84 research outputs found
Searching for Majorana quasiparticles at vortex cores in iron-based superconductors
The unambiguous detection of the Majorana zero mode (MZM), which is essential
for future topological quantum computing, has been a challenge in recent
condensed matter experiments. The MZM is expected to emerge at the vortex core
of topological superconductors as a zero-energy vortex bound state (ZVBS),
amenable to detection using scanning tunneling microscopy/spectroscopy
(STM/STS). However, the typical energy resolution of STM/STS has made it
challenging to distinguish the MZM from the low-lying trivial vortex bound
states. Here, we review the recent high-energy-resolution STM/STS experiments
on the vortex cores of Fe(Se,Te), where the MZM is expected to emerge, and the
energy of the lowest trivial bound states is reasonably high. Tunneling spectra
taken at the vortex cores exhibit a ZVBS well below any possible trivial state,
suggesting its MZM origin. However, it should be noted that ZVBS is a necessary
but not sufficient condition for the MZM; a qualitative feature unique to the
MZM needs to be explored. We discuss the current status and issues in the
pursuit of such Majorananess, namely the level sequence of the vortex bound
states and the conductance plateau of the ZVBS. We also argue for future
experiments to confirm the Majorananess, such as the detection of the doubling
of the shot noise intensity and spin polarization of the MZM.Comment: 22 pages, 7 figure
Local density of states and superconducting gap in the iron chalcogenide superconductor FeSeTe observed by scanning tunneling spectroscopy
We report on the first investigation of the quasiparticle local density of
states and superconducting gap in the iron chalcogenide superconductor
FeSeTe ( K). The surface of
a cleaved crystal revealed an atomic square lattice, superimposed on the
inhomogeneous background, with a lattice constant of \AA without any
reconstruction. Tunneling spectra measured at 4.2 K exhibit the superconducting
gap, which completely disappears at 18 K, with a magnitude of meV,
corresponding to .In stark contrast
to the cuprate superconductors, the value of the observed superconducting gap
is relatively homogeneous, following a sharp distribution with a small standard
deviation of 0.23 meV. Conversely, the normal-state local density of states
observed above shows spatial variation over a wide energy
range of more than 1 eV, probably due to the excess iron present in the
crystal.Comment: 4 pages, 5 figure
Local Measurement of Microwave Response with Local Tunneling Spectra Using Near Field Microwave Microscopy
We have designed and built a near-field scanning microwave microscope, which
has been used to measure the local microwave response and the local
density-of-states (LDOS) in the area including the boundary between the gold
deposited and the non-deposited region on highly-orientated pyrolytic graphite
at a frequency of about 7.3 GHz. We have succeeded in measuring the spatial
variation of both the LDOS and the surface resistance. It can be observed that
the surface resistance in gold deposited region with the metallic tunneling
spectra is smaller than that in the non-deposited region with the U-shaped
tunneling spectra.Comment: 3 pages, 3 figures
Vitreous levels of vascular endothelial growth factor in eyes with anterior hyaloidal fibrovascular proliferation
Takaki Kobayashi, Shigeki Machida, Takamitsu Fujiwara, Tadashi Ishibe, Daijiro KurosakaDepartment of Ophthalmology, Iwate Medical University School of Medicine, Iwate, JapanPurpose: To determine the intravitreal levels of vascular endothelial growth factor (VEGF) in eyes with anterior hyaloidal fibrovascular proliferation (AHFVP).Methods: Three eyes of three patients who underwent vitrectomy for proliferative diabetic retinopathy (PDR) and subsequently developed an AHFVP (AHFVP group) were studied. We measured the level of VEGF in vitreous samples collected at the primary and following operations by enzyme-linked immunosorbent assay. The vitreous levels of VEGF in 25 eyes of 22 patients with PDR were also studied as controls (PDR group).Results: The averaged VEGF level in the samples collected at the primary surgery was 1.98 ± 2.23 ng/mL in the PDR group, and it was 9.07, 1.94, and 8.07 ng/mL in the AHFVP cases. After the primary surgery, the VEGF level rose up to 49.50, 15.60, and 50.60 ng/mL at the subsequent surgeries for respective cases of the AHFVP group. These levels of VEGF were more than five times higher than the baseline at the primary surgery.Conclusion: The subsequent increase of the VEGF level after the primary surgery in eyes with an AHFVP suggests that the vitreous levels of VEGF are associated with the development of the AHFVP although only three eyes were studied.Keywords: VEGF, AHFVP, diabetic retinopath
Elevation by Oxidative Stress and Aging of Hypothalamic-Pituitary-Adrenal Activity in Rats and Its Prevention by Vitamin E
The present study was conducted in order to determine whether oxidative stress during aging involves dysfunction of the hypothalamic-pituitary-adrenal (HPA) axis in association with the emergence of cognitive deficits. When young rats were subjected to oxidative stress in the form of hyperoxia, thiobarbituric acid reactive substances, conjugated diene and lipid hydroperoxides increased markedly in the HPA axis. Vitamin E inhibited such increases in lipid peroxides in each organ. Levels of corticotrophin-releasing hormone in the hypothalamus and plasma levels of adrenocorticotrophic hormone and corticosterone were markedly elevated in young rats exposed to hyperoxia. However, young rats fed vitamin E-supplemented diets showed no abnormal hormone secretion, even after being subjected to hyperoxia. Furthermore, glucocorticosteroid receptors (GR) in pyramidal cells in the Cornus ammonis 1 region of the hippocampus in young rats were markedly decreased by oxidative stress. Similar phenomena were also observed in normal aged rats and young rats fed vitamin E-deficient diet kept in a normal atmosphere. Vitamin E supplementation prevented the decrease in GR in the hippocampus and the increase in corticosterone secretion caused by hyperoxia. These results suggest that oxidative stress induces oxidative damage in the hippocampus and the HPA axis during aging, resulting in a cognitive deficit in rats, and that negative-feedback inhibition on HPA activity was markedly dampened due to an increase in corticosterone levels caused by loss of GR
Sound velocity and elastic properties of Fe–Ni–S–Si liquid: the effects of pressure and multiple light elements
Fe–Ni–S–Si alloy is considered to be one of the plausible candidates of Mercury core material. Elastic properties of Fe–Ni–S–Si liquid are important to reveal the density profile of the Mercury core. In this study, we measured the P-wave velocity (VP) of Fe–Ni–S–Si (Fe73Ni10S10Si7, Fe72Ni10S5Si13, and Fe67Ni10S10Si13) liquids up to 17 GPa and 2000 K to study the effects of pressure, temperature, and multiple light elements (S and Si) on the VP and elastic properties.
The VP of Fe–Ni–S–Si liquids are less sensitive to temperature. The effect of pressure on the VP are close to that of liquid Fe and smaller than those of Fe–Ni–S and Fe–Ni–Si liquids. Obtained elastic properties are KS0 = 99.1(9.4) GPa, KS’ = 3.8(0.1) and ρ0 =6.48 g/cm3 for S-rich Fe73Ni10S10Si7 liquid and KS0 = 112.1(1.5) GPa, KS’ = 4.0(0.1) and ρ0=6.64 g/cm3 for Si-rich Fe72Ni10S5Si13 liquid. The VP of Fe–Ni–S–Si liquids locate in between those of Fe–Ni–S and Fe–Ni–Si liquids. This suggests that the effect of multiple light element (S and Si) on the VP is suppressed and cancel out the effects of single light elements (S and Si) on the VP. The effect of composition on the EOS in the Fe–Ni–S–Si system is indispensable to estimate the core composition combined with the geodesy data of upcoming Mercury mission
Potential endocrine effects of hypothalamic peptide "neurotensin" on pancreas in dogs
Effects of synthetic neurotensin on the endocrine pancreas were studied in nine normal and six hypophysectomized (10th to 14th day post-hypophysectomy) dogs. Synthetic neurotensin was administered into the superior pancreaticoduodenal artery, and plasma insulin and glucagon concentrations were measured radioimmunologically. In normal dogs, ten microgram/kg neurotensin administration brought about a mild hyperglycemic response and sharp and rapid increase of plasma insulin and glucagon concentrations in the superior pancreaticoduodenal vein. A biphasic insulin response was noted in the pancreatic vein. The results suggest that a large dose of neurotensin acts directly on the endocrine pancreas causing secretion of these hormones. In hypophysectomized dogs, basal levels of plasma insulin and glucagon were decreased and neurotensin had little effect on the endocrine pancreas even with the administration of a large dose.</p
- …