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Filling dependence of a new type of charge ordered liquid on a triangular lattice system
We study the recently reported characteristic gapless charge ordered state in
a spinless fermion system on a triangular lattice under strong inter-site
Coulomb interactions. In this state the charges are spontaneously divided into
solid and liquid component, and the former solid part aligns in a Wigner
crystal manner while the latter moves among them like a pinball. We show that
such charge ordered liquid is stable over a wide range of filling, ,
and examine its filling dependent nature.Comment: 3 pages 3 figure
Carrier States and Ferromagnetism in Diluted Magnetic Semiconductors
Applying the dynamical coherent potential approximation to a simple model, we
have systematically studied the carrier states in Mn-type diluted
magnetic semiconductors (DMS's). The model calculation was performed for three
typical cases of DMS's: The cases with strong and moderate exchange
interactions in the absence of nonmagnetic potentials, and the case with strong
attractive nonmagnetic potentials in addition to moderate exchange interaction.
When the exchange interaction is sufficiently strong, magnetic impurity bands
split from the host band. Carriers in the magnetic impurity band mainly stay at
magnetic sites, and coupling between the carrier spin and the localized spin is
very strong. The hopping of the carriers among the magnetic sites causes
ferromagnetism through a {\it double-exchange (DE)-like} mechanism. We have
investigated the condition for the DE-like mechanism to operate in DMS's. The
result reveals that the nonmagnetic attractive potential at the magnetic site
assists the formation of the magnetic impurity band and makes the DE-like
mechanism operative by substantially enhancing the effect of the exchange
interaction. Using conventional parameters we have studied the carrier states
in GaMnAs. The result shows that the ferromagnetism is caused
through the DE-like mechanism by the carriers in the bandtail originating from
the impurity states.Comment: 20 pages, 14 figure
Tunneling splitting of magnetic levels in Fe8 detected by 1H NMR cross relaxation
Measurements of proton NMR and the spin lattice relaxation rate 1/T1 in the
octanuclear iron (III) cluster [Fe8(N3C6H15)6O2(OH)12][Br8 9H2O], in short Fe8,
have been performed at 1.5 K in a powder sample aligned along the main
anisotropy z axis, as a function of a transverse magnetic field (i.e.,
perpendicular to the main easy axis z). A big enhancement of 1/T1 is observed
over a wide range of fields (2.5-5 T), which can be attributed to the tunneling
dynamics; in fact, when the tunneling splitting of the pairwise degenerate
m=+-10 states of the Fe8 molecule becomes equal to the proton Larmor frequency
a very effective spin lattice relaxation channel for the nuclei is opened. The
experimental results are explained satisfactorily by considering the
distribution of tunneling splitting resulting from the distribution of the
angles in the hard xy plane for the aligned powder, and the results of the
direct diagonalization of the model Hamiltonian.Comment: J. Appl. Phys., in pres
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