31,666 research outputs found
Topological phases in a two-dimensional lattice: Magnetic field versus spin-orbit coupling
In this work, we explore the rich variety of topological states that arise in
two-dimensional systems, by considering the competing effects of spin-orbit
couplings and a perpendicular magnetic field on a honeycomb lattice. Unlike
earlier approaches, we investigate minimal models in order to clarify the
effects of the intrinsic and Rashba spin-orbit couplings, and also of the
Zeeman splitting, on the quantum Hall states generated by the magnetic field.
In this sense, our work provides an interesting path connecting quantum Hall
and quantum spin Hall physics. First, we consider the properties of each term
individually and we analyze their similarities and differences. Secondly, we
investigate the subtle competitions that arise when these effects are combined.
We finally explore the various possible experimental realizations of our model.Comment: 19 pages, 15 figure
Ion-Solvent Interaction Studies of Chlorides, Bromides & Nitrates of Sodium & Potassium in Dioxane-Water Mixtures at Different Temperatures
826-82
Viscosity & Apparent Molal Volume of Potassium Chloride in Acetone-, Dioxane- & Methyl Alcohol-Water Mixtures
824-82
Mechanical property evaluation of an Al-2024 alloy subjected to HPT processing
An aluminum-copper alloy (Al-2024) was successfully subjected to high-pressure torsion (HPT) up to five turns at room temperature under an applied pressure of 6.0 GPa. The Al-2024 alloy is used as a fuselage structural material in the aerospace sector. Mechanical properties of the HPT-processed Al-2024 alloy were evaluated using the automated ball indentation technique. This test is based on multiple cycles of loading and unloading where a spherical indenter is used. After two and five turns of HPT, the Al-2024 alloy exhibited a UTS value of ~1014 MPa and ~1160 MPa respectively, at the edge of the samples. The microhardness was measured from edges to centers for all HPT samples. These results clearly demonstrate that processing by HPT gives a very significant increase in tensile properties and the microhardness values increase symmetrically from the centers to the edges. Following HPT, TEM examination of the five-turn HPT sample revealed the formation of high-angle grain boundaries and a large dislocation density with a reduced average grain size of ~80 nm. These results also demonstrate that high-pressure torsion is a processing tool for developing nanostructures in the Al-2024 alloy with enhanced mechanical propertie
Changes in the electronic structure and properties of graphene induced by molecular charge-transfer
Interaction with electron donor and acceptor molecules such as aniline and
nitrobenzene brings about marked changes in the Raman spectrum and the
electronic structure of graphene, prepared by the exfoliation of graphitic
oxide.Comment: 13 pages, 4 figure
Comparison of perturbative expansions using different phonon bases for two-site Holstein model
The two-site single-polaron problem is studied within the perturbative
expansions using different standard phonon basis obtained through the Lang
Firsov (LF), modified LF (MLF) and modified LF transformation with squeezed
phonon states (MLFS). The role of these convergent expansions using the above
prescriptions in lowering the energy and in determining the correlation
functions are compared for different values of coupling strength. The
single-electron energy, oscillator wave functions and correlation functions are
calculated for the same system. The applicability of different phonon basis in
different regimes of the coupling strength as well as in different regimes of
hopping are also discussed.Comment: 24 pages (RevTEX), 12 postscript figures, final version accepted in
PRB(2000) Jornal Ref: Phys. Rev. B, 61, 4592-4602 (2000
Temperature and magnetization-dependent band-gap renormalization and optical many-body effects in diluted magnetic semiconductors
We calculate the Coulomb interaction induced density, temperature and
magnetization dependent many-body band-gap renormalization in a typical diluted
magnetic semiconductor GaMnAs in the optimally-doped metallic regime as a
function of carrier density and temperature. We find a large (about 0.1 eV)
band gap renormalization which is enhanced by the ferromagnetic transition. We
also calculate the impurity scattering effect on the gap narrowing. We suggest
that the temperature, magnetization, and density dependent band gap
renormalization could be used as an experimental probe to determine the valence
band or the impurity band nature of carrier ferromagnetism.Comment: Revised versio
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