78,843 research outputs found
Topological Weyl and Node-Line Semimetals in Ferromagnetic Vanadium-Phosphorous-Oxide -VOPO Compound
We propose that the topological semimetal features can co-exist with
ferromagnetic ground state in vanadium-phosphorous-oxide -VOPO
compound from first-principles calculations. In this magnetic system with
inversion symmetry, the direction of magnetization is able to manipulate the
symmetric protected band structures from a node-line type to a Weyl one in the
presence of spin-orbital-coupling. The node-line semimetal phase is protected
by the mirror symmetry with the reflection-invariant plane perpendicular to
magnetic order. Within mirror symmetry breaking due to the magnetization along
other directions, the gapless node-line loop will degenerate to only one pair
of Weyl points protected by the rotational symmetry along the magnetic axis,
which are largely separated in momentum space. Such Weyl semimetal phase
provides a nice candidate with the minimum number of Weyl points in a condensed
matter system. The results of surface band calculations confirm the non-trivial
topology of this proposed compound. This findings provide a realistic candidate
for the investigation of topological semimetals with time-reversal symmetry
breaking, particularly towards the realization of quantum anomalous Hall effect
in Weyl semimetals.Comment: 5 pages, 4 figure
General response theory of topologically stable Fermi points and its implications for disordered cases
We develop a general response theory of gapless Fermi points with nontrivial
topological charges for gauge and nonlinear sigma fields, which asserts that
the topological character of the Fermi points is embodied as the terms with
discrete coefficients proportional to the corresponding topological charges.
Applying the theory to the effective non-linear sigma models for topological
Fermi points with disorders in the framework of replica approach, we derive
rigorously the Wess-Zumino terms with the topological charges being their
levels in the two complex symmetry classes of A and AIII. Intriguingly, two
nontrivial examples of quadratic Fermi points with the topological charge `2'
are respectively illustrated for the classes A and AIII. We also address a
qualitative connection of topological charges of Fermi points in the real
symmetry classes to the topological terms in the non-linear sigma models, based
on the one-to-one classification correspondence.Comment: 8 pages and 2 figures, revised version with appendi
Topological Classification and Stability of Fermi Surfaces
In the framework of the Cartan classification of Hamiltonians, a kind of
topological classification of Fermi surfaces is established in terms of
topological charges. The topological charge of a Fermi surface depends on its
codimension and the class to which its Hamiltonian belongs. It is revealed that
six types of topological charges exist, and they form two groups with respect
to the chiral symmetry, with each group consisting of one original charge and
two descendants. It is these nontrivial topological charges which lead to the
robust topological protection of the corresponding Fermi surfaces against
perturbations that preserve discrete symmetries.Comment: 5 pages, published version in PR
Revealing a topological connection between stabilities of Fermi surfaces and topological insulators/superconductors
A topology-intrinsic connection between the stabilities of Fermi surfaces
(FSs) and topological insulators/superconductors (TIs/TSCs) is revealed. In
particular, a one-to-one relation between the topological types of FSs and
TIs/TSCs is rigorously derived; combining it with a well-established
topological theory of FSs, we produce a complete table illustrating precisely
topological types of all TIs/TSCs, while a valid part of it was postulated
before. Moreover, we propose and prove a general index theorem that relates the
topological charge of FSs on the natural boundary of a strong TI/TSC to its
bulk topological number. Implications of the general index theorem on the
boundary quasi-particles are also addressed.Comment: 5 pages with Supplemental Material, more content is adde
Obvious enhancement of the total reaction cross sections for P with Si target and the possible relavent mechanisms
The reaction cross sections of P and the corresponding isotones on
Si target were measured at intermediate energies. The measured reaction cross
sections of the N=12 and 13 isotones show an abrupt increase at . The
experimental results for the isotones with as well as P can
be well described by the modified Glauber theory of the optical limit approach.
The enhancement of the reaction cross section for P could be explained
in the modified Glauber theory with an enlarged core. Theoretical analysis with
the modified Glauber theory of the optical limit and few-body approaches
underpredicted the experimental data of P. Our theoretical analysis
shows that an enlarged core together with proton halo are probably the
mechanism responsible for the enhancement of the cross sections for the
reaction of P+Si.Comment: 16 pages, 5 figures, to be published in Phys.Rev.
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