254,714 research outputs found
Determinations of upper critical field in continuous Ginzburg-Landau model
Novel procedures to determine the upper critical field have been
proposed within a continuous Ginzburg-Landau model. Unlike conventional
methods, where is obtained through the determination of the smallest
eigenvalue of an appropriate eigen equation, the square of the magnetic field
is treated as eigenvalue problems so that the upper critical field can be
directly deduced. The calculated from the two procedures are
consistent with each other and in reasonably good agreement with existing
theories and experiments. The profile of the order parameter associated with
is found to be Gaussian-like, further validating the methodology
proposed. The convergences of the two procedures are also studied.Comment: Revtex4, 8 pages, 4 figures, references modified, figures and table
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Observation of Fermi-energy dependent unitary impurity resonances in a strong topological insulator Bi_2Se_3 with scanning tunneling spectroscopy
Scanning tunneling spectroscopic studies of Bi_2Se_3 epitaxial films on Si (111) substrates reveal highly localized unitary impurity resonances associated with non-magnetic quantum impurities. The strength of the resonances depends on the energy difference between the Fermi level (E_F) and the Dirac point (E_D) and diverges as E_F approaches E_D. The Dirac-cone surface state of the host recovers within ~ 2Å spatial distance from impurities, suggesting robust topological protection of the surface state of topological insulators against high-density impurities that preserve time reversal symmetry
Magnetic anisotropy and spin-spiral wave in V, Cr and Mn atomic chains on Cu(001) surface: First principles calculations
Recent ab intio studies of the magnetic properties of all 3d transition
metal(TM) freestanding atomic chains predicted that these nanowires could have
a giant magnetic anisotropy energy (MAE) and might support a spin-spiral
structure, thereby suggesting that these nanowires would have technological
applicationsin, e.g., high density magnetic data storages. In order to
investigate how the substrates may affect the magnetic properties of the
nanowires, here we systematically study the V, Cr and Mn linear atomic chains
on the Cu(001) surface based on the density functional theory with the
generalized gradient approximation. We find that V, Cr, and Mn linear chains on
the Cu(001) surface still have a stable or metastable ferromagnetic state.
However, the ferromagnetic state is unstable against formation of a
noncollinear spin-spiral structure in the Mn linear chains and also the V
linear chain on the atop sites on the Cu(001) surface, due to the frustrated
magnetic interactions in these systems. Nonetheless, the presence of the
Cu(001) substrate does destabilize the spin-spiral state already present in the
freestanding V linear chain and stabilizes the ferromagnetic state in the V
linear chain on the hollow sites on Cu(001). When spin-orbit coupling (SOC) is
included, the spin magnetic moments remain almost unchanged, due to the
weakness of SOC in 3d TM chains. Furthermore, both the orbital magnetic moments
and MAEs for the V, Cr and Mn are small, in comparison with both the
corresponding freestanding nanowires and also the Fe, Co and Ni linear chains
on the Cu (001) surface.Comment: Accepted for publication in J. Phys. D: Applied Physic
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