Stimulated thermalization of a parametrically driven magnon gas as a prerequisite for Bose-Einstein magnon condensation

Clausen, Peter; Bozhko, Dmytro A.; Vasyuchka, Vitaliy I.; Hillebrands, B.; Melkov, G. A.; Serga, Alexander A.

doi:10.1103/physrevb.91.220402

Cited by 34 publications

(56 citation statements)

References 24 publications

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“…Related studies have also explored Josephson spin currents between magnons condensates [7]. Experimental studies have suggested that the temporal decrease of magnon condensates is associated with SSF [8].In the absence of magnetic fields, SSF is indeed an intriguing possibility because its realization would allow spin currents to propagate without significant losses over long distances. These spin transport properties may be useful for low-dissipation interconnects, spin logic devices, and non-volatile magnetic memory devices.…”

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confidence: 99%

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Spin Superfluidity and Long-Range Transport in Thin-Film Ferromagnets

2015

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In ferromagnets, magnons may condense into a single quantum state. Analogous to superconductors, this quantum state may support transport without dissipation. Recent works suggest that longitudinal spin transport through a thin-film ferromagnet is an example of spin superfluidity. Although intriguing, this tantalizing picture ignores long-range dipole interactions; we demonstrate that such interactions dramatically affect spin transport. In single-film ferromagnets, "spin superfluidity" only exists at length scales (a few hundred nanometers in yttrium iron garnet) somewhat larger than the exchange length. Over longer distances, dipolar interactions destroy spin superfluidity. Nevertheless, we predict re-emergence of spin superfluidity in tri-layer ferromagnet-normal metal-ferromagnet films of ∼ 1 µm in size. Such systems also exhibit other types of long-range spin transport in samples several micrometers in size.When matter enters a superfluid phase, it behaves like a fluid with zero viscosity and can support currents without dissipation. It has been suggested that certain ferromagnets may exhibit spin superfluidity (SSF) [1][2][3]. The superfluid spin-drag properties induced by spin transfer and spin pumping (SP) in a normal metal-ferromagnetnormal metal system have recently been computed [4][5][6]. Related studies have also explored Josephson spin currents between magnons condensates [7]. Experimental studies have suggested that the temporal decrease of magnon condensates is associated with SSF [8].In the absence of magnetic fields, SSF is indeed an intriguing possibility because its realization would allow spin currents to propagate without significant losses over long distances. These spin transport properties may be useful for low-dissipation interconnects, spin logic devices, and non-volatile magnetic memory devices. Our work demonstrates that SSF can exist in thin-film ferromagnetic systems, but two ferromagnets (rather than one) are required to cancel long-range dipole interactions. We do not observe signatures of long-range SSF in singlefilm ferromagnets.Recent works have hypothesized that easy-plane ferromagnetic thin films exhibit SSF. In such systems, a monotonously precessing magnetization leads to metastable spin-current-carrying states whose topological properties protect against dissipation [3]. Spin relaxation induces a finite resistance proportional to the system size [4]. Nevertheless, ferromagnetic insulators (FIs) have exceptionally low spin dissipation rates, and the spin supercurrent decays over a large length scale. Furthermore, the spin-relaxation-induced algebraic decay of the spin supercurrent significantly differs from the exponential decay of the spin current carried by spin waves [9]. Although magnetic anisotropy destroys the linear SSF response, the spin current is predicted to flow with negligible dissipation when the bias is sufficiently large [4,5].It is well known that long-range dipole interactions dramatically affect the spin-wave dispersion in thin films [10,11]. Low-energy ...

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confidence: 99%

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confidence: 99%

Spin Superfluidity and Long-Range Transport in Thin-Film Ferromagnets

2015

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“…(1)] among the nearest neighboring spins whose spin length are large enough 37,38 [i.e. S ≫ 1], we continue to apply microwave only to the right FI (P) and clarify the features of magnon transport 6,19 . We remark that in terms of spin variables, both correspond to a macroscopic coherent precession.…”

Section: Nonequilibrium Magnon Currentsmentioning

confidence: 99%

“…Since both magnon condensate and pumped magnons correspond to the macroscopic coherent precession 23 in terms of spin variables, it is expected that a similar 6,19 magnon current arises from microwave pumping. Therefore, based on the microscopic description of microwave pumping in Sec.…”

Section: 5mentioning

confidence: 99%

“…Third, magnons are quasiparticles (i.e., magnetic excitations) which are not conserved. Then, using microwave pumping [4][5][6][19][20][21] , they can be directly injected to FIs and their density controlled. A further advantage of magnons arises from the feature that magnons are bosonic excitations and as such they can form a macroscopic coherent 13 state, namely, a quasi-equilibrium Bose-Einstein condensate (BEC) [22][23][24][25] .…”

Section: Introductionmentioning

confidence: 99%

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Magnon transport through microwave pumping

2015

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We present a microscopic theory of magnon transport in ferromagnetic insulators (FIs). Using magnon injection through microwave pumping, we propose a way to generate magnon dc currents and show how to enhance their amplitudes in hybrid ferromagnetic insulating junctions. To this end focusing on a single FI, we first revisit microwave pumping at finite (room) temperature from the microscopic viewpoint of magnon injection. Next, we apply it to two kinds of hybrid ferromagnetic insulating junctions. The first is the junction between a quasi-equilibrium magnon condensate and magnons being pumped by microwave, while the second is the junction between such pumped magnons and noncondensed magnons. We show that quasi-equilibrium magnon condensates generate ac and dc magnon currents, while noncondensed magnons produce essentially a dc magnon current. The ferromagnetic resonance (FMR) drastically increases the density of the pumped magnons and enhances such magnon currents. Lastly, using microwave pumping in a single FI, we discuss the possibility that a magnon current through an Aharonov-Casher phase flows persistently even at finite temperature. We show that such a magnon current arises even at finite temperature in the presence of magnon-magnon interactions. Due to FMR, its amplitude becomes much larger than the condensed magnon current.

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New Dimension in Magnetism and Superconductivity: 3D and Curvilinear Nanoarchitectures

et al. 2021

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condensed matter physics, including cell membranes, [1] nematic crystals, [2,3] superfluids, [4] semiconductors, [5][6][7][8] ferromagnets, [9] and superconductors. [10,11] Currently, much attention is paid to strongly correlated electronic systems, for example, ferromagnets and superconductors, as they provide a unique tool to manipulate the topology of coexisting vector and scalar fields, associated with geometries of conventional systems.Until recently, in the case of magnetism, the influence of the geometry on the spin vector fields was addressed primarily by the design of the sample boundaries. This approach naturally brings the shape anisotropy to the system and leads to the formation of specific spin textures, for example, magnetic vortices [12] and antivortices [13] as well as provides control over the dynamics of the topologically nontrivial magnetic solitons. [14][15][16][17][18] This discussion also tackles the state of the art in modern experimental antiferromagnetism, where the design of the sample topography and boundaries allows to control the domain wall states. [19][20][21][22] With the development of novel fabrication techniques allowing to realize complex 3D architectures, not only the boundary effects but also the extrinsic geometrical properties (e.g., local curvatures) can be addressed rigorously for the case of ferromagnets [23][24][25][26][27] as well as superconductors. [28][29][30] The explored effects are directly related to the interplay between the Traditionally, the primary field, where curvature has been at the heart of research, is the theory of general relativity. In recent studies, however, the impact of curvilinear geometry enters various disciplines, ranging from solid-state physics over soft-matter physics, chemistry, and biology to mathematics, giving rise to a plethora of emerging domains such as curvilinear nematics, curvilinear studies of cell biology, curvilinear semiconductors, superfluidity, optics, 2D van der Waals materials, plasmonics, magnetism, and superconductivity. Here, the state of the art is summarized and prospects for future research in curvilinear solid-state systems exhibiting such fundamental cooperative phenomena as ferromagnetism, antiferromagnetism, and superconductivity are outlined. Highlighting the recent developments and current challenges in theory, fabrication, and characterization of curvilinear micro-and nanostructures, special attention is paid to perspective research directions entailing new physics and to their strong application potential. Overall, the perspective is aimed at crossing the boundaries between the magnetism and superconductivity communities and drawing attention to the conceptual aspects of how extension of structures into the third dimension and curvilinear geometry can modify existing and aid launching novel functionalities. In addition, the perspective should stimulate the development and dissemination of research and development oriented techniques to facilitate rapid transitions from laboratory demonstrations to industry-...

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Stimulated thermalization of a parametrically driven magnon gas as a prerequisite for Bose-Einstein magnon condensation

Cited by 34 publications

References 24 publications

Spin Superfluidity and Long-Range Transport in Thin-Film Ferromagnets

Spin Superfluidity and Long-Range Transport in Thin-Film Ferromagnets

Magnon transport through microwave pumping

New Dimension in Magnetism and Superconductivity: 3D and Curvilinear Nanoarchitectures

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