692 research outputs found
Generating Diophantine Sets by Virus Machines
Virus Machines are a computational paradigm inspired by
the manner in which viruses replicate and transmit from one host cell to
another. This paradigm provides non-deterministic sequential devices.
Non-restricted virus machines are unbounded virus machines, in the
sense that no restriction on the number of hosts, the number of instructions
and the number of viruses contained in any host along any computation
is placed on them. The computational completeness of these
machines has been obtained by simulating register machines. In this
paper, virus machines as set generating devices are considered. Then,
the universality of non-restricted virus machines is proved by showing
that they can compute all diophantine sets, which the MRDP theorem
proves that coincide with the recursively enumerable sets.Ministerio de EconomÃa y Competitividad TIN2012- 3743
The Finite Temperature Mott Transition in the Hubbard Model in Infinite Dimensions
We study the second order finite temperature Mott transition point in the
fully frustrated Hubbard model at half filling, within Dynamical Mean Field
Theory. Using quantum Monte Carlo simulations we show the existence of a finite
temperature second order critical point by explicitly demonstrating the
existence of a divergent susceptibility as well as by finding coexistence in
the low temperature phase. We determine the location of the finite temperature
Mott critical point in the (U,T) plane. Our study verifies and quantifies a
scenario for the Mott transition proposed in earlier studies (Reviews of Modern
Physics 68, 13, 1996) of this problem.Comment: 4 RevTex pages, uses epsf, 2 figure
A mechanism for unipolar resistance switching in oxide non-volatile memory devices
Building on a recently introduced model for non-volatile resistive switching,
we propose a mechanism for unipolar resistance switching in
metal-insulator-metal sandwich structures. The commutation from the high to low
resistance state and back can be achieved with successive voltage sweeps of the
same polarity. Electronic correlation effects at the metal-insulator interface
are found to play a key role to produce a resistive commutation effect in
qualitative agreement with recent experimental reports on binary transition
metal oxide based sandwich structures.Comment: 4 pages, 2 figure
Landau Theory of the Finite Temperature Mott Transition
In the context of the dynamical mean-field theory of the Hubbard model, we
identify microscopically an order parameter for the finite temperature Mott
endpoint. We derive a Landau functional of the order parameter. We then use the
order parameter theory to elucidate the singular behavior of various physical
quantities which are experimentally accessible.Comment: 4 pages, 2 figure
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
Band-width control in a perovskite-type 3d^1 correlated metal Ca_1-xSr_xVO_3. II. Optical spectroscopy investigation
Optical conductivity spectra of single crystals of Ca_1-xSr_xVO_3 have been
studied to elucidate how the electronic behavior depends on the strength of the
electron correlation without changing the nominal number of electrons per
vanadium atom. The effective mass deduced by the analysis of the Drude-like
contribution do not show critical enhancement, even though the system is close
to the Mott transition. Besides the Drude-like contribution, two anomalous
features were observed in the optical conductivity spectra of the intraband
transition within the 3d band. These features can be assigned to transitions
involving the incoherent and coherent bands near the Fermi level. The large
spectral weight redistribution in this system, however, does not involve a
large mass enhancement.Comment: 12 pages in a Phys. Rev. B camera-ready format with 16 EPS figures
embedded. LaTeX 2.09 source file using "camera.sty" and "prbplug.sty"
provided by N. Shirakawa. For OzTeX (Macintosh), use "ozfig.sty" instead of
"psfig.sty". "ozfig.sty" can be also obtained by e-mail request to N.
Shirakawa: . Submitted to Phys. Rev. B. See "Part I (by
Inoue et al.)" at cond-mat/980107
Mott transition at large orbital degeneracy: dynamical mean-field theory
We study analytically the Mott transition of the N-orbital Hubbard model
using dynamical mean-field theory and a low-energy projection onto an effective
Kondo model. It is demonstrated that the critical interaction at which the
insulator appears (Uc1) and the one at which the metal becomes unstable (Uc2)
have different dependence on the number of orbitals as the latter becomes
large: Uc1 ~ \sqrt{N} while Uc2 ~ N. An exact analytical determination of the
critical coupling Uc2/N is obtained in the large-N limit. The metallic solution
close to this critical coupling has many similarities at low-energy with the
results of slave boson approximations, to which a comparison is made. We also
discuss how the critical temperature associated with the Mott critical endpoint
depends on the number of orbitals.Comment: 13 pages. Minor changes in V
Optical Conductivity in Mott-Hubbard Systems
We study the transfer of spectral weight in the optical spectra of a strongly
correlated electron system as a function of temperature and interaction
strength. Within a dynamical mean field theory of the Hubbard model that
becomes exact in the limit of large lattice coordination, we predict an
anomalous enhancement of spectral weight as a function of temperature in the
correlated metallic state and report on experimental measurements which agree
with this prediction in . We argue that the optical conductivity
anomalies in the metal are connected to the proximity to a crossover region in
the phase diagram of the model.Comment: 12 pages and 4 figures, to appear in Phys. Rev. Lett., v 75, p 105
(1995
- …