Stabilization and control of Majorana bound states with elongated skyrmions (original) (raw)
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We propose using a mobile magnetic domain wall as a host of zero-energy Majorana fermions in a spin-orbit coupled nanowire sandwiched by two ferromagnetic strips and deposited on an s-wave superconductor. The ability to control domain walls by thermal means allows to braid Majorana fermions nonintrusively, which obey non-Abelian statistics. The analytical solutions of Majorana fermions inside domain walls are obtained in the strong spin-orbit regime.
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Physical Review A, 2012
ABSTRACT Majorana fermions are promising candidates for storing and processing information in topological quantum computation. The ability to control such individual information carriers in trapped ultracold atomic Fermi gases is a novel theme in quantum information science. However, fermionic atoms are neutral and thus are difficult to manipulate. Here, we theoretically investigate the control of emergent Majorana fermions in one-dimensional spin-orbit coupled atomic Fermi gases. We discuss (i) how to move Majorana fermions by increasing or decreasing an effective Zeeman field, which acts like a solid state control voltage gate; and (ii) how to create a pair of Majorana fermions by adding a magnetic impurity potential. We discuss the experimental realization of our control scheme in an ultracold Fermi gas of 40^{40}40K atoms.
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Topological superconductors are associated with the appearance of Majorana bound states, with promising applications in topologically protected quantum computing. In this Letter, we study a system where a skyrmion crystal is interfaced with a normal metal. Through interfacial exchange coupling, spin fluctuations in the skyrmion crystal mediate an effective electron-electron interaction in the normal metal. We study superconductivity within a weak-coupling approach and solve gap equations both close to the critical temperature and at zero temperature. Special features in the effective electron-electron interaction due to the noncolinearity of the magnetic ground state yield topological superconductivity at the interface.
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The aim of this Tutorial is to give a pedagogical introduction into realizations of Majorana fermions, usually termed as Majorana bound states (MBSs), in condensed matter systems with magnetic textures. We begin by considering the Kitaev chain model of “spinless” fermions and show how two “half” fermions can appear at chain ends due to interactions. By considering this model and its two-dimensional generalization, we emphasize intricate relation between topological superconductivity and possible realizations of MBS. We further discuss how “spinless” fermions can be realized in more physical systems, e.g., by employing the spin-momentum locking. Next, we demonstrate how magnetic textures can be used to induce synthetic or fictitious spin–orbit interactions, and, thus, stabilize MBS. We describe a general approach that works for arbitrary textures and apply it to skyrmions. We show how MBS can be stabilized by elongated skyrmions, certain higher order skyrmions, and chains of skyrmion...
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Scientific Reports
Magnetic skyrmions are topologically-protected chiral nano-scale spin structures that offer low power and high-density functionalities for spintronic devices. They behave as particles that can be moved, created and annihilated. These characteristics make them promising information-carrying bits, hence a precise control of the skyrmion motion is essential. This study shows that stabilizing skyrmion is possible using a stepped nanowire geometry. The nanoconstriction dimension and materials properties are found to strongly affect the pinning, depinning and annihilation of the skyrmion. It is also observed that near the stepped region, the skyrmion slows down and its velocity changes direction before its stability. Moreover, a reduction of skyrmion size as it squeezes through the stepped region is observed. Our results will open a new strategy for the design and development of skyrmion-based devices.
Magnetic Skyrmions in Condensed Matter Physics
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Skyrmions were originally introduced in Particle Physics as a possible mechanism to explain the stability of particles. Lately the concept has been applied in Condensed Matter Physics to describe the newly discovered topologically protected magnetic configurations called the magnetic Skyrmions. This elementary review introduces the concept at a level suitable for beginning students of Physics.
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Physical Review Letters, 2020
It has been argued that fluctuations of fermion parity are harmful for the demonstration of non-Abelian anyonic statistics. Here, we demonstrate a striking exception in which such fluctuations are actively used. We present a theory of coherent electron transport from a tunneling tip into a Corbino geometry Josephson junction where four Majorana bound states (MBSs) rotate. While the MBSs rotate, electron tunneling happens from the tip to one of the MBSs thereby changing the fermion parity of the MBSs. The tunneling events in combination with the rotation allow us to identify a novel braiding operator that does not commute with the braiding cycles in the absence of tunneling, revealing the non-Abelian nature of MBSs. The time-averaged tunneling current exhibits resonances as a function of the tip voltage with a period that is a direct consequence of the interference between the non-commuting braiding operations. Our work opens up a possibility for utilizing parity non-conserving processes to control non-Abelian states.
Physical review applied, 2022
The mutual interaction between a chiral ferromagnetic disk with confined skyrmionic structures and a superconducting disk is studied. The interaction is accounted for by solving simultaneously the Brown and London equations. We find that for a superconductor under an applied uniform field, the stray field of the shielding currents can trigger switching between different skyrmionic states in the ferromagnet that is not possible without the superconductor. We discuss the effect of the different parameters on the results and some possible applications such as multivalued logic, storage, and skyrmionic metamaterials.
Skyrmion-vortex interactions in chiral-magnet/superconducting hybrid systems
Over the past decade, advances in material synthesis have allowed physicists to uncover a vast range of intriguing properties in low-dimensional quantum magnets. In particular, spin-orbit coupling (SOC) and interfacial symmetry breaking in various low-dimensional materials have enabled the formation of chiral spin textures, including nanoscale vortex-like twists in the local magnetization which we call skyrmions. Topological excitations of this nature are extremely stable against external perturbations and easy to manipulate via electromagnetic or thermal pulses. Consequently, they have attracted major interest due to their potential for storing information in small, energyefficient devices. Beyond these memory cell applications, combining spin topology with conventional superconductivity provides a fascinating platform from which to investigate new physical phenomena such as the emergence of anyonic quasi-particles obeying non-Abelian statistics, with immediate implications for topological quantum computation. Coupling between magnetic skyrmions and superconducting vortices is expected to generate a rich variety of physical phenomena, including complex screening current profiles and flux dynamics in the superconductor, skyrmion-induced vortex nucleation, and the emergence of hybrid topological solitons capable of non-local quantum information storage. In this thesis, we have performed systematic transport and magnetization studies of the physics arising from the interplay of chiral magnetism and superconductivity in low-dimensional hybrid systems. We combine stacks of Ir/Fe (x) /Co (y) /Pt metallic multilayers with thin superconducting Nb films, which allow us to independently tune each of the magnetic lengthscales in our heterostructures and hence modulate the interaction strengths between the topological excitations characteristic to each layer. Using a combination of ultra-sensitive magnetization, electrical transport and magnetic imaging techniques, we identify signatures of skyrmion-induced antivortex nucleation phenomena, Meissner screening currents in the superconductor (induced by the chiral spin topology) and antivortex-induced changes in the skyrmion radius. Our work provides the first glimpse of hybrid topological solitons in real space and paves the way to integrating such phenomena in future functional material architectures.