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Publications (6 of 6) Show all publications
Rybakov, F. N. & Kiselev, N. S. (2019). Chiral magnetic skyrmions with arbitrary topological charge. Physical Review B, 99(6), Article ID 064437.
Open this publication in new window or tab >>Chiral magnetic skyrmions with arbitrary topological charge
2019 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 6, article id 064437Article in journal (Refereed) Published
Abstract [en]

We show that continuous and spin-lattice models of chiral ferro- and antiferromagnets provide the existence of an infinite number of stable soliton solutions of any integer topological charge. A detailed description of the morphology of new skyrmions and the corresponding energy dependencies are provided. The considered model is general, and is expected to predict a plethora of particlelike states which may occur in various chiral magnets including ultrathin films, e.g., PdFe/Ir(111), rhombohedral GaV4S8 semiconductor, B20-type alloys as Mn1-xFexGe, Mn1-xFexSi, Fe1-xCoxSi, Cu2OSeO3, and acentric tetragonal Heusler compounds.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2019
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-246252 (URN)10.1103/PhysRevB.99.064437 (DOI)000459933900005 ()2-s2.0-85062506079 (Scopus ID)
Note

QC 20190402

Available from: 2019-04-02 Created: 2019-04-02 Last updated: 2019-04-04Bibliographically approved
Bommer, J. D. S., Zhang, H., Gul, O., Nijholt, B., Wimmer, M., Rybakov, F. N., . . . Kouwenhoven, L. P. (2019). Spin-Orbit Protection of Induced Superconductivity in Majorana Nanowires. Physical Review Letters, 122(18), Article ID 187702.
Open this publication in new window or tab >>Spin-Orbit Protection of Induced Superconductivity in Majorana Nanowires
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2019 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 122, no 18, article id 187702Article in journal (Refereed) Published
Abstract [en]

Spin-orbit interaction (SOI) plays a key role in creating Majorana zero modes in semiconductor nanowires proximity coupled to a superconductor. We track the evolution of the induced superconducting gap in InSb nanowires coupled to a NbTiN superconductor in a large range of magnetic field strengths and orientations. Based on realistic simulations of our devices, we reveal SOI with a strength of 0.15-0.35 eV angstrom. Our approach identifies the direction of the spin-orbit field, which is strongly affected by the superconductor geometry and electrostatic gates.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2019
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-252376 (URN)10.1103/PhysRevLett.122.187702 (DOI)000467404500003 ()2-s2.0-85065836132 (Scopus ID)
Note

QC 20190718

Available from: 2019-07-18 Created: 2019-07-18 Last updated: 2019-10-10Bibliographically approved
Rybakov, F. N., Garaud, J. & Babaev, E. (2019). Stable Hopf-Skyrme topological excitations in the superconducting state. Physical Review B, 100(9), Article ID 094515.
Open this publication in new window or tab >>Stable Hopf-Skyrme topological excitations in the superconducting state
2019 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, no 9, article id 094515Article in journal (Refereed) Published
Abstract [en]

At large scales, magnetostatics of superconductors is described by a massive vector field theory: the London model. The magnetic field cannot penetrate into the bulk unless quantum vortices are formed. These are topological excitations characterized by an invariant: the phase winding. The London model dictates that loops of such vortices are not stable because the kinetic energy of superflow and the magnetic energy are smaller, the smaller vortex loops are. We demonstrate that in two-component superconductors, under certain conditions, such as the proximity to pair-density-wave instabilities, the hydromagnetostatics of the superconducting state and topological excitation changes dramatically: the excitations acquire the form of stable vortex loops and knots characterized by the different topological invariant: the Hopf index and hence termed hopfions. This demonstrates that magnetic properties in a superconducting state can be dramatically different from those of a London's massive vector field theory.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2019
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-261010 (URN)10.1103/PhysRevB.100.094515 (DOI)000485189900003 ()
Note

QC 20191003

Available from: 2019-10-03 Created: 2019-10-03 Last updated: 2019-10-03Bibliographically approved
Zheng, F., Rybakov, F. N., Borisov, A. B., Song, D., Wang, S., Li, Z.-A., . . . Dunin-Borkowski, R. E. (2018). Experimental observation of chiral magnetic bobbers in B20-type FeGe. Nature Nanotechnology, 13(6), 451-+
Open this publication in new window or tab >>Experimental observation of chiral magnetic bobbers in B20-type FeGe
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2018 (English)In: Nature Nanotechnology, ISSN 1748-3387, E-ISSN 1748-3395, Vol. 13, no 6, p. 451-+Article in journal (Refereed) Published
Abstract [en]

Chiral magnetic skyrmions(1,2) are nanoscale vortex-like spin textures that form in the presence of an applied magnetic field in ferromagnets that support the Dzyaloshinskii-Moriya interaction (DMI) because of strong spin-orbit coupling and broken inversion symmetry of the crystal(3,4). In sharp contrast to other systems(5,6) that allow for the formation of a variety of two-dimensional (2D) skyrmions, in chiral magnets the presence of the DMI commonly prevents the stability and coexistence of topological excitations of different types(7). Recently, a new type of localized particle-like object-the chiral bobber (ChB)-was predicted theoretically in such materials(8). However, its existence has not yet been verified experimentally. Here, we report the direct observation of ChBs in thin films of B20-type FeGe by means of quantitative off-axis electron holography (EH). We identify the part of the temperature-magnetic field phase diagram in which ChBs exist and distinguish two mechanisms for their nucleation. Furthermore, we show that ChBs are able to coexist with skyrmions over a wide range of parameters, which suggests their possible practical applications in novel magnetic solid-state memory devices, in which a stream of binary data bits can be encoded by a sequence of skyrmions and bobbers.

Place, publisher, year, edition, pages
NATURE PUBLISHING GROUP, 2018
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-231198 (URN)10.1038/s41565-018-0093-3 (DOI)000434715700012 ()29632400 (PubMedID)2-s2.0-85045089631 (Scopus ID)
Funder
EU, European Research Council, 320832Swedish Research Council, 642-2013-7837
Note

QC 20180720

Available from: 2018-07-20 Created: 2018-07-20 Last updated: 2018-07-20Bibliographically approved
Du, H., Zhao, X., Rybakov, F. N., Borisov, A. B., Wang, S., Tang, J., . . . Tian, M. (2018). Interaction of Individual Skyrmions in a Nanostructured Cubic Chiral Magnet. Physical Review Letters, 120(19), Article ID 197203.
Open this publication in new window or tab >>Interaction of Individual Skyrmions in a Nanostructured Cubic Chiral Magnet
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2018 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 120, no 19, article id 197203Article in journal (Refereed) Published
Abstract [en]

We report direct evidence of the field-dependent character of the interaction between individual magnetic skyrmions as well as between skyrmions and edges in B20-type FeGe nanostripes observed by means of high-resolution Lorentz transmission electron microscopy. It is shown that above certain critical values of an external magnetic field the character of such long-range skyrmion interactions changes from attraction to repulsion. Experimentally measured equilibrium inter-skyrmion and skyrmion-edge distances as a function of the applied magnetic field shows quantitative agreement with the results of micromagnetic simulations. The important role of demagnetizing fields and the internal symmetry of three-dimensional magnetic skyrmions are discussed in detail.

Place, publisher, year, edition, pages
American Physical Society, 2018
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-230522 (URN)10.1103/PhysRevLett.120.197203 (DOI)000432991900014 ()29799255 (PubMedID)2-s2.0-85047738204 (Scopus ID)
Funder
Swedish Research Council, 642-2013-7837Göran Gustafsson Foundation for Research in Natural Sciences and Medicine
Note

QC 20180724

Available from: 2018-07-24 Created: 2018-07-24 Last updated: 2018-07-24Bibliographically approved
Bessarab, P. F., Mueller, G. P., Lobanov, I. S., Rybakov, F. N., Kiselev, N. S., Jonsson, H., . . . Delin, A. (2018). Lifetime of racetrack skyrmions. Scientific Reports, 8, Article ID 3433.
Open this publication in new window or tab >>Lifetime of racetrack skyrmions
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2018 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 3433Article in journal (Refereed) Published
Abstract [en]

The skyrmion racetrack is a promising concept for future information technology. There, binary bits are carried by nanoscale spin swirls-skyrmions-driven along magnetic strips. Stability of the skyrmions is a critical issue for realising this technology. Here we demonstrate that the racetrack skyrmion lifetime can be calculated from first principles as a function of temperature, magnetic field and track width. Our method combines harmonic transition state theory extended to include Goldstone modes, with an atomistic spin Hamiltonian parametrized from density functional theory calculations. We demonstrate that two annihilation mechanisms contribute to the skyrmion stability: At low external magnetic field, escape through the track boundary prevails, but a crossover field exists, above which the collapse in the interior becomes dominant. Considering a Pd/Fe bilayer on an Ir(111) substrate as a well-established model system, the calculated skyrmion lifetime is found to be consistent with reported experimental measurements. Our simulations also show that the Arrhenius pre-exponential factor of escape depends only weakly on the external magnetic field, whereas the pre-exponential factor for collapse is strongly field dependent. Our results open the door for predictive simulations, free from empirical parameters, to aid the design of skyrmion-based information technology.

Place, publisher, year, edition, pages
NATURE PUBLISHING GROUP, 2018
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-224023 (URN)10.1038/s41598-018-21623-3 (DOI)000425590600057 ()29467438 (PubMedID)2-s2.0-85042361199 (Scopus ID)
Note

QC 20180323

Available from: 2018-03-23 Created: 2018-03-23 Last updated: 2018-03-23Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-3577-7966

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