88,777 research outputs found
The valence band energy spectrum of HgTe quantum wells with inverted band structures
The energy spectrum of the valence band in HgTe/CdHgTe quantum
wells with a width ~nm has been studied experimentally by
magnetotransport effects and theoretically in framework -bands -method.
Comparison of the Hall density with the density found from period of the
Shubnikov-de Haas (SdH) oscillations clearly shows that the degeneracy of
states of the top of the valence band is equal to 2 at the hole density ~cm. Such degeneracy does not agree with the
calculations of the spectrum performed within the framework of the -bands
-method for symmetric quantum wells. These calculations show that the top
of the valence band consists of four spin-degenerate extremes located at (valleys) which gives the total degeneracy . It is shown that taking
into account the "mixing of states" at the interfaces leads to the removal of
the spin degeneracy that reduces the degeneracy to . Accounting for any
additional asymmetry, for example, due to the difference in the mixing
parameters at the interfaces, the different broadening of the boundaries of the
well, etc, leads to reduction of the valleys degeneracy, making . It is
noteworthy that for our case two-fold degeneracy occurs due to degeneracy of
two single-spin valleys. The hole effective mass () determined from
analysis of the temperature dependence of the amplitude of the SdH oscillations
show that is equal to and weakly increases with the
hole density. Such a value of and its dependence on the hole density are
in a good agreement with the calculated effective mass.Comment: 8 pages, 11 figure
High-Performance Solvers for Dense Hermitian Eigenproblems
We introduce a new collection of solvers - subsequently called EleMRRR - for
large-scale dense Hermitian eigenproblems. EleMRRR solves various types of
problems: generalized, standard, and tridiagonal eigenproblems. Among these,
the last is of particular importance as it is a solver on its own right, as
well as the computational kernel for the first two; we present a fast and
scalable tridiagonal solver based on the Algorithm of Multiple Relatively
Robust Representations - referred to as PMRRR. Like the other EleMRRR solvers,
PMRRR is part of the freely available Elemental library, and is designed to
fully support both message-passing (MPI) and multithreading parallelism (SMP).
As a result, the solvers can equally be used in pure MPI or in hybrid MPI-SMP
fashion. We conducted a thorough performance study of EleMRRR and ScaLAPACK's
solvers on two supercomputers. Such a study, performed with up to 8,192 cores,
provides precise guidelines to assemble the fastest solver within the ScaLAPACK
framework; it also indicates that EleMRRR outperforms even the fastest solvers
built from ScaLAPACK's components
Six-dimensional Davidson potential as a dynamical symmetry of the symplectic Interacting Vector Boson Model
A six-dimensional Davidson potential, introduced within the framework of the
Interacting Vector Boson Model (IVBM), is used to describe nuclei that exhibit
transitional spectra between the purely rotational and vibrational limits of
the theory. The results are shown to relate to a new dynamical symmetry that
starts with the reduction. Exact
solutions for the eigenstates of the model Hamiltonian in the basis defined by
a convenient subgroup chain of SO(6) are obtained. A comparison of the
theoretical results with experimental data for heavy nuclei with transitional
spectra illustrates the applicability of the theory.Comment: 9 pages, 4 figure
Modification of triaxial deformation and change of spectrum in $^{25}_{\ \Lambda}\Lambda$ hyperon
The positive-parity states of Mg with a hyperon
in orbit were studied with the antisymmetrized molecular dynamics for
hypernuclei. We discuss two bands of Mg corresponding to the
and bands of Mg. It is found that the energy of the
band is shifted up by about 200 keV compared to
Mg. This is because the hyperon in orbit reduces the
quadrupole deformation of the band, while it
does not change the deformation of the band
significantly.Comment: 19 pages, 3 figure
Coupling angle resolved photoemission data and quasiparticle structure in antiferromagnetic insulators Sr2CuO2Cl2 and Ca2CuO2Cl2
We have analyzed the quasiparticle dispersion and ARPES-spectral density for
Sr2CuO2Cl2 and Ca2CuO2Cl2 antiferromagnetic insulators along basic symmetric
directions of the Brillouin zone (BZ) in a framework of an extended tight
binding method (ETBM) with explicit account for intracell strong electron
correlations. The quasiparticle dispersion is in a good agreement with ARPES-
data. At the top of valence band we found a narrow impurity-like virtual level
with the spectral weight proportional to the concentration of spin
fluctuations. A pseudogap between the virtual level and the top of the valence
band has dispersion similar to 'remnant Fermi surface' in Ca2CuO2Cl2 and to a
pseudogap in the underdoped Bi2212 samples. A calculated parity of the
polarized ARPES-spectra in (0,0),(pi/2,pi/2),(pi,0) - points in the AFM- phase
is even with regard to relative magnitudes of the partial contributions by
different orbitals to the total ARPES- spectral density. Conditions of an
observability for the different partial contributions in the polarized ARPES-
experiments are determined also.Comment: 15 pdf-pages with 10 figures and tabl
Relaxed micromorphic model of transient wave propagation in anisotropic band-gap metastructures
In this paper, we show that the transient waveforms arising from several
localised pulses in a micro-structured material can be reproduced by a
corresponding generalised continuum of the relaxed micromorphic type.
Specifically, we compare the dynamic response of a bounded micro-structured
material to that of bounded continua with special kinematic properties: (i) the
relaxed micromorphic continuum and (ii) an equivalent Cauchy linear elastic
continuum. We show that, while the Cauchy theory is able to describe the
overall behaviour of the metastructure only at low frequencies, the relaxed
micromorphic model goes far beyond by giving a correct description of the pulse
propagation in the frequency band-gap and at frequencies intersecting the
optical branches. In addition, we observe a computational time reduction
associated with the use of the relaxed micromorphic continuum, compared to the
sensible computational time needed to perform a transient computation in a
micro-structured domain
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