78 research outputs found
Spin diffusion of the t-J model
The spin-diffusion constant of the 2D model is calculated for the first
time using an analytical approach at high temperatures and a recently-developed
numerical method based on the Lanczos technique combined with random sampling
in the intermediate temperature regime. A simple relation, ,
between spin conductivity and spin diffusion is established and used to
calculate the latter. In the high-temperature and low-doping limit the
calculated diffusion constant agrees with known results for the Heisenberg
model. At small hole doping, increases approximately linearly with
doping, which leads us to an important conclusion that hopping processes
enhance spin diffusion at high temperatures. At modest hole doping, , diffusion exhibits a nonmonotonic temperature dependence, which
indicates anomalous spin dynamics at small frequencies.Comment: 12 pages with figure
Productivity growth and functional upgrading in foreign subsidiaries in the Slovenian manufacturing sector
The paper discusses the determinants of productivity growth in manufacturing foreign subsidiaries in Slovenia. Special attention is given to the impact of control pattern. Using the standard growth accounting approach we show that productivity growth is significantly and positively correlated with the level of foreign parent companies' control of marketing and strategic business functions. Larger subsidiaries and subsidiaries with higher exports to sales ratio also experience higher changes in the productivity level. Subsidiaries in high technology intensity sectors exhibit significantly lower change in productivity than subsidiaries in other sectors
Anomalous Spin Dynamics in Doped Quantum Antiferromagnets
Finite-temperature spin dynamics in planar t-J model is studied using the
method based on the Lanczos diagonalization of small systems. Dynamical spin
structure factor at moderate dopings shows the coexistence of free-fermion-like
and spin-fluctuation timescales. At T<J, the low-frequency and static
susceptibility show pronounced T dependence, supporting a scenario, related to
the marginal Fermi-liquid one, for the explanation of neutron-scattering and
NMR-relaxation experiments in cuprates. Calculated NMR relaxation rates
reasonably reproduce experimental ones.Comment: 10 pages + 4 figures, Postscript in uuencoded compressed tar file,
IJS-TP-94/2
From local to nonlocal Fermi liquid in doped antiferromagnets
The variation of single-particle spectral functions with doping is studied
numerically within the t-J model. It is shown that corresponding self energies
change from local ones at the intermediate doping to strongly nonlocal ones for
a weakly doped antiferromagnet. The nonlocality shows up most clearly in the
pseudogap emerging in the density of states, due to the onset of short-range
antiferromagnetic correlations.Comment: 4 pages, 3 Postscript figures, revtex, submitted to Phys.Rev.Let
Korelacija između sadržaja titana u čeliku i elektromagnetskih svojstava neorijentiranih elektrolimova
In this study the correlation between the titanium content of steel and the core loss of non-oriented electrical steel sheets was determined. The core loss and titanium content of steel have a weak, but positive, correlation. The core loss was found to increase with an increasing titanium content. The study included a statistical analysis of an industrial data set and a metallographic analysis of the titanium inclusions. The analyzed titanium inclusions in the electrical steel sheets containing 0,006 mas.% Ti and 0,008 mas.% Ti were complex oxycarbonitrides, complex TiC and complex Ti(C,N).U radu se opisuje korelacija između sadržaja titana u čeliku i elektromagnetskih svojstava neorijentiranih elektrolimova. Postoji relativno niski stupanj pozitivne korelacije između magnetskih gubitaka i sadržajem titana. Magnetski gubici rastu sa sadržajem titana u čeliku. Izvedena je statistička analiza podataka za limove industrijske proizvodnje i metalografska analiza titanovih uključaka. Analizirani uključci u elektrolimovima sa 0,006 mas.% Ti i 0,008 mas.% Ti bili su kompleksni oksikarbonitridi, kompleksni TiC i kompleksni Ti(C,N)
Korelacija između sadržaja titana u čeliku i elektromagnetskih svojstava neorijentiranih elektrolimova
In this study the correlation between the titanium content of steel and the core loss of non-oriented electrical steel sheets was determined. The core loss and titanium content of steel have a weak, but positive, correlation. The core loss was found to increase with an increasing titanium content. The study included a statistical analysis of an industrial data set and a metallographic analysis of the titanium inclusions. The analyzed titanium inclusions in the electrical steel sheets containing 0,006 mas.% Ti and 0,008 mas.% Ti were complex oxycarbonitrides, complex TiC and complex Ti(C,N).U radu se opisuje korelacija između sadržaja titana u čeliku i elektromagnetskih svojstava neorijentiranih elektrolimova. Postoji relativno niski stupanj pozitivne korelacije između magnetskih gubitaka i sadržajem titana. Magnetski gubici rastu sa sadržajem titana u čeliku. Izvedena je statistička analiza podataka za limove industrijske proizvodnje i metalografska analiza titanovih uključaka. Analizirani uključci u elektrolimovima sa 0,006 mas.% Ti i 0,008 mas.% Ti bili su kompleksni oksikarbonitridi, kompleksni TiC i kompleksni Ti(C,N)
Magnetic properties of cuprate perovskites in the normal state
Normal-state magnetic properties of cuprate high-T_c superconductors are
interpreted based on the self-consistent solution of the t-J model of Cu-O
planes. The solution method retains the rotation symmetry of spin components in
the paramagnetic state and has no preset magnetic ordering. The obtained
solution is homogeneous. The calculated temperature and concentration
dependencies of the magnetic susceptibility are close to those observed in
experiment. These results offer explanations for the observed scaling of the
static uniform susceptibility and for the changes in the spin correlation
length, spin-lattice and spin-echo decay rates in terms of the temperature and
doping variations in the spin excitation spectrum.Comment: 9 pages, 5 figure
Temperature Dependence of Hall Response in Doped Antiferromagnets
Using finite-temperature Lanczos method the frequency-dependent Hall response
is calculated numerically for the t-J model on the square lattice and on
ladders. At low doping, both the high-frequency RH* and the d.c. Hall
coefficient RH0 follow qualitatively similar behavior at higher temperatures:
being hole-like for T > Ts~1.5J and weakly electron-like for T < Ts. Consistent
with experiments on cuprates, RH0 changes, in contrast to RH*, again to the
hole-like sign below the pseudogap temperature T*, revealing a strong
temperature variation for T->0.Comment: LaTeX, 4 pages, 4 figures, submitted to PR
Double exchange magnets: Spin-dynamics in the paramagnetic phase
The electronic structure of perovskite manganese oxides is investigated in
terms of a Kondo lattice model with ferromagnetic Hund coupling and
antiferromagnetic exchange between -spins using a finite temperature
diagonalization technique. Results for the dynamic structure factor are
consistent with recent neutron scattering experiments for the bilayer manganite
LaSrMnO . The susceptibility shows Curie-Weiss
behaviour and is used to derive a phase diagram. In the paramagnetic phase
carriers are characterized as ferromagnetic polarons in an antiferromagnetic
spin liquid.Comment: Revtex, 4 pages with 5 postscript figures include
Orbital dynamics in ferromagnetic transition metal oxides
We consider a model of strongly correlated electrons interacting by
superexchange orbital interactions in the ferromagnetic phase of LaMnO. It
is found that the classical orbital order with alternating occupied
orbitals has a full rotational symmetry at orbital degeneracy, and the
excitation spectrum derived using the linear spin-wave theory is gapless. The
quantum (fluctuation) corrections to the order parameter and to the ground
state energy restore the cubic symmetry of the model. By applying a uniaxial
pressure orbital degeneracy is lifted in a tetragonal field and one finds an
orbital-flop phase with a gap in the excitation spectrum. In two dimensions the
classical order is more robust near the orbital degeneracy point and quantum
effects are suppressed. The orbital excitation spectra obtained using finite
temperature diagonalization of two-dimensional clusters consist of a
quasiparticle accompanied by satellite structures. The orbital waves found
within the linear spin-wave theory provide an excellent description of the
dominant pole of these spectra.Comment: 13 pages, 12 figures, to appear in Phys. Rev.
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