69 research outputs found
Real-space observation of short-period cubic lattice of skyrmions in MnGe
Emergent phenomena and functions arising from topological electron-spin
textures in real space or momentum space are attracting growing interest for
new concept of states of matter as well as for possible applications to
spintronics. One such example is a magnetic skyrmion, a topologically stable
nanoscale spin vortex structure characterized by a topological index.
Real-space regular arrays of skyrmions are described by combination of
multi-directional spin helixes. Nanoscale configurations and characteristics of
the two-dimensional skyrmion hexagonal-lattice have been revealed extensively
by real-space observations. Other three-dimensional forms of skyrmion lattices,
such as a cubic-lattice of skyrmions, are also anticipated to exist, yet their
direct observations remain elusive. Here we report real-space observations of
spin configurations of the skyrmion cubic-lattice in MnGe with a very short
period (~3 nm) and hence endowed with the largest skyrmion number density. The
skyrmion lattices parallel to the {100} atomic lattices are directly observed
using Lorentz transmission electron microscopes (Lorentz TEMs). It enables the
first simultaneous observation of magnetic skyrmions and underlying
atomic-lattice fringes. These results indicate the emergence of
skyrmion-antiskyrmion lattice in MnGe, which is a source of emergent
electromagnetic responses and will open a possibility of controlling
few-nanometer scale skyrmion lattices through atomic lattice modulations
Luminal acidification of diverse organelles by V-ATPase in animal cells
Eukaryotic cells contain organelles bounded by a single membrane in the cytoplasm. These organelles have differentiated to carry out various functions in the pathways of endocytosis and exocytosis. Their lumina are acidic, with pH ranging from 4.5 to 6.5. This article describes recent studies on these animal cell organelles
focusing on (1) the primary proton pump (vacuolar-type H+-ATPase) and (2) the functions of the organelle luminal acidity. We also discuss similarities and differences between vacuolar-type H+-ATPase and F-type ATPase. Our own studies and interests are emphasized
Molecular beam epitaxy of superconducting FeSeTe thin films interfaced with magnetic topological insulators
Engineering heterostructures with various types of quantum materials can
provide an intriguing playground for studying exotic physics induced by
proximity effect. Here, we report the successful synthesis of iron-based
superconductor FeSeTe (FST) thin films in the entire composition
of and its heterostructure with a magnetic topological
insulator by using molecular beam epitaxy. Superconductivity is observed in the
FST films with an optimal superconducting transition temperature
12 K at around x = 0.1. We found that superconductivity survives in the very
Te-rich films (), showing stark contrast to bulk crystals with
suppression of superconductivity due to an appearance of bicollinear
antiferromagnetism accompanied by monoclinic structural transition. By
examining thickness t dependence on electrical transport properties, we
observed strong suppression of the structural transition in films below t
100 nm, suggesting that substrate effects may stabilize superconducting
phase near the interface. Furthermore, we fabricated all chalcogenide-based
heterointerface between FST and magnetic topological insulator
(Cr,Bi,Sb)Te for the first time, observing both superconductivity
and large anomalous Hall conductivity. The anomalous Hall conductivity
increases with decreasing temperature, approaching to the quantized value of
down to the measurable minimum temperature at . The result
suggests coexistence of magnetic and superconducting gaps at low temperatures
opening at the top and bottom surfaces, respectively. Our novel magnetic
topological insulator/superconductor heterostructure could be an ideal platform
to explore chiral Majorana edge mode
Direct observations of spin fluctuations in spin-hedgehog-anti-hedgehog lattice states in MnSiGe ( and ) at zero magnetic field
The helimagnetic compounds MnSiGe show the three-dimensional
multiple- order as referred to as spin-hedgehog-anti-hedgehog (SHAH)
lattice. Two representative forms of SHAH are cubic-3 lattice with and tetrahedral-4 lattice with ,
which show up typically for and for , respectively. Here,
we have investigated the spin fluctuations in the MnSiGe
polycrystalline samples with and by using the time-of-flight
(TOF) neutron inelastic scattering and MIEZE-type neutron spin echo techniques
to elucidate the microscopic origin of the unconventional Hall effect in the
SHAH lattice states. This research is motivated by the observation of a sign
change in the unconventional Hall resistivity as a function of temperature [Y.
Fujishiro et al., Nat. Comm. , 1059 (2019)]. The present results
reveal the correspondences between the temperature ranges where the positive
Hall resistivity and spin fluctuations are observed. These results agree well
with the theoretical model of the conduction electrons scattered by the
fluctuating spin clusters with a non-zero average of sign-biased scalar spin
chirality as a mechanism of the positive Hall resistivity [H. Ishizuka and N.
Nagaosa, Sci. Adv. , eaap9962 (2018)].Comment: 10 pages, 8 figure
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