10,311 research outputs found
Proximity-induced topological phases in bilayer graphene
We study the band structure of phases induced by depositing bilayer graphene
on a transition metal dichalcogenide monolayer. Tight-binding and low-energy
effective Hamiltonian calculations show that it is possible to induce
topologically nontrivial phases that should exhibit spin Hall effect in these
systems. We classify bulk insulating phases through calculation of the Z
invariant, which unequivocally identifies the topology of the structure. The
study of these and similar hybrid systems under applied gate voltage opens the
possibility for tunable topological structures in real experimental systems.Comment: 4 pages, 4 figure
Topological phases of topological insulator thin films
We study the properties of a thin film of topological insulator material. We
treat the coupling between helical states at opposite surfaces of the film in
the properly-adapted tunneling approximation, and show that the tunneling
matrix element oscillates as function of both the film thickness and the
momentum in the plane of the film for BiSe and BiTe. As a
result, while the magnitude of the matrix element at the center of the surface
Brillouin Zone gives the gap in the energy spectrum, the sign of the matrix
element uniquely determines the topological properties of the film, as
demonstrated by explicitly computing the pseudospin textures and the Chern
number. We find a sequence of transitions between topological and
non-topological phases, separated by semimetallic states, as the film thickness
varies. In the topological phase the edge states of the film always exist but
only carry a spin current if the edge potentials break particle-hole symmetry.
The edge states decay very slowly away from the boundary in BiSe,
making BiTe, where this scale is shorter, a more promising
candidate for the observation of these states. Our results hold for
free-standing films as well as heterostructures with large-gap insulators
Proximity-Induced Superconductivity at Non-Helical Topological Insulator Interfaces
We study how non-helical spin textures at the boundary between a topological
insulator (TI) and a superconductor (SC) affect the proximity-induced
superconductivity of the TI interface state. We consider TIs coupled to both
spin-singlet and spin-triplet SCs, and show that for the spin-triplet parent
SCs the resulting order parameter induced onto the interface state sensitively
depends on the symmetries which are broken at the TI-SC boundary. For chiral
spin-triplet parent SCs, we find that nodal proximity-induced superconductivity
emerges when there is broken twofold rotational symmetry which forces the spins
of the non-helical topological states to tilt away from the interface plane. We
furthermore show that the Andreev conductance of lateral heterostructures
joining TI-vacuum and TI-SC interfaces yields experimental signatures of the
reduced symmetries of the interface states.Comment: 5 pages, 2 figure
Modulation of endoglin expression in islets of langerhans by VEGF reveals a novel regulator of islet endothelial cell function
BACKGROUND: Endoglin/CD105 is an auxiliary receptor for transforming growth factor-β with established roles in vascular remodelling. It has recently been shown that heterozygous endoglin deficiency in mice decreases insulin secretion in an animal model of obesity, highlighting a potential role for endoglin in the regulation of islet function. We have previously identified two different populations of endoglin expressing cells in human and mouse islets which are: (i) endothelial cells (ECs) and (ii) islet mesenchymal stromal cells. The contribution of islet EC endoglin expression to islet development and sensitivity to VEGF is unknown and is the focus of this study. RESULTS: In vitro culture of mouse islets with VEGF164 for 48 h increased endoglin mRNA levels above untreated controls but VEGF did not modulate VEGFR2, CD31 or CD34 mRNA expression or islet viability. Removal of EC-endoglin expression in vivo reduced islet EC area but had no apparent effect on islet size or architecture. CONCLUSION: EC-specific endoglin expression in islets is sensitive to VEGF and plays partial roles in driving islet vascular development, however such regulation appears to be distinct to mechanisms required to modulate islet viability and size
Inertial amplification of continuous structures: Large band gaps from small masses
Wave motion in a continuous elastic rod with a periodically attached
inertial-amplification mechanism is investigated. The mechanism has properties
similar to an "inerter" typically used in vehicle suspensions, however here it
is constructed and utilized in a manner that alters the intrinsic properties of
a continuous structure. The elastodynamic band structure of the hybrid
rod-mechanism structure yields band gaps that are exceedingly wide and deep
when compared to what can be obtained using standard local resonators, while
still being low in frequency. With this concept, a large band gap may be
realized with as much as twenty times less added mass compared to what is
needed in a standard local resonator configuration. The emerging inertially
enhanced continuous structure also exhibits unique qualitative features in its
dispersion curves. These include the existence of a characteristic double-peak
in the attenuation constant profile within gaps and the possibility of
coalescence of two neighbouring gaps creating a large contiguous gap.Comment: Manuscript is under review for journal publicatio
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