56 research outputs found
Nature of Possible Magnetic Phases in Frustrated Hyperkagome Iridate
Based on Kitaev-Heisenberg model with Dzyaloshinskii-Moriya (DM)
interactions, we studied nature of possible magnetic phases in frustrated
hyperkagome iridate, NaIrO (Na-438). Using Monte-Carlo
simulation, we showed that the phase diagram is mostly covered by two competing
magnetic ordered phases; Z symmetry breaking (SB) phase and Z SB phase,
latter of which is stabilized by the classical order by disorder. These two
phases are separated by a first order phase transition line with Z-like
symmetry. The critical nature at the Z SB ordering temperature is
characterized by the 3D XY universality class, below which U(1) to Z
crossover phenomena appears; the Z spin anisotropy becomes irrelevant in a
length scale shorter than a crossover length while becomes relevant
otherwise. A possible phenomenology of polycrystalline Na-438 is discussed
based on this crossover phenomena
Chiral Topological Excitons in a Chern Band Insulator
A family of semiconductors called as Chern band insulator are shown to host
exciton bands with non-zero topological Chern integers and chiral exciton edge
modes. Using a prototypical two-band Chern insulator model, we calculate a
cross-correlation function to obtain the exciton bands and their Chern
integers. The lowest exciton band acquires Chern integers such as and
in electronic Chern insulator phase. The non-trivial topology can be
experimentally observed both by non-local optoelectronic response of exciton
edge modes and by a phase shift in the cross-correlation response due to the
bulk mode. Our result suggests that magnetically doped HgTe, InAs/GaSb quantum
wells and thin film are promising candidates
for a platform of topological excitonics.Comment: 5+ pages, 3 figures with supplemental material
Magnetostatic wave analog of integer quantum Hall state in patterned magnetic films
A magnetostatic spin wave analog of integer quantum Hall (IQH) state is
proposed in realistic patterned ferromagnetic thin films. Due to magnetic shape
anisotropy, magnetic moments in a thin film lie within the plane, while all
spin-wave excitations are fully gapped. Under an out-of-plane magnetic field,
the film acquires a finite magnetization, where some of the gapped magnons
become significantly softened near a saturation field. It is shown that, owing
to a spin-orbit locking nature of the magnetic dipolar interaction, these soft
spin-wave volume-mode bands become chiral volume-mode bands with finite
topological Chern integers. A bulk-edge correspondence in IQH physics suggests
that such volume-mode bands are accompanied by a chiral magnetostatic spin-wave
edge mode. The existence of the edge mode is justified both by micromagnetic
simulations and by band calculations based on a linearized Landau-Lifshitz
equation. Employing intuitive physical arguments, we introduce proper
tight-binding models for these soft volume-mode bands. Based on the
tight-binding models, we further discuss possible applications to other systems
such as magnetic ultrathin films with perpendicular magnetic anisotropy (PMA).Comment: 20 pages, 12 figure
Quantum Multicriticality in Disordered Weyl Semimetal
In electronic band structure of solid state material, two band touching
points with linear dispersion appear in pair in the momentum space. When they
annihilate with each other, the system undergoes a quantum phase transition
from three-dimensional Weyl semimetal (WSM) phase to a band insulator phase
such as Chern band insulator (CI) phase. The phase transition is described by a
new critical theory with a `magnetic dipole' like object in the momentum space.
In this paper, we reveal that the critical theory hosts a novel disorder-driven
quantum multicritical point, which is encompassed by three quantum phases,
renormalized WSM phase, CI phase, and diffusive metal (DM) phase. Based on the
renormalization group argument, we first clarify scaling properties around the
band touching points at the quantum multicritical point as well as all phase
boundaries among these three phases. Based on numerical calculations of
localization length, density of states and critical conductance distribution,
we next prove that a localization-delocalization transition between the CI
phase with a finite zero-energy density of states (zDOS) and DM phase belongs
to an ordinary 3D unitary class. Meanwhile, a localization-delocalization
transition between the Chern insulator phase with zero zDOS and a renormalized
Weyl semimetal (WSM) phase turns out to be a direct phase transition whose
critical exponent . We interpret these numerical results by a
renormalization group analysis on the critical theory.Comment: 23 pages with 14 figures and 4 table
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