1,082 research outputs found
Integer filling metal insulator transitions in the degenerate Hubbard model
We obtain exact numerical solutions of the degenerate Hubbard model in the
limit of large dimensions (or large lattice connectivity). Successive
Mott-Hubbard metal insulator transitions at integer fillings occur at
intermediate values of the interaction and low enough temperature in the
paramagnetic phase. The results are relevant for transition metal oxides with
partially filled narrow degenerate bands.Comment: 4 pages + 4 figures (in 5 ps-files), revte
Mott transition in the Hubbard model away from particle-hole symmetry
We solve the Dynamical Mean Field Theory equations for the Hubbard model away
from the particle-hole symmetric case using the Density Matrix Renormalization
Group method. We focus our study on the region of strong interactions and
finite doping where two solutions coexist. We obtain precise predictions for
the boundaries of the coexistence region. In addition, we demonstrate the
capabilities of this precise method by obtaining the frequency dependent
optical conductivity spectra.Comment: 4 pages, 4 figures; updated versio
Electronic structure of CaSrVO: a tale of two energy-scales
We investigate the electronic structure of CaSrVO using
photoemission spectroscopy. Core level spectra establish an electronic phase
separation at the surface, leading to distinctly different surface electronic
structure compared to the bulk. Analysis of the photoemission spectra of this
system allowed us to separate the surface and bulk contributions. These results
help us to understand properties related to two vastly differing energy-scales,
namely the low energy-scale of thermal excitations (~) and the
high-energy scale related to Coulomb and other electronic interactions.Comment: 4 pages and 3 figures. Europhysics Letters (appearing
Serializing the Parallelism in Parallel Communicating Pushdown Automata Systems
We consider parallel communicating pushdown automata systems (PCPA) and
define a property called known communication for it. We use this property to
prove that the power of a variant of PCPA, called returning centralized
parallel communicating pushdown automata (RCPCPA), is equivalent to that of
multi-head pushdown automata. The above result presents a new sub-class of
returning parallel communicating pushdown automata systems (RPCPA) called
simple-RPCPA and we show that it can be written as a finite intersection of
multi-head pushdown automata systems
Quantum and thermal fluctuations in the SU(N) Heisenberg spin-glass model near the quantum critical point
We solve for the SU(N) Heisenberg spin-glass in the limit of large N focusing
on small S and T. We study the effect of quantum and thermal fluctuations in
the frequency dependent response function and observed interesting transfers of
spectral weight. We compute the T-dependence of the order parameter and the
specific heat and find an unusual T^2 behavior for the latter at low
temperatures in the spin-glass phase. We find a remarkable qualitative
agreement with various experiments on the quantum frustrated magnet
SrCr_{9p}Ga_{12-9p}O_{19}.Comment: 5 pages, 4 figures, submitted to Phys. Rev. Let
Propagating chain-free normal forms for EOL systems
We establish two types of normal forms for EOL systems. We first show that each ε-free EOL language can be generated by a propagating EOL system in which each derivation tree is chain-free. By this we mean that it contains at least one path from the root to the grandfather of a leaf in which each node has more than one son. We use this result to prove that each ε-free EOL language can be generated by a propagating EOL system in which each production has a right side of length at most two and which does not contain nonterminal chainproductions, i.e., productions A → B for nonterminals A and B. As applications of our results we give a simple proof for the decidability of the finiteness problem for EOL systems and solve an open problem concerning completeness of EOL forms
Non-equilibrium electronic transport in a one-dimensional Mott insulator
We calculate the non-equilibrium electronic transport properties of a
one-dimensional interacting chain at half filling, coupled to non-interacting
leads. The interacting chain is initially in a Mott insulator state that is
driven out of equilibrium by applying a strong bias voltage between the leads.
For bias voltages above a certain threshold we observe the breakdown of the
Mott insulator state and the establishment of a steady-state electronic current
through the system. Based on extensive time-dependent density matrix
renormalization group simulations, we show that this steady-state current
always has the same functional dependence on voltage, independent of the
microscopic details of the model and relate the value of the threshold to the
Lieb-Wu gap. We frame our results in terms of the Landau-Zener dielectric
breakdown picture. Finally, we also discuss the real-time evolution of the
current, and characterize the current-carrying state resulting from the
breakdown of the Mott insulator by computing the double occupancy, the spin
structure factor, and the entanglement entropy.Comment: 12 pages RevTex4, 12 eps figures, as published, minor revision
Magnetic Transition Temperature of (La,Sr)MnO
Using the Kondo lattice model with classical spins in infinite dimension,
magnetic phase transition in the perovskite-type transition-metal oxide
(La,Sr)MnO is theoretically studied. On the Bethe lattice, the
self-consistency equations are solved exactly. Curie temperatures at the region
of double-exchange ferromagnetism as well as the Neel
temperature at are well reproduced quantitatively. Pressure effect on the
Curie temperature is also discussed.Comment: 7 pages, 1 PS file with 3 figures appended at the end, LaTe
On insertion-deletion systems over relational words
We introduce a new notion of a relational word as a finite totally ordered
set of positions endowed with three binary relations that describe which
positions are labeled by equal data, by unequal data and those having an
undefined relation between their labels. We define the operations of insertion
and deletion on relational words generalizing corresponding operations on
strings. We prove that the transitive and reflexive closure of these operations
has a decidable membership problem for the case of short insertion-deletion
rules (of size two/three and three/two). At the same time, we show that in the
general case such systems can produce a coding of any recursively enumerable
language leading to undecidabilty of reachability questions.Comment: 24 pages, 8 figure
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