Infinite-layer
nickelates
stand
as
a
promising
frontier
in
the
exploration
of
unconventional
superconductivity.
Their
synthesis
through
topotactic
oxygen
reduction
from
parent
perovskite
phase
remains
complex
and
elusive
process.
This
study
delves
into
nano-scale
effects
lattice
transformation
within
LaNiO2
crystals.
Leveraging
high-resolution
scanning
transmission
electron
microscopy
spectroscopy,
our
investigations
uncover
panorama
structural
alterations,
including
grain
boundaries
coherent
twin
boundaries,
triggered
by
reduction-induced
transformations.
In
addition,
analyses
unveil
formation
an
oxygen-rich
disordered
transition
encircling
impurities
pervading
crystalline
domains
internal
strain
is
accommodated
boundary
formation.
By
unraveling
these
effects,
findings
provide
insights
microscopic
intricacies
process
elucidating
to
infinite-layer
nickelate
bulk
Revealing
the
momentum-resolved
electronic
structure
of
infinite-layer
nickelates
is
essential
for
understanding
this
class
unconventional
superconductors
but
has
been
hindered
by
formidable
challenges
in
improving
sample
quality.
In
work,
we
report
angle-resolved
photoemission
spectroscopy
superconducting
La
0.8
Sr
0.2
NiO
2
films
prepared
molecular
beam
epitaxy
and
situ
atomic-hydrogen
reduction.
The
measured
Fermi
topology
closely
matches
theoretical
calculations,
showing
a
large
Ni
dx2−y
–derived
sheet
that
evolves
from
hole-like
to
electron-like
along
k
z
three-dimensional
(3D)
electron
pocket
centered
at
Brillouin
zone
corner.
bands
show
mass
enhancement
(
m
*/
DFT
)
3,
while
3D
band
shows
negligible
renormalization.
Moreover,
states
also
display
dispersion
anomaly
higher
binding
energy,
reminiscent
waterfall
feature
kinks
observed
cuprates.
National Science Review,
Год журнала:
2024,
Номер
11(8)
Опубликована: Июнь 4, 2024
ABSTRACT
Superconducting
infinite-layer
(IL)
nickelates
offer
a
new
platform
for
investigating
the
long-standing
problem
of
high-temperature
superconductivity.
Many
models
were
proposed
to
understand
superconducting
mechanism
based
on
calculated
electronic
structure,
and
multiple
Fermi
surfaces
orbitals
involved
create
complications
controversial
conclusions.
Over
past
five
years,
lack
direct
measurements
structure
has
hindered
understanding
nickelate
superconductors.
Here
we
fill
this
gap
by
directly
resolving
structures
parent
compound
LaNiO2
La0.8Ca0.2NiO2
using
angle-resolved
photoemission
spectroscopy.
We
find
that
their
consist
quasi-2D
hole
pocket
3D
electron
at
Brillouin
zone
corner,
whose
volumes
change
upon
Ca
doping.
The
surface
topology
band
dispersion
closely
resemble
those
observed
in
hole-doped
cuprates.
However,
cuprate-like
exhibits
significantly
higher
doping
compared
cuprates,
highlighting
disparities
states
phase.
Our
observations
highlight
novel
aspects
IL
nickelates,
pave
way
toward
microscopic
family
its
Advanced Materials,
Год журнала:
2025,
Номер
unknown
Опубликована: Март 10, 2025
Several
reports
about
infinite-layer
nickelate
thin
films
suggest
that
the
superconducting
critical
temperature
versus
chemical
doping
phase
diagram
has
a
dome-like
shape,
similar
to
cuprates.
Here,
highly
reproducible
state
in
undoped
PrNiO2
grown
on
SrTiO3
are
demonstrated.
Scanning
transmission
electron
microscopy
measurements
show
coherent
with
no
visible
stacking-fault
defects,
an
overall
high
structural
quality
where
possible
unintentional
or
interstitial
oxygen,
if
present,
sum
well
below
measurable
threshold
of
technique.
X-ray
absorption
very
sharp
features
at
Ni
L3,2-edges
large
linear
dichroism,
indicating
preferential
hole
occupation
Ni1+-3
dx2-y2${\rm
d}_{x^2-y^2}$
orbitals
square
planar
geometry.
Resonant
inelastic
scattering
reveal
magnon
excitations
200
meV
energy
magnetic
Brillouin
zone
boundary,
resonant
Ni1
+
peak.
The
results
indicate
that,
when
properly
stabilized,
without
doping.
We
report
evidence
for
superconductivity
with
onset
temperatures
up
to
11
K
in
thin
films
of
the
infinite-layer
nickelate
parent
compound
NdNiO2.
A
combination
oxide
molecular
beam
epitaxy
and
atomic
hydrogen
reduction
yields
samples
high
crystallinity
low
residual
resistivities,
a
substantial
fraction
which
exhibit
superconducting
transitions.
survey
large
series
variety
techniques,
including
electrical
transport,
scanning
transmission
electron
microscopy,
x-ray
absorption
spectroscopy,
resonant
inelastic
scattering,
investigate
possible
origins
superconductivity.
propose
that
could
be
intrinsic
undoped
nickelates
but
suppressed
by
disorder
due
possibly
sign-changing
order
parameter,
finding
would
necessitate
reconsideration
phase
diagram.
Another
hypothesis
is
materials
can
hole
doped
from
randomly
dispersed
apical
oxygen
atoms,
suggest
an
alternative
pathway
achieving
Published
American
Physical
Society
2025
Nature Communications,
Год журнала:
2024,
Номер
15(1)
Опубликована: Авг. 27, 2024
Abstract
A
key
open
question
in
the
study
of
layered
superconducting
nickelate
films
is
role
that
hydrogen
incorporation
into
lattice
plays
appearance
state.
Due
to
challenges
stabilizing
highly
crystalline
square
planar
films,
are
prepared
by
deposition
a
more
stable
parent
compound
which
then
transformed
target
phase
via
topotactic
reaction
with
strongly
reducing
agent
such
as
CaH
2
.
Recent
studies,
both
experimental
and
theoretical,
have
introduced
possibility
from
may
be
critical
for
superconductivity.
In
this
work,
we
use
secondary
ion
mass
spectrometry
examine
La
1−
x
X
NiO
/
SrTiO
3
(
=
Ca
Sr)
Nd
6
Ni
5
O
12
NdGaO
along
non-superconducting
NdNiO
(Nd,Sr)NiO
We
find
no
evidence
extensive
across
broad
range
samples,
including
films.
Theoretical
calculations
indicate
broadly
energetically
unfavorable
these
systems,
supporting
our
conclusion
not
generally
required
achieve
state
square-planar
nickelates.
Advanced Materials,
Год журнала:
2024,
Номер
36(29)
Опубликована: Май 16, 2024
Since
their
discovery,
the
infinite-layer
nickelates
have
been
regarded
as
an
appealing
system
for
gaining
deeper
insights
into
high-temperature
superconductivity
(HTSC).
However,
synthesis
of
superconducting
samples
has
proven
to
be
challenging.
Here,
ultrahigh
vacuum
(UHV)
Physical Review Materials,
Год журнала:
2025,
Номер
9(5)
Опубликована: Май 27, 2025
The
family
of
infinite-layer
nickelates
promises
important
insights
into
the
mechanism
unconventional
superconductivity.
Since
superconductivity
has
so
far
only
been
observed
in
epitaxial
thin
films,
heteroepitaxy
with
substrate
or
a
capping
layer
possibly
plays
an
role.
Here,
we
use
soft
x-ray
spectroscopy
to
investigate
superlattices
as
potential
approach
for
targeted
material
design
high-temperature
superconductors.
We
observe
modulations
valence
state
and
oxygen
coordination
topotactically
reduced
artificial
repeating
interfaces
between
nickelate
layers
materials
commonly
used
substrates
layers.
Our
results
show
that
depending
on
interlayer
metallic
conductivity
akin
parent
compounds
is
achieved.
Depth-resolved
electronic
structure
measured
by
resonant
reflectivity
reveals
reconstructed
ligand
field
at
interface,
which
confined
one
two
unit
cells.
central
are
predominantly
monovalent
nickel,
but
linear
dichroism
analysis
considerable
disorder
removal
sites.
quantitative
correlation
this
future
modeling
strategies.
Published
American
Physical
Society
2025
Advanced Functional Materials,
Год журнала:
2024,
Номер
unknown
Опубликована: Сен. 11, 2024
Abstract
After
decades
of
research,
superconductivity
is
finally
found
in
nickel‐based
analogs
superconducting
cuprates,
with
infinite‐layer
(IL)
structure.
These
results
are
so
far
restricted
to
thin
films
the
case
IL‐nickelates.
Therefore,
nature
interface
substrate,
and
how
it
couples
film
properties
still
an
open
question.
Here,
using
scanning
transmission
electron
microscopy
(STEM)‐
energy
loss
spectroscopy
(EELS),
a
novel
p‐type
defined
by
SrO
termination
SrTiO
3
substrate
observed
(SC)
IL‐praseodymium
nickelate
samples.
Its
interfacial
charge
polarity
compared
previously
reported
n‐type
characterized
TiO
2
termination.
In
combination
ab‐initio
calculations,
that
influence
on
electronic
structure
local
does
not
extend
beyond
2–3
unit
cells
into
film.
This
decouples
direct
driving
superconductivity,
indicates
IL‐nickelate
do
have
universal
model.
Insights
spatial
hole‐distribution
SC
samples,
provided
monochromated
EELS
total
reflection‐hard
X‐ray
photoemission
spectroscopy,
suggest
this
particular
distribution
might
be
directly
influencing
superconductivity.
Advanced Materials Interfaces,
Год журнала:
2024,
Номер
unknown
Опубликована: Ноя. 25, 2024
Abstract
Unconventional
high‐temperature
superconductivity
has
long
been
a
captivating
puzzle
in
condensed
matter
physics.
The
1987
Nobel
Prize
Physics
celebrated
the
discovery
of
copper
oxide
ceramics.
Nearly
four
decades
later,
broad
class
superconducting
oxides
yet
to
be
demonstrated,
and
fundamental
understanding
pairing
mechanism
remains
inconclusive.
Recently,
nickel
have
emerged
as
new
superconductors,
beyond
copper,
where
correlated
phases
can
controlled
by
doping,
pressure,
strain,
dimensionality.
In
this
article,
we
provide
our
perspective
on
recent
developments
prospects
age
superconductivity.
