1,192 research outputs found
Caught in the Crossfire: Indiana\u27s Parent Trigger Law\u27s Negative Impact of Teacher Tenure
Stability of correlated electronic systems under the influence of the electron-phonon interaction
We have used an exact diagonalization technique to study the stability of the
-Holstein and Hubbard-Holstein models under the influence of the
electron-phonon interaction. Previous results have been obtained using
frozen-phonon technique or introducing only a few dynamical phonon modes due to
the large Hilbert space. To check these results we have done exact
diagonalization in a small cluster (four sites) including all the phonon modes
allowed by symmetry. We compare our results with those obtained by using the
adiabatic approximation.Comment: 10 pages, 2 Postscript figure
Inhomogeneous superconducting phases in the frustrated Kondo-Heisenberg chain
We use bosonization and renormalization group methods to determine the ground
state phase diagram of a one-dimensional frustrated Kondo-Heisenberg system
consisting of a one-dimensional spin-1/2 Luttinger liquid coupled by a Kondo
exchange interaction to a frustrated quantum antiferromagnetic Heisenberg
chain, with a nearest-neighbor exchange coupling and a
next-nearest-neighbor (frustrating) exchange interaction . We analyze the
interplay of quantum frustration in the antiferromagnetic chain with the Kondo
exchange coupling with the Luttinger liquid. We discuss the structure of
the phase diagram of this system as a function of the ratios ,
and of the parameters of the Luttinger liquid. In particular we
discuss in detail the regimes in which a pair-density-wave state may be
realized and its relation with the spin correlations in the frustrated
antiferromagnetic chain.Comment: 16 pages, 1 figure, 39 references; v2 with a new paragraph. Published
versio
Relevance of nonadiabatic effects in TiOCl
We analyze the effect of the phonon dynamics on a recently proposed model for
the uniform-incommensurate transition seen in TiOX compounds. The study is
based on a recently developed formalism for nonadiabatic spin-Peierls systems
based on bosonization and a mean field RPA approximation for the interchain
coupling. To reproduce the measured low temperature spin gap, a spin-phonon
coupling quite bigger than the one predicted from an adiabatic approach is
required. This high value is compatible with the renormalization of the phonons
in the high temperature phase seen in inelastic x-ray experiments. Our theory
accounts for the temperature of the incommensurate transition and the value of
the incommensurate wave vector at the transition point.Comment: 4 pages, 2 figure
Generation of chiral solitons in antiferromagnetic chains by a quantum quench
We analyze the time evolution of a magnetic excitation in a spin-1/2
antiferromagnetic Heisenberg chain after a quantum quench. By a proper
modulation of the magnetic exchange coupling, we prepare a static soliton of
total spin 1/2 as an initial spin state. Using bosonization and a numerical
time dependent density matrix renormalization group algorithm, we show that the
initial excitation evolves to a state composed of two counter-propagating
chiral states, which interfere to yield = 1/4 for each mode. We find that
these dynamically generated states remain considerably stable as time evolution
is carried out. We propose spin-Peierls materials and ultracold-atom systems as
suitable experimental scenarios in which to conduct and observe this mechanism.Comment: Published version. Title changed due to reinterpretation of results.
5 pages, 4 figure
Spectral gap induced by structural corrugation in armchair graphene nanoribbons
We study the effects of the structural corrugation or rippling on the
electronic properties of undoped armchair graphene nanoribbons (AGNR). First,
reanalyzing the single corrugated graphene layer we find that the two
inequivalent Dirac points (DP), move away one from the other. Otherwise, the
Fermi velocity decrease by increasing rippling. Regarding the AGNRs, whose
metallic behavior depends on their width, we analyze in particular the case of
the zero gap band-structure AGNRs. By solving the Dirac equation with the
adequate boundary condition we show that due to the shifting of the DP a gap
opens in the spectra. This gap scale with the square of the rate between the
high and the wavelength of the deformation. We confirm this prediction by exact
numerical solution of the finite width rippled AGNR. Moreover, we find that the
quantum conductance, calculated by the non equilibrium Green's function
technique vanish when the gap open. The main conclusion of our results is that
a conductance gap should appear for all undoped corrugated AGNR independent of
their width.Comment: 7 pages, 5 figure
- …