3,301 research outputs found
A band structure scenario for the giant spin-orbit splitting observed at the Bi/Si(111) interface
The Bi/Si(111) (sqrt{3} x sqrt{3})R30 trimer phase offers a prime example of
a giant spin-orbit splitting of the electronic states at the interface with a
semiconducting substrate. We have performed a detailed angle-resolved
photoemission (ARPES) study to clarify the complex topology of the hybrid
interface bands. The analysis of the ARPES data, guided by a model
tight-binding calculation, reveals a previously unexplored mechanism at the
origin of the giant spin-orbit splitting, which relies primarily on the
underlying band structure. We anticipate that other similar interfaces
characterized by trimer structures could also exhibit a large effect.Comment: 11 pages, 13 figure
Local rectification of heat flux
We present a chain-of-atoms model where heat is rectified, with different
fluxes from the hot to the cold baths located at the chain boundaries when the
temperature bias is reversed. The chain is homogeneous except for boundary
effects and a local modification of the interactions at one site, the
"impurity". The rectification mechanism is due here to the localized impurity,
the only asymmetrical element of the structure, apart from the externally
imposed temperature bias, and does not rely on putting in contact different
materials or other known mechanisms such as grading or long-range interactions.
The effect survives if all interaction forces are linear except the ones for
the impurity.Comment: 5 pages, 5 figure
Carbon burning in intermediate mass primordial stars
The evolution of a zero metallicity 9 M_s star is computed, analyzed and
compared with that of a solar metallicity star of identical ZAMS mass. Our
computations range from the main sequence until the formation of a massive
oxygen-neon white dwarf. Special attention has been payed to carbon burning in
conditions of partial degeneracy as well as to the subsequent thermally pulsing
Super-AGB phase. The latter develops in a fashion very similar to that of a
solar metallicity 9 M_s star, as a consequence of the significant enrichment in
metals of the stellar envelope that ensues due to the so-called third dredge-up
episode. The abundances in mass of the main isotopes in the final ONe core
resulting from the evolution are X(^{16}O) approx 0.59, X(^{20}Ne) approx 0.28
and X(^{24}Mg) approx 0.05. This core is surrounded by a 0.05 M_s buffer mainly
composed of carbon and oxygen, and on top of it a He envelope of mass 10^{-4}
M_sComment: 11 pages, 11 figures, accepted for publication in A&
Tunable spin-gaps in a quantum-confined geometry
We have studied the interplay of a giant spin-orbit splitting and of quantum
confinement in artificial Bi-Ag-Si trilayer structures. Angle-resolved
photoelectron spectroscopy (ARPES) reveals the formation of a complex
spin-dependent gap structure, which can be tuned by varying the thickness of
the Ag buffer layer. This provides a means to tailor the electronic structure
at the Fermi energy, with potential applications for silicon-compatible
spintronic devices
Substituting fields within the action: consistency issues and some applications
In field theory, as well as in mechanics, the substitution of some fields in
terms of other fields at the level of the action raises an issue of consistency
with respect to the equations of motion. We discuss this issue and give an
expression which neatly displays the difference between doing the substitution
at the level of the Lagrangian or at the level of the equations of motion. Both
operations do not commute in general. A very relevant exception is the case of
auxiliary variables, which are discussed in detail together with some of their
relevant applications. We discuss the conditions for the preservation of
symmetries - Noether as well as non-Noether - under the reduction of degrees of
freedom provided by the mechanism of substitution. We also examine how the
gauge fixing procedures fit in our framework and give simple examples on the
issue of consistency in this case.Comment: 17 page
Near-threshold high-order harmonic spectroscopy with aligned molecules
We study high-order harmonic generation in aligned molecules close to the
ionization threshold. Two distinct contributions to the harmonic signal are
observed, which show very different responses to molecular alignment and
ellipticity of the driving field. We perform a classical electron trajectory
analysis, taking into account the significant influence of the Coulomb
potential on the strong-field-driven electron dynamics. The two contributions
are related to primary ionization and excitation processes, offering a deeper
understanding of the origin of high harmonics near the ionization threshold.
This work shows that high harmonic spectroscopy can be extended to the
near-threshold spectral range, which is in general spectroscopically rich.Comment: 4 pages, 4 figure
Neutron Stars—Cooling and Transport
Observations of thermal radiation from neutron stars can potentially provide information about the states of supranuclear matter in the interiors of these stars with the aid of the theory of neutron-star thermal evolution. We review the basics of this theory for isolated neutron stars with strong magnetic fields, including most relevant thermodynamic and kinetic properties in the stellar core, crust, and blanketing envelopes.The work of A.P. on the effects of strong magnetic fields on blanketing envelopes (Sect. 5.2 and Appendix B) has been supported by the Russian Science Foundation (grant 14-12-00316)
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