Nature Communications,
Journal Year:
2020,
Volume and Issue:
11(1)
Published: July 28, 2020
Abstract
The
quantum
spin
Hall
effect
lays
the
foundation
for
topologically
protected
manipulation
of
waves,
but
is
restricted
to
one-dimensional-lower
boundaries
systems
and
hence
limits
diversity
integration
topological
photonic
devices.
Recently,
conventional
bulk-boundary
correspondence
band
topology
has
been
extended
higher-order
cases
that
enable
explorations
states
with
codimensions
larger
than
one
such
as
hinge
corner
states.
Here,
we
demonstrate
a
in
two-dimensional
crystal.
Owing
non-trivial
pseudospin-pseudospin
coupling,
observe
directional
localization
photons
at
corners
opposite
pseudospin
polarizations
through
pseudospin-momentum-locked
edge
resembling
manner.
Our
work
inspires
an
unprecedented
route
transport
trap
spinful
supporting
potential
applications
devices
lasers
chiral
emitters.
Advances In Physics,
Journal Year:
2020,
Volume and Issue:
69(3), P. 249 - 435
Published: July 2, 2020
A
review
is
given
on
the
foundations
and
applications
of
non-Hermitian
classical
quantum
physics.
First,
key
theorems
central
concepts
in
linear
algebra,
including
Jordan
normal
form,
biorthogonality,
exceptional
points,
pseudo-Hermiticity,
parity-time
symmetry,
are
delineated
a
pedagogical
mathematically
coherent
manner.
Building
these,
we
provide
an
overview
how
diverse
systems,
ranging
from
photonics,
mechanics,
electrical
circuits,
acoustics
to
active
matter,
can
be
used
simulate
wave
In
particular,
discuss
rich
unique
phenomena
found
therein,
such
as
unidirectional
invisibility,
enhanced
sensitivity,
topological
energy
transfer,
perfect
absorption,
single-mode
lasing,
robust
biological
transport.
We
then
explain
detail
operators
emerge
effective
description
open
systems
basis
Feshbach
projection
approach
trajectory
approach.
their
physical
relevant
variety
fields,
atomic,
molecular
optical
physics,
mesoscopic
nuclear
physics
with
emphasis
prominent
subjects
regimes,
resonances,
superradiance,
continuous
Zeno
effect,
critical
phenomena,
Dirac
spectra
chromodynamics,
nonunitary
conformal
field
theories.
Finally,
introduce
notion
band
topology
complex
present
classifications
by
providing
proof,
first
this
complete
manner,
well
number
instructive
examples.
Other
topics
related
nonreciprocal
transport,
speed
limits,
walk,
also
reviewed.
In
the
presence
of
crystalline
symmetries,
certain
topological
insulators
present
a
filling
anomaly:
mismatch
between
number
electrons
in
an
energy
band
and
required
for
charge
neutrality.
this
paper,
we
show
that
anomaly
can
arise
when
corners
are
introduced
$C_n$-symmetric
with
vanishing
polarization,
having
as
consequence
existence
corner-localized
charges
quantized
multiples
$\frac{e}{n}$.
We
characterize
systematically
build
indices
relate
symmetry
representations
occupied
bands
crystal
to
quanta
fractional
robustly
localized
at
its
corners.
When
additional
chiral
is
present,
$\frac{e}{2}$
corner
accompanied
by
zero-energy
states.
application
our
atomic
fragile
discuss
role
bound
disclinations
bulk
probes
these
phases.
Physical Review Letters,
Journal Year:
2019,
Volume and Issue:
122(23)
Published: June 14, 2019
The
studies
of
topological
phases
matter
have
been
developed
from
condensed
physics
to
photonic
systems,
resulting
in
fascinating
designs
robust
devices.
Recently,
higher-order
insulators
investigated
as
a
novel
phase
beyond
the
conventional
bulk-boundary
correspondence.
Previous
mainly
focused
on
multipole
systems
with
negative
coupling
between
lattice
sites.
Here
we
experimentally
demonstrate
that
second-order
insulating
without
can
be
realized
two-dimensional
dielectric
crystals.
We
visualize
both
one-dimensional
edge
states
and
zero-dimensional
corner
by
using
near-field
scanning
technique.
Our
findings
open
new
research
frontiers
for
provide
mechanism
light
manipulating
hierarchical
way.
Physical Review Letters,
Journal Year:
2019,
Volume and Issue:
122(23)
Published: June 14, 2019
Recently,
higher-order
topological
phases
that
do
not
obey
the
usual
bulk-edge
correspondence
principle
have
been
introduced
in
electronic
insulators
and
brought
into
classical
systems,
featuring
in-gap
corner
or
hinge
states.
In
this
Letter,
using
near-field
scanning
measurements,
we
show
direct
observation
of
states
second-order
photonic
crystal
slabs
consisting
periodic
dielectric
rods
on
a
perfect
electric
conductor.
Based
generalized
two-dimensional
Su-Schrieffer-Heeger
model,
emergence
roots
nonzero
edge
dipolar
polarization
instead
bulk
quadrupole
polarization.
We
demonstrate
transition
Zak
by
tuning
intracell
distances
between
two
neighboring
rods.
also
directly
observe
one-dimensional
zero-dimensional
microwave
regime.
Our
work
presents
slab
is
powerful
platform
to
paves
way
study
insulators.
Optica,
Journal Year:
2019,
Volume and Issue:
6(6), P. 786 - 786
Published: May 31, 2019
Topological
phonics
has
emerged
as
a
novel
approach
to
engineer
the
flow
of
light
and
provides
unprecedented
means
for
developing
diverse
photonic
elements,
including
robust
optical
waveguides
immune
structural
imperfections.
However,
development
nanoscale
standing-wave
cavities
in
topological
photonics
is
rather
slow,
despite
its
importance
when
building
densely-integrated
integrated
circuits.
In
this
Letter,
we
report
crystal
nanocavity
based
on
corner
state,
supported
at
90-degrees-angled
rim
two
dimensional
crystal.
A
combination
bulk-edge
edge-corner
correspondences
guarantees
presence
higher-order
state
hierarchical
manner.
We
experimentally
observed
mode
that
tightly
localized
space
while
supporting
high
Q
factor
over
2,000,
verifying
promise
nanocavity.
These
results
cast
new
way
introduce
nanocavities
platforms.
