18,847 research outputs found
Mean-Field Approach to Charge, Orbital, and Spin Ordering in Manganites
We present a mean-field theory of charge, orbital, and spin ordering in
manganites at 50% and 0% dopings by considering Jahn-Teller interaction,
nearest-neighbor repulsion, and no single-site double occupancy. For spinless
fermions, we show that Jahn-Teller distortion and charge-orbital ordering occur
simultaneously. In our two-dimensional model at 50% doping, for small
nearest-neighbor repulsion the system is orbitally polarized while for larger
repulsion the system undergoes CE type ordering. As for the 0% doping case, the
ground state is orbitally antiferromagnetic. Upon including spin degree of
freedom, at both 50% and 0% dopings the ordering remains the same at small
antiferromagnetic coupling between adjacent core spins.Comment: 4 pages, 3 figure
States of Local Moment Induced by Nonmagnetic Impurities in Cuprate Superconductors
By using a model Hamiltonian with d-wave superconductivity and competing
antiferromagnetic (AF) orders, the local staggered magnetization distribution
due to nonmagnetic impurities in cuprate superconductors is investigated. From
this, the net magnetic moment induced by a single or double impurities can be
obtained. We show that the net moment induced by a single impurity corresponds
to a local spin with S_z=0, or 1/2 depending on the strength of the AF
interaction and the impurity scattering. When two impurities are placed at the
nearest neighboring sites, the net moment is always zero. For two unitary
impurities at the next nearest neighboring sites, and at sites separated by a
Cu-ion site, the induced net moment has S_z=0, or 1/2, or 1. The consequence of
these results on experiments will be discussed.Comment: 4 pages, 4 figure
Compressibility of Interacting Electrons in Bilayer Graphene
Using the renormalized-ring-diagram approximation, we study the
compressibility of the interacting electrons in bilayer graphene. The
compressibility is equivalent to the spin susceptibility apart from a constant
factor. The chemical potential and the compressibility of the electrons can be
significantly altered by an energy gap (tunable by external gate voltages)
between the valence and conduction bands. For zero gap and a typical finite gap
in the experiments, we show both systems are stable.Comment: 5 pages, 6 figure
Absence of broken inversion symmetry phase of electrons in bilayer graphene under charge density fluctuations
On a lattice model, we study the possibility of existence of gapped broken
inversion symmetry phase (GBISP) of electrons with long-range Coulomb
interaction in bilayer graphene using both self-consistent Hartree-Fock
approximation (SCHFA) and the renormalized-ring-diagram approximation (RRDA).
RRDA takes into account the charge-density fluctuations beyond the mean field.
While GBISP at low temperature and low carrier concentration is predicted by
SCHFA, we show here the state can be destroyed by the charge-density
fluctuations. We also present a numerical algorithm for calculating the
self-energy of electrons with the singular long-range Coulomb interaction on
the lattice model.Comment: 8 pages, 6 figure
- …