4,033 research outputs found
Bulk-interface correspondences for one dimensional topological materials with inversion symmetry
The interface between two materials described by spectrally gapped
Hamiltonians is expected to host an in-gap interface mode, whenever a certain
topological invariant changes across the interface. We provide a precise
statement of this bulk-interface correspondence, and its rigorous
justification. The correspondence applies to continuum and lattice models of
interfaces between one-dimensional materials with inversion symmetry, with
dislocation models being of particular interest. The relative Zak phase and
index theory are key aspects of our arguments.Comment: 33 pages, 2 figure
Ab initio study of the giant ferroelectric distortion and pressure induced spin-state transition in BiCoO3
Using configuration-state-constrained electronic structure calculations based
on the generalized gradient approximation plus Hubbard U method, we sought the
origin of the giant tetragonal ferroelectric distortion in the ambient phase of
the potentially multiferroic material BiCoO3 and identified the nature of the
pressure induced spin-state transition. Our results show that a strong Bi-O
covalency drives the giant ferroelectric distortion, which is further
stabilized by an xy-type orbital ordering of the high-spin (HS) Co3+ ions. For
the orthorhombic phase under 5.8 GPa, we find that a mixed HS and low-spin (LS)
state is more stable than both LS and intermediate-spin (IS) states, and that
the former well accounts for the available experimental results. Thus, we
identify that the pressure induced spin-state transition is via a mixed HS+LS
state, and we predict that the HS-to-LS transition would be complete upon a
large volume decrease of about 20%.Comment: 6 pages, 6 figures, 2 table
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