success in this direction by
demonstrating that a mix of
processing and postsynthesis
charging can overcome these
problems. Synthesis of com-
positionally graded core-shell
quantum dots followed by a
carrier charging step provides
stable, slow-threshold lasing.
—ISO
Science, this issue p. 672GEOCHEMISTRY
Diamond window into
the deep mantle
Helium isotopes provide a
window into the very deepest
and oldest parts of Earth’s CREDITS (FROM TOP): NORMANET AL.; IMAGE: RICHARD TROUVE652 16 AUGUST 2019 • VOL 365 ISSUE 6454 sciencemag.org SCIENCE
voluminous mantle. However,
several processes tend to
obscure the helium isotope
signal from reservoirs in basal-
tic lavas that have erupted at
the surface. Timmerman et al.
identified a set of diamonds
that formed deep within Earth
and were rapidly erupted,
which have avoided near-sur-
face contamination. They find
evidence for a deep, primordial
rock source along with mixing
of sediments from old subduct-
ing plates. The signatures
extracted from these diamonds
have implications for chemical
and dynamic models of Earth.
—BG
Science, this issue p. 692GRAVITATION
Gravitational redshift in
the Galactic Center
General relativity predicts that
light emitted by an object in a
strong gravitational field—for
example, close to a black hole—
should be shifted to longer
wavelengths. This gravitational
redshift does not exist in the
Newtonian theory of gravity.
Do et al. monitored the position
and spectrum of the star S0-2
as it passed Sagittarius A*, the
supermassive black hole at the
center of the Milky Way. Around
the closest part of S0-2’s
16-year orbit, they detected the
effect of gravitational redshift
Edited by Michael FunkIN SCIENCE JOURNALS
RESEARCH
Visualizing memory
recall in the brain
Norman et al., p. 657on its spectrum. These results
are more consistent with gen-
eral relativity than Newtonian
gravity at the 5s level. —KTS
Science, this issue p. 664OPTICS
Switching on quantum
dot lasers
The optical properties of
quantum dots can be tailored
with alterations to their size
and composition. Developing
quantum dots as low-threshold
laser sources requires over-
coming problems associated
with carrier recombination and
stability. Kozlov et al. reportPEROVSKITESStrain-stabilized
perovskites
T
he perovskite materials used
for solar cells and light-emit-
ting diodes (which are black
in color) are generally less
stable at room temperature
than the electronically inactive
nonperovskite phases (which are
yellow in color). Steele et al. show
that for CsPbI 3 , strain induced
in a thin film after annealing the
material to 330°C and then rapidly
cooling it to room temperature
kinetically trapped the black phase.
Grazing-incidence wide-angle x-ray
scattering revealed the crystal
distortions and texture formation
created by interfacial strain. —PDS
Science, this issue p. 679X-ray scattering images of a perovskite
material (under) used in solar cells (overlay)