14,804 research outputs found
Engineering Quantum Spin Hall Effect in Graphene Nanoribbons via Edge Functionalization
Kane and Mele predicted that in presence of spin-orbit interaction graphene
realizes the quantum spin Hall state. However, exceptionally weak intrinsic
spin-orbit splitting in graphene ( eV) inhibits experimental
observation of this topological insulating phase. To circumvent this problem,
we propose a novel approach towards controlling spin-orbit interactions in
graphene by means of covalent functionalization of graphene edges with
functional groups containing heavy elements. Proof-of-concept first-principles
calculations show that very strong spin-orbit coupling can be induced in
realistic models of narrow graphene nanoribbons with tellurium-terminated
edges. We demonstrate that electronic bands with strong Rashba splitting as
well as the quantum spin Hall state spanning broad energy ranges can be
realized in such systems. Our work thus opens up new horizons towards
engineering topological electronic phases in nanostructures based on graphene
and other materials by means of locally introduced spin-orbit interactions.Comment: 5 pages, 3 figure
Existence of a multiplicative basis for a finitely spaced module over an aggregate
By [R. Bautista, P. Gabriel, A.V Roiter., L. Salmeron, Representation-finite
algebras and multiplicative basis. Invent. Math. 81 (1985) 217-285.], a
finite-dimensional algebra having finitely many isoclasses of indecomposable
representations admits a multiplicative basis. In Sections 4.10-4.12 of [P.
Gabriel, A. V. Roiter, Representations of finite-dimensional algebras.
Encyclopaedia of Math. Sci., vol. 73, Algebra 8, Springer-Verlag, 1992] an
analogous hypothesis was formulated for finitely spaced modules over an
aggregate. We prove this conjecture.Comment: 17 page
Structural insights into the membrane-extracted dimeric form of the ATPase TraB from the Escherichia coli pKM101 conjugation system
Background: Type IV secretion (T4S) systems are involved in secretion of virulence factors such as toxins or transforming molecules, or bacterial conjugation. T4S systems are composed of 12 proteins named VirB1-B11 and VirD4. Among them, three ATPases are involved in the assembly of the T4S system and/or provide energy for substrate transfer, VirB4, VirB11 and VirD4. The X-ray crystal structures of VirB11 and VirD4 have already been solved but VirB4 has proven to be reluctant to any structural investigation so far. Results: Here, we have used small-angle X-ray scattering to obtain the first structural models for the membrane-extracted, dimeric form of the TraB protein, the VirB4 homolog encoded by the E. coli pKM101 plasmid, and for the monomeric soluble form of the LvhB4 protein, the VirB4 homolog of the T4S system encoded by the Legionella pneumophila lvh operon. We have obtained the low resolution structures of the full-length TraB and of its N- and C-terminal halves. From these SAXS models, we derive the internal organisation of TraB. We also show that the two TraB N- and C-terminal domains are independently involved in the dimerisation of the full-length protein. Conclusions: These models provide the first structural insights into the architecture of VirB4 proteins. In particular, our results highlight the modular arrangement and functional relevance of the dimeric-membrane-bound form of TraB
Electronic properties of one-dimensional nanostructures of the BiSe topological insulator
We theoretically study the electronic structure and spin properties of
one-dimensional nanostructures of the prototypical bulk topological insulator
BiSe. Realistic models of experimentally observed BiSe
nanowires and nanoribbons are considered using the tight-binding method. At low
energies, the band structures are composed of a series of evenly spaced
degenerate sub-bands resulting from circumferential confinement of the
topological surface states. The direct band gaps due to the non-trivial
Berry phase show a clear dependence on the circumference. The spin-momentum
locking of the topological surface states results in a pronounced 2 spin
rotation around the circumference with the degree of spin polarization
dependent on the the momentum along the nanostructure. Overall, the band
structures and spin textures are more complicated for nanoribbons, which expose
two distinct facets. The effects of reduced dimensionality are rationalized
with the help of a simple model that considers circumferential quantization of
the topological surface states. Furthermore, the surface spin density induced
by electric current along the nanostructure shows a pronounced oscillatory
dependence on the charge-carrier energy, which can be exploited in spintronics
applications.Comment: 10 pages, 9 figure
Criticality and the Onset of Ordering in the Standard Vicsek Model
Experimental observations of animal collective behavior have shown stunning
evidence for the emergence of large-scale cooperative phenomena resembling
phase transitions in physical systems. Indeed, quantitative studies have found
scale-free correlations and critical behavior consistent with the occurrence of
continuous, second-order phase transitions. The Standard Vicsek Model (SVM), a
minimal model of self-propelled particles in which their tendency to align with
each other competes with perturbations controlled by a noise term, appears to
capture the essential ingredients of critical flocking phenomena. In this
paper, we review recent finite-size scaling and dynamical studies of the SVM,
which present a full characterization of the continuous phase transition
through dynamical and critical exponents. We also present a complex network
analysis of SVM flocks and discuss the onset of ordering in connection with
XY-like spin models.Comment: 15 pages, 4 figures. To appear in Interface Focu
Complex Network Structure of Flocks in the Standard Vicsek Model
In flocking models, the collective motion of self-driven individuals leads to
the formation of complex spatiotemporal patterns. The Standard Vicsek Model
(SVM) considers individuals that tend to adopt the direction of movement of
their neighbors under the influence of noise. By performing an extensive
complex network characterization of the structure of SVM flocks, we show that
flocks are highly clustered, assortative, and non-hierarchical networks with
short-tailed degree distributions. Moreover, we also find that the SVM dynamics
leads to the formation of complex structures with an effective dimension higher
than that of the space where the actual displacements take place. Furthermore,
we show that these structures are capable of sustaining mean-field-like
orientationally ordered states when the displacements are suppressed, thus
suggesting a linkage between the onset of order and the enhanced dimensionality
of SVM flocks.Comment: 26 pages, 11 figures. To appear in J. Stat. Phy
Macroscopic Observables Detecting Genuine Multipartite Entanglement and Partial Inseparability in Many-Body Systems
We show a general approach for detecting genuine multipartite entanglement
(GME) and partial inseparability in many-body-systems by means of macroscopic
observables (such as the energy) only. We show that the obtained criteria, the
"GME gap" and "the k-entanglement gap", detect large areas of genuine
multipartite entanglement and partial entanglement in typical many body states,
which are not detected by other criteria. As genuine multipartite entanglement
is a necessary property for several quantum information theoretic applications
such as e.g. secret sharing or certain kinds of quantum computation, our
methods can be used to select or design appropriate condensed matter systems.Comment: 4 pages, 3 figures, published version, title extende
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