Superconductivity induced by interfacial coupling to magnons

Rohling, Niklas; Fjærbu, Eirik Løhaugen; Brataas, Arne

doi:10.1103/physrevb.97.115401

Cited by 35 publications

(58 citation statements)

References 43 publications

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“…The quantity σ in front of the electron operators on the second line is +1 for spin up and −1 for spin down. Fourier transforming the magnon and electron operators c iσ = 1 √ N k c kσ e −ik·r i then produces [13]…”

Section: B Diagonalization Of Subsystemsmentioning

confidence: 99%

Magnon-mediated superconductivity on the surface of a topological insulator

2020

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We study superconductivity on the surface of a topological insulator, mediated by magnetic fluctuations in an adjacent ferromagnetic or antiferromagnetic insulator. Superconductivity can arise from effective interactions between helical fermions induced by interfacial fermion-magnon interactions. For both ferromagnetic and antiferromagnetic insulators, these fermion-fermion interactions have the correct structure to facilitate pairing between particles located on the same side of the Fermi surface, also known as Amperean pairing. In antiferromagnets, the strength of the induced interactions can be enhanced by coupling the topological insulator asymmetrically to the two sublattices of the antiferromagnet. This effect is further amplified by next nearest neighbor frustration in the antiferromagnetic insulator. The enhancement makes the induced interactions significantly stronger in the antiferromagnetic case, as compared to the ferromagnetic case. These results indicate that an uncompensated antiferromagnetic interface might be a better candidate than a ferromagnetic interface for proximity-induced magnon-mediated superconductivity on the surface of a topological insulator. arXiv:1912.07607v2 [cond-mat.supr-con]

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Section: B Diagonalization Of Subsystemsmentioning

confidence: 99%

Magnon-mediated superconductivity on the surface of a topological insulator

2020

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“…These excitations are quasiparticles known as magnons. Theoretical predictions of electron-magnon interactions have shown that these can also induce effects such as superconductivity [1][2][3][4][5][6][7][8][9][10].Research interest in antiferromagnetic materials is surging [11,12]. This enthusiasm is due to the promising properties of antiferromagnets such as high resonance frequencies in the THz regime and a vanishing net magnetic moment.…”

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confidence: 99%

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Magnon-Mediated Indirect Exciton Condensation through Antiferromagnetic Insulators

et al. 2019

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Electrons and holes residing on the opposing sides of an insulating barrier and experiencing an attractive Coulomb interaction can spontaneously form a coherent state known as an indirect exciton condensate. We study a trilayer system where the barrier is an antiferromagnetic insulator. The electrons and holes here additionally interact via interfacial coupling to the antiferromagnetic magnons. We show that by employing magnetically uncompensated interfaces, we can design the magnon-mediated interaction to be attractive or repulsive by varying the thickness of the antiferromagnetic insulator by a single atomic layer. We derive an analytical expression for the critical temperature T c of the indirect exciton condensation. Within our model, anisotropy is found to be crucial for achieving a finite T c , which increases with the strength of the exchange interaction in the antiferromagnetic bulk. For realistic material parameters, we estimate T c to be around 7 K, the same order of magnitude as the current experimentally achievable exciton condensation where the attraction is solely due to the Coulomb interaction. The magnon-mediated interaction is expected to cooperate with the Coulomb interaction for condensation of indirect excitons, thereby providing a means to significantly increase the exciton condensation temperature range.Introduction.-Interactions between fermions result in exotic states of matter. Superconductivity is a prime example, where the negatively charged electrons can have an overall attractive coupling mediated by individual couplings to the vibrations, known as phonons, of the positively charged lattice. In addition to charge, the electron also has a spin degree of freedom. The electron spin can interact with localized magnetic moments through an exchange interaction exciting the magnetic moment by transfer of angular momentum. These excitations are quasiparticles known as magnons. Theoretical predictions of electron-magnon interactions have shown that these can also induce effects such as superconductivity [1][2][3][4][5][6][7][8][9][10].Research interest in antiferromagnetic materials is surging [11,12]. This enthusiasm is due to the promising properties of antiferromagnets such as high resonance frequencies in the THz regime and a vanishing net magnetic moment. Much of this research focuses on interactions involving magnons or spin waves at magnetic interfaces in hybrid structures. Examples of this are spin pumping [13-19], spin transfer [15, 20-22], and spin Hall magnetoresistance [23-28] at normal metal interfaces, and magnon-mediated superconductivity [9,10]. Recently, an experiment has also demonstrated spin transport in an antiferromagnetic insulator over distances up to 80 µm [29]. Moreover, antiferromagnetic materials are also of interest since it is believed that high-temperature superconductivity in cuprates is intricately linked to magnetic fluctuations near an antiferromagnetic Mott insulating phase [30,31]. Thus it is crucial to achieve a good understanding of antiferromagnetic magn...

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“…Here also it is important to note, as in the case without superconductivity, that Eqs. (16a)-(16c) and (17) are obtained assuming the continuous spectrum of three-dimensional wave vectors of the superconducting electrons, whereas for the electron-magnon heat conductance we include only a two-dimensional integral. As a result this overestimates G q−ph and underestimates the resulting crossover temperature.…”

Section: Theoretical Modelmentioning

confidence: 99%

“…The interfacial electron-magnon interaction strength can be quite large, and hence important for the thin film materials, as the recent work on superconductivity induced in a metal due to interfacial electron-magnon interaction [17], and spin transport across normal metal and ferromagnetic insulator [18,19] Pγ denotes the incident radiation power, which increases the electronic temperature by an amount ∆T from some initial temperature T dictated by the temperature of the baths. For a low and constant power Pγ , the magnitude of ∆T = Pγ /G tot th is dictated by the total heat conductance, G tot th , to the heat bath.…”

Section: Introductionmentioning

confidence: 99%

Thermalization of hot electrons via interfacial electron-magnon interaction

Chakraborty

Heikkilä

2019

Phys. Rev. B

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Recent work on layered structures of superconductors (S) or normal metals (N) in contact with ferromagnetic insulators (FI) has shown how the properties of the previous can be strongly affected by the magnetic proximity effect due to the static FI magnetization. Here we show that such structures can also exhibit a new electron thermalization mechanism due to the coupling of electrons with the dynamic magnetization, i.e., magnons in FI. We here study the heat flow between the two systems and find that in thin films the heat conductance due to the interfacial electron-magnon collisions can dominate over the well-known electron-phonon coupling below a certain characteristic temperature that can be straightforwardly reached with present-day experiments. We also study the role of the magnon band gap and the induced spin-splitting field induced in S on the resulting heat conductance and show that heat balance experiments can reveal information about such quantities in a way quite different from typical magnon spectroscopy experiments.

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Superconductivity induced by interfacial coupling to magnons

Cited by 35 publications

References 43 publications

Magnon-mediated superconductivity on the surface of a topological insulator

Magnon-mediated superconductivity on the surface of a topological insulator

Magnon-Mediated Indirect Exciton Condensation through Antiferromagnetic Insulators

Thermalization of hot electrons via interfacial electron-magnon interaction

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