56 research outputs found
Entanglement, excitations and correlation effects in narrow zigzag graphene nanoribbons
We investigate the low-lying excitation spectrum and ground-state properties
of narrow graphene nanoribbons with zigzag edge configurations. Nanoribbons of
comparable widths have been synthesized very recently [P. Ruffieux, \emph{et
al.} Nature \textbf{531}, 489 (2016)], and their descriptions require more
sophisticated methods since in this regime conventional methods, like
mean-field or density-functional theory with local density approximation, fail
to capture the enhanced quantum fluctuations. Using the unbiased density-matrix
renormalization group algorithm we calculate the charge gaps with high accuracy
for different widths and interaction strengths and compare them with mean-field
results. It turns out that the gaps are much smaller in the former case due to
the proper treatment of quantum fluctuations. Applying the elements of quantum
information theory we also reveal the entanglement structure inside a ribbon
and examine the spectrum of subsystem density matrices to understand the origin
of entanglement. We examine the possibility of magnetic ordering and the effect
of magnetic field. Our findings are relevant for understanding the gap values
in different recent experiments and the deviations between them.Comment: 8 pages, 7 figures, revised version, accepted for publication in PR
Competition between Hund's coupling and Kondo effect in a one-dimensional extended periodic Anderson model
We study the ground-state properties of an extended periodic Anderson model
to understand the role of Hund's coupling between localized and itinerant
electrons using the density-matrix renormalization group algorithm. By
calculating the von Neumann entropies we show that two phase transitions occur
and two new phases appear as the hybridization is increased in the symmetric
half-filled case due to the competition between Kondo-effect and Hund's
coupling. In the intermediate phase, which is bounded by two critical points,
we found a dimerized ground state, while in the other spatially homogeneous
phases the ground state is Haldane-like and Kondo-singlet-like, respectively.
We also determine the entanglement spectrum and the entanglement diagram of the
system by calculating the mutual information thereby clarifying the structure
of each phase.Comment: 9 pages, 9 figures, revised version, accepted for publication in PR
Mott transition and dimerization in the one-dimensional SU Hubbard model
The one-dimensional SU Hubbard model is investigated numerically for
, and 5 at half filling and filling using the density-matrix
renormalization-group (DMRG) method. The energy gaps and various quantum
information entropies are calculated. In the half-filled case, finite spin and
charge gaps are found for arbitrary positive if . Furthermore, it is
shown that the transition to the gapped phase at is of
Kosterlitz-Thouless type and is accompanied by a bond dimerization both for
even and odd . In the -filled case, the transition has similar features
as the metal-insulator transition in the half-filled SU(2) Hubbard model. The
charge gap opens exponentially slowly for , the spin sector
remains gapless, and the ground state is non-dimerized.Comment: 9 pages, 12 figure
Spatially nonuniform phases in the one-dimensional SU(n) Hubbard model for commensurate fillings
The one-dimensional repulsive SU Hubbard model is investigated
analytically by bosonization approach and numerically using the density-matrix
renormalization-group (DMRG) method for , and 5 for commensurate
fillings where and are relatively prime. It is shown that the
behavior of the system is drastically different depending on whether ,
, or , the umklapp processes are irrelevant, the model is
equivalent to an -component Luttinger liquid with central charge . When
, the charge and spin modes are decoupled, the umklapp processes open a
charge gap for finite , whereas the spin modes remain gapless and the
central charge . The translational symmetry is not broken in the ground
state for any . On the other hand, when , the charge and spin modes are
coupled, the umklapp processes open gaps in all excitation branches, and a
spatially nonuniform ground state develops. Bond-ordered dimerized, trimerized
or tetramerized phases are found depending on the filling.Comment: 10 pages, 11 figure
Окремі проблеми визначення сутності адміністративної відповідальності у сфері використання природних ресурсів
Легеза Ю. О. Окремі проблеми визначення сутності адміністративної відповідальності у сфері використання природних ресурсів / Ю. О. Легеза // Традиції та новації юридичної науки: минуле, сучасність, майбутнє : матер. Міжнар. наук.-практ. конф. (м. Одеса, 19 трав. 2017 р.). У 2-х т. Т. 2 / відп. ред. Г. О. Ульянова. - Одеса : Видавничий дім "Гельветика", 2017. - С. 28-30
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