1,983 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
Sequential Tunneling through Molecular Spin Rings
We consider electrical transport through molecules with Heisenberg-coupled
spins arranged in a ring structure in the presence of an easy-axis anisotropy.
The molecules are coupled to two metallic leads and a gate. In the charged
state of the ring, a Zener double-exchange mechanism links transport properties
to the underlying spin structure. This leads to a remarkable contact-site
dependence of the current, which for an antiferromagnetic coupling of the spins
can lead to a total suppression of the zero-bias conductance when the molecule
is contacted at adjacent sites.Comment: 4 pages, 3 figure
Conductance fluctuations in diffusive rings: Berry phase effects and criteria for adiabaticity
We study Berry phase effects on conductance properties of diffusive
mesoscopic conductors, which are caused by an electron spin moving through an
orientationally inhomogeneous magnetic field. Extending previous work, we start
with an exact, i.e. not assuming adiabaticity, calculation of the universal
conductance fluctuations in a diffusive ring within the weak localization
regime, based on a differential equation which we derive for the diffuson in
the presence of Zeeman coupling to a magnetic field texture. We calculate the
field strength required for adiabaticity and show that this strength is reduced
by the diffusive motion. We demonstrate that not only the phases but also the
amplitudes of the h/2e Aharonov-Bohm oscillations are strongly affected by the
Berry phase. In particular, we show that these amplitudes are completely
suppressed at certain magic tilt angles of the external fields, and thereby
provide a useful criterion for experimental searches. We also discuss Berry
phase-like effects resulting from spin-orbit interaction in diffusive
conductors and derive exact formulas for both magnetoconductance and
conductance fluctuations. We discuss the power spectra of the
magnetoconductance and the conductance fluctuations for inhomogeneous magnetic
fields and for spin-orbit interaction.Comment: 18 pages, 13 figures; minor revisions. To appear in Phys. Rev.
Correlations between Majorana fermions through a superconductor
We consider a model of ballistic quasi-one dimensional semiconducting wire
with intrinsic spin-orbit interaction placed on the surface of a bulk s-wave
superconductor (SC), in the presence of an external magnetic field. This setup
has been shown to give rise to a topological superconducting state in the wire,
characterized by a pair of Majorana-fermion (MF) bound states formed at the two
ends of the wire. Here we demonstrate that, besides the well-known direct
overlap-induced energy splitting, the two MF bound states may hybridize via
elastic correlated tunneling processes through virtual quasiparticles states in
the SC, giving rise to an additional energy splitting between MF states from
the same as well as from different wires.Comment: 7 pages, 3 figure
Proximity-induced Josephson -Junctions in Topological Insulators
We study two microscopic models of topological insulators in contact with an
-wave superconductor. In the first model the superconductor and the
topological insulator are tunnel coupled via a layer of scalar and of randomly
oriented spin impurities. Here, we require that spin-flip tunneling dominates
over spin-conserving one. In the second model the tunnel coupling is realized
by an array of single-level quantum dots with randomly oriented spins. It is
shown that the tunnel region forms a -junction where the effective order
parameter changes sign. Interestingly, due to the random spin orientation the
effective descriptions of both models exhibit time-reversal symmetry. We then
discuss how the proposed -junctions support topological superconductivity
without magnetic fields and can be used to generate and manipulate Kramers
pairs of Majorana fermions by gates
Topological Magnons and Edge States in Antiferromagnetic Skyrmion Crystals
Antiferromagnetic skyrmion crystals are magnetic phases predicted to exist in
antiferromagnets with Dzyaloshinskii-Moriya interactions. Their spatially
periodic noncollinear magnetic texture gives rise to topological bulk magnon
bands characterized by nonzero Chern numbers. We find topologically-protected
chiral magnonic edge states over a wide range of magnetic fields and
Dzyaloshinskii-Moriya interaction values. Moreover, and of particular
importance for experimental realizations, edge states appear at the lowest
possible energies, namely, within the first bulk magnon gap. Thus,
antiferromagnetic skyrmion crystals show great promise as novel platforms for
topological magnonics.Comment: 5 pages, 5 figure
Hardy-Littlewood-Sobolev Inequalities via Fast Diffusion Flows
We give a simple proof of the cases of the sharp
Hardy-Littlewood-Sobolev inequality for , and the sharp Logarithmic
Hardy-Littlewood-Sobolev inequality for via a monotone flow governed by
the fast diffusion equation
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