34,579 research outputs found
Theoretical spin-wave dispersions in the antiferromagnetic phase AF1 of MnWO based on the polar atomistic model in P2
The spin wave dispersions of the low temperature antiferromagnetic phase
(AF1) MnWO have been numerically calculated based on the recently reported
non-collinear spin configuration with two different canting angles. A
Heisenberg model with competing magnetic exchange couplings and single-ion
anisotropy terms could properly describe the spin wave excitations, including
the newly observed low-lying energy excitation mode =0.45 meV
appearing at the magnetic zone centre. The spin wave dispersion and intensities
are highly sensitive to two differently aligned spin-canting sublattices in the
AF1 model. Thus this study reinsures the otherwise hardly provable hidden polar
character in MnWO.Comment: 7 pages, 5 figure
Andreev bound states versus Majorana bound states in quantum dot-nanowire-superconductor hybrid structures: Trivial versus topological zero-bias conductance peaks
Motivated by an important recent experiment [Deng et al., Science 354, 1557
(2016)], we theoretically consider the interplay between Andreev bound
states(ABSs) and Majorana bound states(MBSs) in quantum dot-nanowire
semiconductor systems with proximity-induced superconductivity(SC), spin-orbit
coupling and Zeeman splitting. The dot induces ABSs in the SC nanowire which
show complex behavior as a function of Zeeman splitting and chemical potential,
and the specific question is whether two such ABSs can come together forming a
topological MBS. We consider physical situations involving the dot being
non-SC, SC, or partially SC. We find that the ABSs indeed tend to coalesce
together producing near-zero-energy midgap states as Zeeman splitting and/or
chemical potential are increased, but this mostly happens in the
non-topological regime although there are situations where the ABSs could come
together forming a topological MBS. The two scenarios(two ABSs forming a
near-zero-energy non-topological ABS or a zero-energy topological MBS) are
difficult to distinguish by tunneling conductance spectroscopy due to
essentially the same signatures. Theoretically we distinguish them by knowing
the critical Zeeman splitting for the topological quantum phase transition or
by calculating the topological visibility. We find that the "sticking together"
propensity of ABSs to produce a zero-energy midgap state is generic in class D
systems, and by itself says nothing about the topological nature of the
underlying SC nanowire. One must use caution in interpreting tunneling
conductance measurements where the midgap sticking-together behavior of ABSs
cannot be construed as definitive evidence for topological SC with non-Abelian
MBSs. We also suggest some experimental techniques for distinguishing between
trivial and topological ZBCPs.Comment: 32 pages, 29 figure
A minimal two-band model for the superconducting Fe-pnictides
Following the discovery of the Fe-pnictide superconductors, LDA band
structure calculations showed that the dominant contributions to the spectral
weight near the Fermi energy came from the Fe 3d orbitals. The Fermi surface is
characterized by two hole surfaces around the point and two electron
surfaces around the M point of the 2 Fe/cell Brillouin zone. Here, we describe
a 2-band model that reproduces the topology of the LDA Fermi surface and
exhibits both ferromagnetic and spin density wave (SDW)
fluctuations. We argue that this minimal model contains the essential low
energy physics of these materials.Comment: 5 figures, 5 page
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