199 research outputs found
Quantum order by disorder in the Kitaev model on a triangular lattice
We identify and discuss the ground state of a quantum magnet on a triangular
lattice with bond-dependent Ising-type spin couplings, that is, a triangular
analog of the Kitaev honeycomb model. The classical ground-state manifold of
the model is spanned by decoupled Ising-type chains, and its accidental
degeneracy is due to the frustrated nature of the anisotropic spin couplings.
We show how this subextensive degeneracy is lifted by a quantum
order-by-disorder mechanism and study the quantum selection of the ground state
by treating short-wavelength fluctuations within the linked cluster expansion
and by using the complementary spin-wave theory. We find that quantum
fluctuations couple next-nearest-neighbor chains through an emergent four-spin
interaction, while nearest-neighbor chains remain decoupled. The remaining
discrete degeneracy of the ground state is shown to be protected by a hidden
symmetry of the model.Comment: 5 pages, 4 figure
Spin, Orbital and Charge Order at the Interface between Correlated Oxides
The collective behavior of correlated electrons in the VOinterface layer
of LaVO/SrTiO heterostructure is studied within a quarter-filled
-orbital Hubbard model on a square lattice. We argue that the ground
state is ferromagnetic driven by the double exchange mechanism, and is
orbitally and charge ordered due to a confined geometry and electron
correlations. The orbital and charge density waves open gaps on the entire
Fermi surfaces of all orbitals. The theory explains the observed insulating
behavior of the -type interface between LaVO and SrTiO.Comment: 4 pages, 5 figures; revised, to appear in Phys. Rev. Let
Renormalization group approach to the one-dimensional 1/4-filled Hubbard model with alternating on-site interactions
The one-dimensional Hubbard model with different on-site interactions is
investigated by renormalization group technique. In the case of a 1/4-filled
band the dynamical nonequivalence of sites leads to the appearance of Umklapp
processes in the system and to the dynamical generation of a gap in the charge
excitation spectrum for , or . The
ground-state phase diagram is obtained in the limit of second order
renormalization. Depending on the sign and relative values of the bare coupling
constants, there is a gap in the spin or charge excitation spectrum and the
model system tends to superconducting or antiferromagnetic order at T=0, with
doubled period. The role of interaction between particles on nearest and
next-nearest neighbor sites is also considered
Magnetically Hidden Order of Kramers Doublets in Systems: SrVO
We formulate and study an effective Hamiltonian for low-energy Kramers
doublets of -ions on a square lattice. We find that the system exhibits a
magnetically hidden order in which the expectation values of the local spin and
orbital moments both vanish. The order parameter responsible for a
time-reversal symmetry breaking has a composite nature and is a spin-orbital
analog of a magnetic octupole. We argue that such a hidden order is realized in
the layered perovskite SrVO.Comment: 4 pages, 3 figures; minor change
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