113 research outputs found
Topological Insulator in an Atomic Liquid
We demonstrate theoretically an atomic liquid phase that supports
topologically nontrivial electronic structure. A minimum two-orbital model of
liquid topological insulator in two dimensions is constructed within the
framework of tight-binding molecular dynamics. As temperature approaches zero,
our simulations show that the atoms crystallize into a triangular lattice with
nontrivial band topology at high densities. Thermal fluctuations at finite
temperatures melt the lattice, giving rise to a liquid state which inherits the
nontrivial topology from the crystalline phase. The electronic structure of the
resultant atomic liquid is characterized by a nonzero Bott index. Our work
broadens the notion of topological materials, and points to a new systematic
approach for searching topological phases in amorphous and liquid systems.Comment: 5 pages, 4 figure
Noncoplanar magnetic ordering driven by itinerant electrons on the pyrochlore lattice
Exchange interaction tends to favor collinear or coplanar magnetic orders in
rotationally invariant spin systems. Indeed, such magnetic structures are
usually selected by thermal or quantum fluctuations in highly frustrated
magnets. Here we show that a complex noncoplanar magnetic order with a
quadrupled unit cell is stabilized by itinerant electrons on the pyrochlore
lattice. Specifically we consider the Kondo-lattice and Hubbard models at
quarter filling. The electron Fermi 'surface' at this filling factor is
topologically equivalent to three intersecting Fermi circles. Perfect nesting
of the Fermi lines leads to magnetic ordering with multiple wavevectors and a
definite handedness. The chiral order might persist without magnetic order in a
chiral spin liquid at finite temperatures.Comment: 5 pages, 4 figure
Dipolar order by disorder in the classical Heisenberg antiferromagnet on the kagome lattice
Ever since the experiments which founded the field of highly frustrated
magnetism, the kagome Heisenberg antiferromagnet has been the archetypical
setting for the study of fluctuation induced exotic ordering. To this day the
nature of its classical low-temperature state has remained a mystery: the
non-linear nature of the fluctuations around the exponentially numerous
harmonically degenerate ground states has not permitted a controlled theory,
while its complex energy landscape has precluded numerical simulations at low
temperature. Here we present an efficient Monte Carlo algorithm which removes
the latter obstacle. Our simulations detect a low-temperature regime in which
correlations saturate at a remarkably small value. Feeding these results into
an effective model and analyzing the results in the framework of an appropriate
field theory implies the presence of long-range dipolar spin order with a
tripled unit cell.Comment: 5 pages, 4 figure
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