Thermodynamic transport theory of spin waves in ferromagnetic insulators

Basso, Vittorio; Ferraro, Elena; Piazzi, Marco

doi:10.1103/physrevb.94.144422

Cited by 33 publications

(45 citation statements)

References 53 publications

(120 reference statements)

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“…This in turn generates an intrinsic magnetization gradient [15,[62][63][64][65] along both directions, and that along the x direction ∂ x B * produces a magnon counter Hall current along the y direction. Then, the system reaches a new stationary state such that in-and out-flowing magnon currents along the y direction balance each other, and there is no total magnon current in this new quasiequilibrium state, i.e., j y = 0.…”

Section: B Thermal Hall Conductancementioning

confidence: 99%

Magnonic quantum Hall effect and Wiedemann-Franz law

2017

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We present a quantum Hall effect of magnons in two-dimensional clean insulating magnets at finite temperature. Through the Aharonov-Casher effect, a magnon moving in an electric field acquires a geometric phase and forms Landau levels in an electric field gradient of sawtooth form. At low temperatures, the lowest energy band being almost flat carries a Chern number associated with a Berry curvature. Appropriately defining the thermal conductance for bosons, we find that the magnon Hall conductances get quantized and show a universal thermomagnetic behavior, i.e., are independent of materials, and obey a Wiedemann-Franz law for magnon transport. We consider magnons with quadratic and linear (Dirac-like) dispersions. Finally, we show that our predictions are within experimental reach for ferromagnets and skyrmion lattices with current device and measurement techniques.

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Section: B Thermal Hall Conductancementioning

confidence: 99%

Magnonic quantum Hall effect and Wiedemann-Franz law

2017

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“…The applied temperature gradient ∂ x T induces a magnonic spin current for each magnon (σ =↑, ↓), j xσ = −L 12σ ∂ x T /T , which leads to an accumulation of each magnon at the boundaries and thereby builds up a non-uniform magnetization since two magnon modes are decoupled and do not interfere with each other in the AF. This generates an intrinsic magnetization gradient [71][72][73][78][79][80] …”

Section: B Thermomagnetic Relationsmentioning

confidence: 99%

“…II, the offdiagonal elements 76,77 similarly arise from the magnon counter-current by the thermally-induced magnetization gradient [71][72][73][78][79][80] …”

Section: Hall Conductances Of Magnonsmentioning

confidence: 99%

“…The considered electric field with the constant gradient can be realized by an electric skewharmonic potential 46 and, while being challenging, it may be realized by STM tips 82,83 . The resulting magnetization gradient from the applied thermal gradient plays a role of an effective magnetic field gradient and works as a nonequilibrium magnonic spin chemical potential [71][72][73]78,79 that has been established experimentally in Ref. [80].…”

Section: Estimates For Experimentsmentioning

confidence: 99%

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Magnonic topological insulators in antiferromagnets

et al. 2017

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Extending the notion of symmetry protected topological phases to insulating antiferromagnets (AFs) described in terms of opposite magnetic dipole moments associated with the magnetic Néel order, we establish a bosonic counterpart of topological insulators in semiconductors. Making use of the Aharonov-Casher effect, induced by electric field gradients, we propose a magnonic analog of the quantum spin Hall effect (magnonic QSHE) for edge states that carry helical magnons. We show that such up and down magnons form the same Landau levels and perform cyclotron motion with the same frequency but propagate in opposite direction. The insulating AF becomes characterized by a topological Z2 number consisting of the Chern integer associated with each helical magnon edge state. Focusing on the topological Hall phase for magnons, we study bulk magnon effects such as magnonic spin, thermal, Nernst, and Ettinghausen effects, as well as the thermomagnetic properties of helical magnon transport both in topologically trivial and nontrivial bulk AFs and establish the magnonic Wiedemann-Franz law. We show that our predictions are within experimental reach with current device and measurement techniques.

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“…Thomson relation Π = T S Π = T S which can be understood as follows 144 ; the applied temperature difference produces a magnon current and consequently a magnetization difference [145][146][147] that induces a counter current. Thus, the system reaches a new quasi-equilibrium steady state where magnon currents no longer flow.…”

Section: Electronmentioning

confidence: 99%

Spin currents and magnon dynamics in insulating magnets

Nakata¹,

Simon²,

Loss³

2017

J. Phys. D: Appl. Phys.

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Nambu-Goldstone theorem provides gapless modes to both relativistic and nonrelativistic systems. The Nambu-Goldstone bosons in insulating magnets are called magnons or spin-waves and play a key role in magnetization transport. We review here our past works on magnetization transport in insulating magnets and also add new insights, with a particular focus on magnon transport. We summarize in detail the magnon counterparts of electron transport, such as the Wiedemann-Franz law, the Onsager reciprocal relation between the Seebeck and Peltier coefficients, the Hall effects, the superconducting state, the Josephson effects, and the persistent quantized current in a ring to list a few. Focusing on the electromagnetism of moving magnons, i.e., magnetic dipoles, we theoretically propose a way to directly measure magnon currents. As a consequence of the Mermin-WagnerHohenberg theorem, spin transport is drastically altered in one-dimensional antiferromagnetic (AF) spin-1/2 chains; where the Néel order is destroyed by quantum fluctuations and a quasiparticle magnon-like picture breaks down. Instead, the low-energy collective excitations of the AF spin chain are described by a Tomonaga-Luttinger liquid (TLL) which provides the spin transport properties in such antiferromagnets some universal features at low enough temperature. Finally, we enumerate open issues and provide a platform to discuss the future directions of magnonics.PACS numbers: Review article for special issue on magnonics from J. Phys. D.

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Thermodynamic transport theory of spin waves in ferromagnetic insulators

Cited by 33 publications

References 53 publications

Magnonic quantum Hall effect and Wiedemann-Franz law

Magnonic quantum Hall effect and Wiedemann-Franz law

Magnonic topological insulators in antiferromagnets

Spin currents and magnon dynamics in insulating magnets

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