86,588 research outputs found

### Spontaneous quantum Hall effect in quarter-doped Hubbard model on honeycomb lattice and its possible realization in quarter-doped graphene system

We show that as the result of the nesting property of the Fermi surface, the
quarter-doped Hubbard model on honeycomb lattice is unstable with respect to
the formation of a magnetic insulating state with nonzero spin chirality for
infinitesimally small strength of electron correlation. The insulating state is
found to be topological nontrivial and to have a quantized Hall conductance of
$\sigma_{xy}=\frac{e^{2}}{h}$. We find the Fermi surface nesting is robust for
arbitrary value of next-nearest-neighbor hopping integral. It is thus very
possible that the quarter-doped graphene system will realize such an exotic
ground state. We also show that the quarter-doped Hubbard model on honeycomb
lattice is in exact equivalence in the weak coupling limit with the 3/4-filled
Hubbard model on triangular lattice, in which similar effect is also observed.Comment: A proof of the exact equivalence between the quarter-doped Hubbard
model on honeycomb lattice and the 3/4-filled Hubbard model on triangular
lattice in the weak coupling limit is adde

### A continuous family of fully-frustrated Heisenberg model on the Kagome lattice

We find that the antiferromagnetic Heisenberg model on the Kagome lattice
with nearest neighboring exchange coupling(NN-KAFH) belongs to a continuous
family of fully-frustrated Heisenberg model on the Kagome lattice, which has no
preferred classical ordering pattern. The model within this family consists of
the first, second and the third neighboring exchange coupling $J_{1}$, $J_{2}$,
and $J_{3}$, with $J_{2}=J_{3}$. We find that when $-J_{1}\leq J_{2}=J_{3}\leq
0.2J_{1}$, the lowest band of $J(\mathbf{q})$, namely, the Fourier transform of
the exchange coupling, is totally non-dispersive. Exact diagonalization
calculation indicates that the ground state of the spin-$\frac{1}{2}$ NN-KAFH
is locally stable under the perturbation of $J_{2}$ and $J_{3}$ when and only
when $J_{2}=J_{3}$. Interestingly, we find that the same flat band physics is
also playing an important role in the RVB description of the spin liquid state
on the Kagome lattice. In particular, we show that the extensively studied
$U(1)$ Dirac spin liquid state on the Kagome lattice can actually be generated
from a continuous family of gauge inequivalent RVB mean field ansatz, which
host very different mean field spinon dispersion.Comment: 5 pages, 7 figures. A correction made on the localized Wannier
orbital of the flat band of the spinon mode

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