2,191 research outputs found
Spin-Transfer and Exchange Torques in Ferromagnetic Superconductors
We consider how superconducting correlations influence spin-transfer torques
in ferromagnetic superconductors. It is demonstrated that there is a novel
torque arising from particle-hole interference that depends on the U(1) phase
associated with the superconducting order parameter. We also show that there is
an equilibrium exchange torque between two ferromagnetic superconductors in
contact via a normal metal mediated by Andreev states. The latter equilibrium
magnetic torque is also sensitive to spin-resolved phase differences in the
superconducting order parameters as well as to an externally applied phase
difference.Comment: 5 pages, 3 figures. Accepted for publication in PR
The Intrinsic Magnetization of Antiferromagnetic Textures
Antiferromagnets (AFMs) exhibit intrinsic magnetization when the order
parameter spatially varies. This intrinsic spin is present even at equilibrium
and can be interpreted as a twisting of the homogeneous AFM into a state with a
finite spin. Because magnetic moments couple directly to external magnetic
fields, the intrinsic magnetization can alter the dynamics of antiferromagnetic
textures under such influence. Starting from the discrete Heisenberg model, we
derive the continuum limit of the free energy of AFMs in the exchange
approximation and explicitly rederive that the spatial variation of the
antiferromagnetic order parameter is associated with an intrinsic magnetization
density. We calculate the magnetization profile of a domain wall and discuss
how the intrinsic magnetization reacts to external forces. We show
conclusively, both analytically and numerically, that a spatially inhomogeneous
magnetic field can move and control the position of domain walls in AFMs. By
comparing our model to a commonly used alternative parametrization procedure
for the continuum fields, we show that the physical interpretations of these
fields depend critically on the choice of parametrization procedure for the
discrete-to-continuous transition. This can explain why a significant amount of
recent studies of the dynamics of AFMs, including effective models that
describe the motion of antiferromagnetic domain walls, have neglected the
intrinsic spin of the textured order parameter.Comment: 12 pages, 7 figure
Equations of Motion and Frequency Dependence of Magnon-Induced Domain Wall Motion
Spin waves can induce domain wall motion in ferromagnets. We derive the
equations of motion for a transverse domain wall driven by spin waves. Our
calculations show that the magnonic spin-transfer torque does not cause
rotation-induced Walker breakdown. The amplitude of spin waves that are excited
by a localized microwave field depends on the spatial profile of the field and
the excitation frequency. By taking this frequency dependence into account, we
show that a simple one-dimensional model may reproduce much of the puzzling
frequency dependence observed in early numerical studies.Comment: 7 pages, 7 figure
Andreev reflection in altermagnets
Recent works have predicted materials featuring bands with a large
spin-splitting distinct from ferromagnetic and relativistically spin-orbit
coupled systems. Materials displaying this property are known as altermagnets
and feature a spin-polarized band structure reminiscent of a -wave
superconducting order parameter. We here consider the contact between an
altermagnet and a superconductor and determine how the altermagnetism affects
the fundamental process of Andreev reflection. We show that the resulting
charge conductance depends strongly on the interfacial orientation of the
altermagnet relative to the superconductor, displaying features similar to
normal metals or ferromagnets. The zero-bias conductance peaks present at the
interface in the -wave case are robust toward the presence of an
altermagnetic interaction. Moreover, the spin conductance can be increased by
more than an order of magnitude compared to its normal-state value. It also
changes its sign via the applied bias voltage. These results show how the
spin-anisotropic altermagnetic state can be probed by conductance spectroscopy
and how it offers voltage control over directionally dependent spin currents
that are strongly enhanced due to superconductivity.Comment: 18 pages, 6 figure
Josephson effect in altermagnets
The ability of magnetic materials to modify superconducting systems is an
active research area for possible applications in thermoelectricity, quantum
sensing, and spintronics. We consider the fundamental properties of the
Josephson effect in a third class of magnetic materials beyond ferromagnets and
antiferromagnets: altermagnets. We show that despite having no net
magnetization, altermagnets induce - oscillations. The decay length and
oscillation period of the Josephson coupling are qualitatively different from
ferromagnetic junctions and depend on the crystallographic orientation of the
altermagnet. The Josephson effect in altermagnets thus serves a dual purpose:
it acts as a signature that distinguishes altermagnetism from conventional
(anti)ferromagnetism and offers a way to tune the supercurrent via flow
direction anisotropy.Comment: 4 pages, 4 figure
Consequences of long-term infrastructure decisionsâthe case of self-healing roads and their CO2 emissions
What could be the reduction in greenhouse gas emissions if the conventional way of maintaining roads is changed? Emissions of greenhouse gases must be reduced if global warming is to be avoided, and urgent political and technological decisions should be taken. However, there is a lock-in in built infrastructures that is limiting the rate at which emissions can be reduced. Self-healing asphalt is a new type of technology that will reduce the need for fossil fuels over the lifetime of a road pavement, at the same time as prolonging the road lifespan. In this study we have assessed the benefits of using self-healing asphalt as an alternative material for road pavements employing a hybrid inputâoutput-assisted Life-Cycle Assessment, as only by determining the plausible scenarios of future emissions will policy makers identify pathways that might achieve climate change mitigation goals. We have concluded that self-healing roads could prevent a considerable amount of emissions and costs over the global road network: 16% lower emissions and 32% lower costs compared to a conventional road over the lifecycle
Superconducting proximity effect and long-ranged triplets in dirty metallic antiferromagnets
Antiferromagnets have no net spin-splitting on the scale of the
superconducting coherence length. Despite this, antiferromagnets have been
observed to suppress superconductivity in a similar way as ferromagnets, a
phenomenon that still lacks a clear understanding. We find that this effect can
be explained by the role of impurities in antiferromagnets. Using
quasiclassical Green's functions, we study the proximity effect and critical
temperature in diffusive superconductor-metallic antiferromagnet bilayers. The
non-magnetic impurities acquire an effective magnetic component in the
antiferromagnet. This not only reduces the critical temperature but also
separates the superconducting correlations into short-ranged and long-ranged
components, similar to ferromagnetic proximity systems.Comment: 5 pages, 4 figure
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