3,993 research outputs found
Spin Bose Glass Phase in Bilayer Quantum Hall Systems at
We develop an effective spin theory to describe magnetic properties of the
Quantum Hall bilayer systems. In the absence of disorder this theory
gives quantitative agreement with the results of microscopic Hartree-Fock
calculations, and for finite disorder it predicts the existence of a novel spin
Bose glass phase. The Bose glass is characterized by the presence of domains of
canted antiferromagnetic phase with zero average antiferromagnetic order and
short range mean antiferromagnetic correlations. It has infinite
antiferromagnetic transverse susceptibility, finite longitudinal spin
susceptibility and specific heat linear in temperature. Transition from the
canted antiferromagnet phase to the spin Bose glass phase is characterized by a
universal value of the longitudinal spin conductance.Comment: 4 pages, 4 eps figure
Magnetization in electron- and Mn- doped SrTiO3
Mn-doped SrTiO_3.0, when synthesized free of impurities, is a paramagnetic
insulator with interesting dielectric properties. Since delocalized charge
carriers are known to promote ferromagnetism in a large number of systems via
diverse mechanisms, we have looked for the possibility of any intrinsic,
spontaneous magnetization by simultaneous doping of Mn ions and electrons into
SrTiO_3 via oxygen vacancies, thereby forming SrTi_(1-x)Mn_xO_(3-d), to the
extent of making the doped system metallic. We find an absence of any
enhancement of the magnetization in the metallic sample when compared with a
similarly prepared Mn doped, however, insulating sample. Our results, thus, are
not in agreement with a recent observation of a weak ferromagnetism in metallic
Mn doped SrTiO_3 system.Comment: 10 pages and 4 figure
Resonant optical electron transfer in one-dimensional multiwell structures
We consider coherent single-electron dynamics in the one-dimensional
nanostructure under resonant electromagnetic pulse. The structure is composed
of two deep quantum wells positioned at the edges of structure and separated by
a sequence of shallow internal wells. We show that complete electron transfer
between the states localized in the edge wells through one of excited
delocalized states can take place at discrete set of times provided that the
pulse frequency matches one of resonant transition frequencies. The transfer
time varies from several tens to several hundreds of picoseconds and depends on
the structure and pulse parameters. The results obtained in this paper can be
applied to the developments of the quantum networks used in quantum
communications and/or quantum information processing.Comment: 25 pages,16 figure
Temperature dependent spin susceptibility in a two-dimensional metal
We consider a two-dimensional electron system with Coulomb interaction
between particles at a finite temperature T. We show that the dynamic Kohn
anomaly in the response function at 2K_F leads to a linear-in-T correction to
the spin susceptibility, same as in systems with short-range interaction.
We show that the singularity of the Coulomb interaction at q=0 does not
invalidate the expansion in powers of r_s, but makes the expansion
non-analytic. We argue that the linear temperature dependence is consistent
with the general structure of Landau theory and can be viewed as originating
from the non-analytic component of the Landau function near the Fermi surface.Comment: 4 pages, no figure
First-principles Calculations of the Electronic Structure and Spectra of Strongly Correlated Systems: Dynamical Mean-field Theory
A recently developed dynamical mean-field theory in the iterated perturbation
theory approximation was used as a basis for construction of the "first
principles" calculation scheme for investigating electronic structure of
strongly correlated electron systems. This scheme is based on Local Density
Approximation (LDA) in the framework of the Linearized Muffin-Tin-Orbitals
(LMTO) method. The classical example of the doped Mott-insulator
La_{1-x}Sr_xTiO_3 was studied by the new method and the results showed
qualitative improvement in agreement with experimental photoemission spectra.Comment: 11 pages, 3 Postscript figures, LaTeX, submit in Journal of Physics:
Condensed Matte
Ferromagnetic and random spin ordering in diluted magnetic semiconductors
In a diluted magnetic semiconductor system, the exchange interaction between
magnetic impurities has two independent components: a direct antiferromagnetic
interaction and a ferromagnetic interaction mediated by charge carriers.
Depending on the system parameters, the ground state of the system may be
ordered either ferromagnetically or randomly. In this paper we use percolation
theory to find the ferromagnetic transition temperature and the location of the
quantum critical point separating the ferromagnetic phase and a valence bond
glass phase.Comment: 9 pages, 2 figures, a reference adde
Probing -Spin Correlations in Optical Lattices
We propose a technique to measure multi-spin correlation functions of
arbitrary range as determined by the ground states of spinful cold atoms in
optical lattices. We show that an observation of the atomic version of the
Stokes parameters, using focused lasers and microwave pulsing, can be related
to -spin correlators. We discuss the possibility of detecting not only
ground state static spin correlations, but also time-dependent spin wave
dynamics as a demonstrative example using our proposed technique.Comment: 7 pages, 4 figure
Bilayer Quantum Hall Systems at Filling Factor \nu=2: An Exact Diagonalisation Study
We present an exact diagonalisation study of bilayer quantum Hall systems at
a filling factor of two in the spherical geometry. We find the
high-Zeeman-coupling phase boundary of the broken symmetry canted
antiferromagnet is given exactly by previous Hartree-Fock mean-field theories,
but that the state's stability at weak Zeeman coupling has been qualitatively
overestimated. In the absence of interlayer tunneling, degeneracies occur
between total spin multiplets due to the Hamiltonian's invariance under
independent spin-rotations in top and bottom two-dimensional electron layers.Comment: Some remarks added in the discussion of the phase diagram, and some
typos corrected. Version to be published in Phys. Rev. Let
Does Inner Awareness Always Accompany Outer Awareness During Perception?
In the present paper, we defend the thesis that outer-world-directed perceptual consciousness is always accompanied by an inner awareness (IAOA). This is contrary to the view that outer-world-directed conscious mental states are not accompanied by an inner awareness, which is held by Gennaro (2008) against Kriegel’s (2009a and 2009b) self-representationalism. We attempt to show why philosophers like Gennaro get it wrong when they deny the IAOA thesis by critically examining his arguments against it and by giving arguments in its favour.Ar vidinis žinojimas percepcijos metu visada lydi išorinį žinojimą
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