are within experimental reach with current device and measurement schemes while exploiting low temperatures. Our work provides a platform toward experimental access to quantum fluctuations of magnon currents.
Nakata, Koki; Onuma, Yuichi*; Matsuo, Mamoru*
Physical Review B, 98(9), p.094430_1 - 094430_8, 2018/09
Times Cited Count：11 Percentile：49.2(Materials Science, Multidisciplinary)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.
