13,712 research outputs found
RKKY Interaction On Surfaces of Topological Insulators With Superconducting Proximity Effect
We consider the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between
magnetic impurities on the surface of a three-dimensional topological insulator
with proximity induced superconductivity. A superconductor placed on the top of
the topological insulator induces a gap in the surface electron states and
gives rise to a long-ranged in-plane antiferromagnetic RKKY interaction. This
interaction is frustrated due to strong spin-orbit coupling, decays as
for , where is the distance between two magnetic impurities and
the superconducting coherence length, and dominates over the
ferromagnetic and Dzyaloshinskii-Moriya type interactions for . We find
the condition for the Yu-Shiba-Rusinov intragap states that are bound to the
magnetic impurities.Comment: 5 pages, 3 figure
Designer quantum states of matter created atom-by-atom
With the advances in high resolution and spin-resolved scanning tunneling
microscopy as well as atomic-scale manipulation, it has become possible to
create and characterize quantum states of matter bottom-up, atom-by-atom. This
is largely based on controlling the particle- or wave-like nature of electrons,
as well as the interactions between spins, electrons, and orbitals and their
interplay with structure and dimensionality. We review the recent advances in
creating artificial electronic and spin lattices that lead to various exotic
quantum phases of matter, ranging from topological Dirac dispersion to complex
magnetic order. We also project future perspectives in non-equilibrium
dynamics, prototype technologies, engineered quantum phase transitions and
topology, as well as the evolution of complexity from simplicity in this newly
developing field
mSpace meets EPrints: a Case Study in Creating Dynamic Digital Collections
In this case study we look at issues involved in (a) generating dynamic digital libraries that are on a particular topic but span heterogeneous collections at distinct sites, (b) supplementing the artefacts in that collection with additional information available either from databases at the artefact's home or from the Web at large, and (c) providing an interaction paradigm that will support effective exploration of this new resource. We describe how we used two available frameworks, mSpace and EPrints to support this kind of collection building. The result of the study is a set of recommendations to improve the connectivity of remote resources both to one another and to related Web resources, and that will also reduce problems like co-referencing in order to enable the creation of new collections on demand
Voltage induced conversion of helical to uniform nuclear spin polarization in a quantum wire
We study the effect of bias voltage on the nuclear spin polarization of a
ballistic wire, which contains electrons and nuclei interacting via hyperfine
interaction. In equilibrium, the localized nuclear spins are helically
polarized due to the electron-mediated Ruderman-Kittel-Kasuya-Yosida (RKKY)
interaction. Focusing here on non-equilibrium, we find that an applied bias
voltage induces a uniform polarization, from both helically polarized and
unpolarized spins available for spin flips. Once a macroscopic uniform
polarization in the nuclei is established, the nuclear spin helix rotates with
frequency proportional to the uniform polarization. The uniform nuclear spin
polarization monotonically increases as a function of both voltage and
temperature, reflecting a thermal activation behavior. Our predictions offer
specific ways to test experimentally the presence of a nuclear spin helix
polarization in semiconducting quantum wires.Comment: 8 pages, 4 figure
Sensing Noncollinear Magnetism at the Atomic Scale Combining Magnetic Exchange and Spin-Polarized Imaging
Storing and accessing information in atomic-scale magnets requires magnetic
imaging techniques with single-atom resolution. Here, we show simultaneous
detection of the spin-polarization and exchange force, with or without the flow
of current, with a new method, which combines scanning tunneling microscopy and
non-contact atomic force microscopy. To demonstrate the application of this new
method, we characterize the prototypical nano-skyrmion lattice formed on a
monolayer of Fe/Ir(111). We resolve the square magnetic lattice by employing
magnetic exchange force microscopy, demonstrating its applicability to
non-collinear magnetic structures, for the first time. Utilizing
distance-dependent force and current spectroscopy, we quantify the exchange
forces in comparison to the spin-polarization. For strongly spin-polarized
tips, we distinguish different signs of the exchange force which we suggest
arises from a change in exchange mechanisms between the probe and a skyrmion.
This new approach may enable both non-perturbative readout combined with
writing by current-driven reversal of atomic-scale magnets
Lattice topology and spontaneous parametric down-conversion in quadratic nonlinear waveguide arrays
We analyze spontaneous parametric down-conversion in various experimentally
feasible 1D quadratic nonlinear waveguide arrays, with emphasis on the
relationship between the lattice's topological invariants and the biphoton
correlations. Nontrivial topology results in a nontrivial "winding" of the
array's Bloch waves, which introduces additional selection rules for the
generation of biphotons. These selection rules are in addition to, and
independent of existing control using the pump beam's spatial profile and phase
matching conditions. In finite lattices, nontrivial topology produces single
photon edge modes, resulting in "hybrid" biphoton edge modes, with one photon
localized at the edge and the other propagating into the bulk. When the single
photon band gap is sufficiently large, these hybrid biphoton modes reside in a
band gap of the bulk biphoton Bloch wave spectrum. Numerical simulations
support our analytical results.Comment: 11 pages, 12 figure
The Geometry of the Cholesteric Phase
We propose a construction of a cholesteric pitch axis for an arbitrary
nematic director field as an eigenvalue problem. Our definition leads to a
Frenet-Serret description of an orthonormal triad determined by this axis, the
director, and the mutually perpendicular direction. With this tool we are able
to compare defect structures in cholesterics, biaxial nematics, and smectics.
Though they all have similar ground state manifolds, the defect structures are
different and cannot be, in general, translated from one phase to the other.Comment: 5 pages, the full catastroph
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