51 research outputs found
Ground-state multiquantum vortices in rotating two-species superfluids
We show numerically that a rotating, harmonically trapped mixture of two
Bose-Einstein-condensed superfluids can, contrary to its single-species
counterpart, contain a multiply quantized vortex in the ground state of the
system. This giant vortex can occur without any accompanying single-quantum
vortices, may either be coreless or have an empty core, and can be realized in
a Rb-K Bose-Einstein condensate. Our results not only provide a
rare example of a stable, solitary multiquantum vortex but also reveal exotic
physics stemming from the coexistence of multiple, compositionally distinct
condensates in one system.Comment: 6 pages, 4 color figures; identical in content to the published
articl
Skyrmionic vortex lattices in coherently coupled three-component Bose-Einstein condensates
We show numerically that a harmonically trapped and coherently Rabi-coupled
three-component Bose-Einstein condensate can host unconventional vortex
lattices in its rotating ground state. The discovered lattices incorporate
square and zig-zag patterns, vortex dimers and chains, and doubly quantized
vortices, and they can be quantitatively classified in terms of a skyrmionic
topological index, which takes into account the multicomponent nature of the
system. The exotic ground-state lattices arise due to the intricate interplay
of the repulsive density-density interactions and the Rabi couplings as well as
the ubiquitous phase frustration between the components. In the frustrated
state, domain walls in the relative phases can persist between some components
even at strong Rabi coupling, while vanishing between others. Consequently, in
this limit the three-component condensate effectively approaches a
two-component condensate with only density-density interactions. At
intermediate Rabi coupling strengths, however, we face unique vortex physics
that occurs neither in the two-component counterpart nor in the purely
density-density-coupled three-component system.Comment: 13 pages, 16 color figures; v2 is identical in content to the
published articl
Emergent phenomena in multicomponent superconductivity: an introduction to the focus issue
Multicomponent superconductivity is a novel quantum phenomenon in many different superconducting materials, such as multiband ones in which different
superconducting gaps open in different Fermi surfaces, films engineered at the atomic scale to enter the quantum confined regime, multilayers, two-dimensional electron gases at the oxide interfaces, and complex materials in which different electronic orbitals or different carriers participate in the formation of the superconducting condensate. In all these systems the increased number of degrees of freedom of the multicomponent superconducting wave-function allows for emergent quantum effects that are otherwise unattainable in single-component superconductors. In this editorial paper we introduce the present focus issue,
exploring the complex but fascinating physics of multicomponent superconductivity
Effects of spatially engineered Dzyaloshinskii-Moriya interaction in ferromagnetic films
The Dzyaloshinskii-Moriya interaction (DMI) is a chiral interaction that
favors formation of domain walls. Recent experiments and ab initio calculations
show that there are multiple ways to modify the strength of the interfacially
induced DMI in thin ferromagnetic films with perpendicular magnetic anisotropy.
In this paper we reveal theoretically the effects of spatially varied DMI on
the magnetic state in thin films. In such heterochiral 2D structures we report
several emergent phenomena, ranging from the equilibrium spin canting at the
interface between regions with different DMI, over particularly strong
confinement of domain walls and skyrmions within high-DMI tracks, to advanced
applications such as domain tailoring nearly at will, design of magnonic
waveguides, and much improved skyrmion racetrack memory
Paths to collapse for isolated skyrmions in few-monolayer ferromagnetic films
Magnetic skyrmions are topological spin configurations in materials with
chiral Dzyaloshinskii-Moriya interaction (DMI), that are potentially useful for
storing or processing information. To date, DMI has been found in few bulk
materials, but can also be induced in atomically thin magnetic films in contact
with surfaces with large spin-orbit interactions. Recent experiments have
reported that isolated magnetic skyrmions can be stabilized even near room
temperature in few-atom thick magnetic layers sandwiched between materials that
provide asymmetric spin-orbit coupling. Here we present the minimum-energy path
analysis of three distinct mechanisms for the skyrmion collapse, based on ab
initio input and the performed atomic-spin simulations. We focus on the
stability of a skyrmion in three atomic layers of Co, either epitaxial on the
Pt(111) surface, or within a hybrid multilayer where DMI nontrivially varies
per monolayer due to competition between different symmetry-breaking from two
sides of the Co film. In laterally finite systems, their constrained geometry
causes poor thermal stability of the skyrmion toward collapse at the boundary,
which we show to be resolved by designing the high-DMI structure within an
extended film with lower or no DMI
Deflection of (anti)ferromagnetic skyrmions at heterochiral interfaces
Devising magnetic nanostructures with spatially heterogeneous
Dzyaloshinskii-Moriya interaction (DMI) is a promising pathway towards advanced
confinement and control of magnetic skyrmions in potential devices. Here we
discuss theoretically how a skyrmion interacts with a heterochiral interface
using micromagnetic simulations and analytic arguments. We show that a
heterochiral interface deflects the trajectory of ferromagnetic (FM) skyrmions,
and that the extent of such deflection is tuned by the applied spin-polarized
current and the difference in DMI across the interface. Further, we show that
this deflection is characteristic for the FM skyrmion, and is completely absent
in the antiferromagnetic (AFM) case. In turn, we reveal that the AFM skyrmion
achieves much higher velocities than its FM counterpart, yet experiences far
stronger confinement in nanoengineered heterochiral tracks, which reinforces
AFM skyrmions as a favorable choice for skyrmion-based devices
Manipulation of Magnetic Skyrmions by Superconducting Vortices in Ferromagnet-Superconductor Heterostructures
Dynamics of magnetic skyrmions in hybrid ferromagnetic films harbors novel
physical phenomena and holds promise for technological applications. In this
work, we discuss the behavior of magnetic skyrmions when coupled to
superconducting vortices in a ferromagnet-superconductor heterostructure. We
use numerical simulations and analytic arguments to reveal broader
possibilities for manipulating the skyrmion-vortex dynamic correlations in the
hybrid system, that are not possible in its separated constituents. We explore
the thresholds of particular dynamic phases, and quantify the phase diagram as
a function of the relevant material parameters, applied current and induced
magnetic torques. Finally, we demonstrate the broad and precise tunability of
the skyrmion Hall-angle in presence of vortices, with respect to currents
applied to either or both the superconductor and the ferromagnet within the
heterostructure
Spin textures in chiral magnetic monolayers with suppressed nearest-neighbor exchange
High tunability of two dimensional magnetic materials (by strain, gating,
heterostructuring or otherwise) provides unique conditions for studying
versatile magnetic properties and controlling emergent magnetic phases.
Expanding the scope of achievable magnetic phenomena in such materials is
important for both fundamental and technological advances. Here we perform
atomistic spin-dynamics simulations to explore the (chiral) magnetic phases of
atomic monolayers in the limit of suppressed first-neighbors exchange
interaction. We report the rich phase diagram of exotic magnetic
configurations, obtained for both square and honeycomb lattice symmetries,
comprising coexistence of ferromagnetic and antiferromagnetic spin-cycloids, as
well as multiple types of magnetic skyrmions. We perform a minimum-energy path
analysis for the skyrmion collapse to evaluate the stability of such
topological objects, and reveal that magnetic monolayers could be good
candidates to host the antiferromagnetic skyrmions that are experimentally
evasive to date
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