234 research outputs found
Emergent nanoscale superparamagnetism at oxide interfaces
Atomically sharp oxide heterostructures exhibit a range of novel physical
phenomena that do not occur in the parent bulk compounds. The most prominent
example is the appearance of highly conducting and superconducting states at
the interface between the band insulators LaAlO3 and SrTiO3. Here we report a
new emergent phenomenon at the LaMnO3/SrTiO3 interface in which an
antiferromagnetic insulator abruptly transforms into a magnetic state that
exhibits unexpected nanoscale superparamagnetic dynamics. Upon increasing the
thickness of LaMnO3 above five unit cells, our scanning nanoSQUID-on-tip
microscopy shows spontaneous formation of isolated magnetic islands of 10 to 50
nm diameter, which display random moment reversals by thermal activation or in
response to an in-plane magnetic field. Our charge reconstruction model of the
polar LaMnO3/SrTiO3 heterostructure describes the sharp emergence of
thermodynamic phase separation leading to nucleation of metallic ferromagnetic
islands in an insulating antiferromagnetic matrix. The model further suggests
that the nearby superparamagnetic-ferromagnetic transition can be gate tuned,
holding potential for applications in magnetic storage and spintronics
Probing dynamics and pinning of single vortices in superconductors at nanometer scales
The dynamics of quantized magnetic vortices and their pinning by materials
defects determine electromagnetic properties of superconductors, particularly
their ability to carry non-dissipative currents. Despite recent advances in the
understanding of the complex physics of vortex matter, the behavior of vortices
driven by current through a multi-scale potential of the actual materials
defects is still not well understood, mostly due to the scarcity of appropriate
experimental tools capable of tracing vortex trajectories on nanometer scales.
Using a novel scanning superconducting quantum interference microscope we
report here an investigation of controlled dynamics of vortices in lead films
with sub-Angstrom spatial resolution and unprecedented sensitivity. We
measured, for the first time, the fundamental dependence of the elementary
pinning force of multiple defects on the vortex displacement, revealing a far
more complex behavior than has previously been recognized, including striking
spring softening and broken-spring depinning, as well as spontaneous hysteretic
switching between cellular vortex trajectories. Our results indicate the
importance of thermal fluctuations even at 4.2 K and of the vital role of
ripples in the pinning potential, giving new insights into the mechanisms of
magnetic relaxation and electromagnetic response of superconductors.Comment: 15 pages and 5 figures (main text) + 15 pages and 11 figures
(supplementary material
Deep long asymmetric occultation in EPIC 204376071
We have discovered a young M star of mass 0.16 M and radius 0.63 R, likely in the Upper
Sco Association, that exhibits only a single 80 per cent deep occultation of 1-d duration. The
star has frequent flares and a low-amplitude rotational modulation, but is otherwise quiet over
160 d of cumulative observation during K2 campaigns C2 and C15. We discuss how such a
deep eclipse is not possible by one star crossing another in any binary or higher order stellar
system in which no mass transfer has occurred. The two possible explanations we are left with
are (1) orbiting dust or small particles (e.g. a disc bound to a smaller orbiting body, or unbound
dust that emanates from such a body); or (2) a transient accretion event of dusty material near
the corotation radius of the star. In either case, the time between such occultation events must
be longer than ∼80 d. We model a possible orbiting occulter both as a uniform elliptically
shaped surface (e.g. an inclined circular disc) and as a ‘dust sheet’ with a gradient of optical
depth behind its leading edge. The required masses in such dust features are then 3 × 1019 g
and 1019 g, for the two cases, respectively.Support for
G Z is provided by National Aeronautics and Space Administration
(NASA) through Hubble Fellowship grant HST-HF2-51402.001-A
awarded by the Space Telescope Science Institute, which is operated
by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555. A V’s work was supported
in part under a contract with the California Institute of Technology (Caltech)/Jet Propulsion Laboratory (JPL) funded by NASA
through the Sagan Fellowship Program executed by the NASA
Exoplanet Science Institute. E R N is supported by an National Science Foundation (NSF) Astronomy and Astrophysics Postdoctoral
Fellowship under award AST-1602597 We thank Allan R. Schmitt
and Troy Winarski for making their light curve examining software
tools LCTOOLS and AKO-TPF freely available. Some of the data
presented in this paper were obtained from the Mikulski Archive for
Space Telescopes (MAST). STScI is operated by the Association of
Universities for Research in Astronomy, Inc., under NASA contract
NAS5-26555. Support for MAST for non-HST data is provided
by the NASA Office of Space Science via grant NNX09AF08G
and by other grants and contracts. Some results are based on data
from the Carlsberg Meridian Catalogue 15 Data Access Service
at CAB (INTA-CSIC). This research has used IMCCE’s SkyBoT
VO tool
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