3,348 research outputs found
Bulk-boundary correspondence for three-dimensional symmetry-protected topological phases
We derive a bulk-boundary correspondence for three-dimensional (3D)
symmetry-protected topological (SPT) phases with unitary symmetries. The
correspondence consists of three equations that relate bulk properties of these
phases to properties of their gapped, symmetry-preserving surfaces. Both the
bulk and surface data appearing in our correspondence are defined via a
procedure in which we gauge the symmetries of the system of interest and then
study the braiding statistics of excitations of the resulting gauge theory. The
bulk data is defined in terms of the statistics of bulk excitations, while the
surface data is defined in terms of the statistics of surface excitations. An
appealing property of this data is that it is plausibly complete in the sense
that the bulk data uniquely distinguishes each 3D SPT phase, while the surface
data uniquely distinguishes each gapped, symmetric surface. Our correspondence
applies to any 3D bosonic SPT phase with finite Abelian unitary symmetry group.
It applies to any surface that (1) supports only Abelian anyons and (2) has the
property that the anyons are not permuted by the symmetries.Comment: 31 pages, 14 figures, 1 tabl
Development of sustainable esterification reactions and the transformation of carbohydrates into applicable building blocks
This thesis showcases some developments in chemical processes and synthesis leading to products of commercial interest. The thesis includes studies on esterification reactions to improve the catalysis of these reactions. In addition, deoxydehydration (DODH) reactions of alkyl glycosides are studied and illustrated. DODH reactions were performed to convert alkyl glycosides into diols, by eliminating a cis-diol moiety in pyranosides to result in alkenes and alkanes. Furthermore, this thesis presents the transformation of some common alkyl glycosides into their rare counterparts (C3-epimers) by sequential C3-oxidation and heterogeneous hydrogenation. Finally, the development of novel fructose-based surfactants from fructose and its derived saccharides is studied and discussed
Zero bias conductance peak in Majorana wires made of semiconductor-superconductor hybrid structures
Motivated by a recent experimental report[1] claiming the likely observation
of the Majorana mode in a semiconductor-superconductor hybrid
structure[2,3,4,5], we study theoretically the dependence of the zero bias
conductance peak associated with the zero-energy Majorana mode in the
topological superconducting phase as a function of temperature, tunnel barrier
potential, and a magnetic field tilted from the direction of the wire for
realistic wires of finite lengths. We find that higher temperatures and tunnel
barriers as well as a large magnetic field in the direction transverse to the
wire length could very strongly suppress the zero-bias conductance peak as
observed in Ref.[1]. We also show that a strong magnetic field along the wire
could eventually lead to the splitting of the zero bias peak into a doublet
with the doublet energy splitting oscillating as a function of increasing
magnetic field. Our results based on the standard theory of topological
superconductivity in a semiconductor hybrid structure in the presence of
proximity-induced superconductivity, spin-orbit coupling, and Zeeman splitting
show that the recently reported experimental data are generally consistent with
the existing theory that led to the predictions for the existence of the
Majorana modes in the semiconductor hybrid structures in spite of some apparent
anomalies in the experimental observations at first sight. We also make several
concrete new predictions for future observations regarding Majorana splitting
in finite wires used in the experiments.Comment: 5 pages, 6 figures: revised submitted versio
Systematic {\em ab initio} study of the phase diagram of epitaxially strained SrTiO
We use density-functional theory with the local-density approximation to
study the structural and ferroelectric properties of SrTiO under misfit
strains. Both the antiferrodistortive (AFD) and ferroelectric (FE)
instabilities are considered. The rotation of the oxygen octahedra and the
movement of the atoms are fully relaxed within the constraint of a fixed
in-plane lattice constant. We find a rich misfit strain-induced phase
transition sequence and is obtained only when the AFD distortion is taken into
account. We also find that compressive misfit strains induce ferroelectricity
in the tetragonal low temperature phase only whilst tensile strains induce
ferroelectricity in the orthorhombic phases only. The calculated FE
polarization for both the tetragonal and orthorhombic phases increases
monotonically with the magnitude of the strains. The AFD rotation angle of the
oxygen octahedra in the tetragonal phase increases dramatically as the misfit
strain goes from the tensile to compressive strain region whilst it decreases
slightly in the orthorhombic (FO4) phase. This reveals why the polarization in
the epitaxially strained SrTiO would be larger when the tensile strain is
applied, since the AFD distortion is found to reduce the FE instability and
even to completely suppress it in the small strain region. Finally, our
analysis of the average polar distortion and the charge density distribution
suggests that both the Ti-O and Sr-O layers contribute significantly to the FE
polarization
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