Magnon-induced superconductivity in a topological insulator coupled to ferromagnetic and antiferromagnetic insulators

Hugdal, Henning G.; Rex, Sybille; Nogueira, Flavio S.; Sudbø, Asle

doi:10.1103/physrevb.97.195438

Cited by 28 publications

(33 citation statements)

References 49 publications

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“…We write ψ σ ≡ ψ σ (τ, r i ) and ψ σ ≡ ψ σ (τ , r j ), and the same convention for a, b, and J A, B (r i ). Let us first consider a general type of interface, and use H int in (8). The interface structure is then encoded in the spatial dependencies of J A, B (r i ).…”

Section: A One Interfacementioning

confidence: 99%

“…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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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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Magnon-Mediated Indirect Exciton Condensation through Antiferromagnetic Insulators

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“…In a subsequent related study, the cases of a TI coupled to a FMI and a TI coupled to an antiferromagnetic insulator (AFMI) were considered in Ref. [14]. Possible attractive interactions for both Amperean and BCStype pairing were found.…”

Section: Introductionmentioning

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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“…Conversely, magnons in the magnet can mediate electron-electron attraction in the conducting layer. The resulting magnon-mediated superconductivity has been investigated theoretically in normal metals [19,20] as well as topological insulators [21,22], and experimentally [23]. Magnon-mediated indirect exciton condensation has also been predicted recently [24].…”

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Enhancement of superconductivity mediated by antiferromagnetic squeezed magnons

et al. 2019

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We investigate theoretically magnon-mediated superconductivity in a heterostructure consisting of a normal metal and a two-sublattice antiferromagnetic insulator. The attractive electron-electron pairing interaction is caused by an interfacial exchange coupling with magnons residing in the antiferromagnet, resulting in p-wave, spin-triplet superconductivity in the normal metal. Our main finding is that one may significantly enhance the superconducting critical temperature by coupling the normal metal to only one of the two antiferromagnetic sublattices employing, for example, an uncompensated interface. Employing realistic material parameters, the critical temperature increases from vanishingly small values to values significantly larger than 1 K as the interfacial coupling becomes strongly sublattice-asymmetric. We provide a general physical picture of this enhancement mechanism based on the notion of squeezed bosonic eigenmodes. arXiv:1903.01470v3 [cond-mat.supr-con]

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Magnon-induced superconductivity in a topological insulator coupled to ferromagnetic and antiferromagnetic insulators

Cited by 28 publications

References 49 publications

Magnon-Mediated Indirect Exciton Condensation through Antiferromagnetic Insulators

Magnon-Mediated Indirect Exciton Condensation through Antiferromagnetic Insulators

Magnon-mediated superconductivity on the surface of a topological insulator

Enhancement of superconductivity mediated by antiferromagnetic squeezed magnons

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