147 research outputs found
Critical properties of the Kitaev-Heisenberg model
We study critical properties of the Kitaev-Heisenberg model on the honeycomb
lattice at finite temperatures which might describe the physics of the quasi
two-dimensional compounds, NaIrO and LiIrO. The model undergoes
two phase transitions as a function of temperature. At low temperature, thermal
fluctuations induce magnetic long-range order by order-by-disorder mechanism.
Magnetically ordered state with the spontaneously broken symmetry
persists up to a certain critical temperature. We find that there is an
intermediate phase between the low-temperature ordered phase and the
high-temperature disordered phase. The finite-sized scaling analysis suggests
that the intermediate phase is a critical Kosterlitz-Thouless phase with
continuously variable exponents. We argue that the intermediate phase has been
actually observed above the low-temperature magnetically ordered phase in
NaIrO, and likely in LiIrO.Comment: 5 pages, 6 figure
Magnetism in parent Fe-chalcogenides: quantum fluctuations select a plaquette order
We analyze magnetic order in iron-chalcogenide FeTe -- the parent
compound of high-temperature superconductor FeTeSe. Neutron
scattering experiments show that magnetic order in this material contains
components with momentum and in
Fe-only Brillouin zone. The actual spin order depends on the interplay between
these two components. Previous works argued that spin order is a single-
state (either or ). Such an order breaks rotational symmetry
and order spins into a double diagonal stripe. We show that quantum
fluctuations actually select another order -- a double plaquette state with
equal weight of and components, which preserves symmetry but
breaks translational symmetry. We argue that the plaquette state is
consistent with recent neutron scattering experiments on FeTe.Comment: 8 pages, 3 figure
Quantum spin liquid in the semiclassical regime
Quantum spin liquids have been at the forefront of correlated electron
research ever since their original proposal in 1973, and the realization that
they belong to the broader class of intrinsic topological orders, along with
the fractional quantum Hall states. According to received wisdom, quantum spin
liquids can arise in frustrated magnets with low spin , where strong quantum
fluctuations act to destabilize conventional, magnetically ordered states. Here
we present a magnet that has a quantum spin liquid ground state already
in the semiclassical, large- limit. The state has both topological and
symmetry related ground state degeneracy, and two types of gaps, a `magnetic
flux' gap that scales linearly with and an `electric charge' gap that drops
exponentially in . The magnet is described by the spin- version of the
spin-1/2 Kitaev honeycomb model, which has been the subject of intense studies
in correlated electron systems with strong spin-orbit coupling, and in optical
lattice realizations with ultracold atoms. The results apply to both integer
and half-integer spins
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