49 research outputs found
Hybridization of sub-gap states in one-dimensional superconductor/semiconductor Coulomb islands
We present measurements of one-dimensional superconductor-semiconductor
Coulomb islands, fabricated by gate confinement of a two-dimensional InAs
heterostructure with an epitaxial Al layer. When tuned via electrostatic side
gates to regimes without sub-gap states, Coulomb blockade reveals Cooper-pair
mediated transport. When sub-gap states are present, Coulomb peak positions and
heights oscillate in a correlated way with magnetic field and gate voltage, as
predicted theoretically, with (anti) crossings in (parallel) transverse
magnetic field indicating Rashba-type spin-orbit coupling. Overall results are
consistent with a picture of overlapping Majorana zero modes in finite wires
Relating Andreev Bound States and Supercurrents in Hybrid Josephson Junctions
We investigate superconducting quantum interference devices consisting of two
highly transmissive Josephson junctions coupled by a superconducting loop, all
defined in an epitaxial InAs/Al heterostructure. A novel device design allows
for independent measurements of the Andreev bound state spectrum within the
normal region of a junction and the resulting current-phase relation. We show
that knowledge of the Andreev bound state spectrum alone is enough to derive
the independently measured phase dependent supercurrent. On the other hand, the
opposite relation does not generally hold true as details of the energy
spectrum are averaged out in a critical current measurement. Finally,
quantitative understanding of field dependent spectrum and supercurrent require
taking into account the second junction in the loop and the kinetic inductance
of the epitaxial Al film
Coherent transport through a Majorana island in an Aharonov-Bohm interferometer
Majorana zero modes are leading candidates for topological quantum
computation due to non-local qubit encoding and non-abelian exchange
statistics. Spatially separated Majorana modes are expected to allow
phase-coherent single-electron transport through a topological superconducting
island via a mechanism referred to as teleportation. Here we experimentally
investigate such a system by patterning an elongated epitaxial InAs-Al island
embedded in an Aharonov-Bohm interferometer. With increasing parallel magnetic
field, a discrete sub-gap state in the island is lowered to zero energy
yielding persistent 1e-periodic Coulomb blockade conductance peaks (e is the
elementary charge). In this condition, conductance through the interferometer
is observed to oscillate in a perpendicular magnetic field with a flux period
of h/e (h is Planck's constant), indicating coherent transport of single
electrons through the islands, a signature of electron teleportation via
Majorana modes, could also be observed, suggesting additional non-Majorana
mechanisms for 1e transport through these moderately short wires
On the limits to mobility in InAs quantum wells with nearly lattice-matched barriers
The growth and the density dependence of the low temperature mobility of a
series of two-dimensional electron systems confined to un-intentionally doped,
low extended defect density InAs quantum wells with AlGaSb
barriers are reported. The electron mobility limiting scattering mechanisms
were determined by utilizing dual-gated devices to study the dependence of
mobility on carrier density and electric field independently. Analysis of the
possible scattering mechanisms indicate the mobility was limited primarily by
rough interfaces in narrow quantum wells and a combination of alloy disorder
and interface roughness in wide wells at high carrier density within the first
occupied electronic sub-band. At low carrier density the functional dependence
of the mobility on carrier density provided evidence of coulombic scattering
from charged defects. A gate-tuned electron mobility exceeding 750,000
cm/Vs was achieved at a sample temperature of 2 K.Comment: 23 pages, 7 figures, 1 tabl
The warm, the excited, and the molecular gas: GRB 121024A shining through its star-forming galaxy
We present the first reported case of the simultaneous metallicity
determination of a gamma-ray burst (GRB) host galaxy, from both afterglow
absorption lines as well as strong emission-line diagnostics. Using
spectroscopic and imaging observations of the afterglow and host of the
long-duration Swift GRB121024A at z = 2.30, we give one of the most complete
views of a GRB host/environment to date. We observe a strong damped Ly-alpha
absorber (DLA) with a hydrogen column density of log N(HI) = 21.88 +/- 0.10, H2
absorption in the Lyman-Werner bands (molecular fraction of log(f)~ -1.4;
fourth solid detection of molecular hydrogen in a GRB-DLA), the nebular
emission lines H-alpha, H-beta, [O II], [O III] and [N II], as well as metal
absorption lines. We find a GRB host galaxy that is highly star-forming (SFR ~
40 solar masses/yr ), with a dust-corrected metallicity along the line of sight
of [Zn/H]corr = -0.6 +/- 0.2 ([O/H] ~ -0.3 from emission lines), and a
depletion factor [Zn/Fe] = 0.85 +/- 0.04. The molecular gas is separated by 400
km/s (and 1-3 kpc) from the gas that is photoexcited by the GRB. This implies a
fairly massive host, in agreement with the derived stellar mass of
log(M/M_solar ) = 9.9+/- 0.2. We dissect the host galaxy by characterising its
molecular component, the excited gas, and the line-emitting star-forming
regions. The extinction curve for the line of sight is found to be unusually
flat (Rv ~15). We discuss the possibility of an anomalous grain size
distributions. We furthermore discuss the different metallicity determinations
from both absorption and emission lines, which gives consistent results for the
line of sight to GRB 121024A.Comment: 20 pages, 11 figures, accepted by MNRA
The warm, the excited, and the molecular gas: GRB 121024A shining through its star-forming galaxy★
We present the first reported case of the simultaneous metallicity determination of a gamma-ray burst (GRB) host galaxy, from both afterglow absorption lines as well as strong emission-line diagnostics. Using spectroscopic and imaging observations of the afterglow and host of the long-duratio
Pre- and early-postnatal nutrition modify gene and protein expressions of muscle energy metabolism markers and phospholipid fatty acid composition in a muscle type specific manner in sheep.
We previously reported that undernutrition in late fetal life reduced whole-body insulin sensitivity in adult sheep, irrespective of dietary exposure in early postnatal life. Skeletal muscle may play an important role in control of insulin action. We therefore studied a range of putative key muscle determinants of insulin signalling in two types of skeletal muscles (longissimus dorsi (LD) and biceps femoris (BF)) and in the cardiac muscle (ventriculus sinister cordis (VSC)) of sheep from the same experiment. Twin-bearing ewes were fed either 100% (NORM) or 50% (LOW) of their energy and protein requirements during the last trimester of gestation. From day-3 postpartum to 6-months of age (around puberty), twin offspring received a high-carbohydrate-high-fat (HCHF) or a moderate-conventional (CONV) diet, whereafter all males were slaughtered. Females were subsequently raised on a moderate diet and slaughtered at 2-years of age (young adults). The only long-term consequences of fetal undernutrition observed in adult offspring were lower expressions of the insulin responsive glucose transporter 4 (GLUT4) protein and peroxisome proliferator-activated receptor gamma, coactivator 1α (PGC1α) mRNA in BF, but increased PGC1α expression in VSC. Interestingly, the HCHF diet in early postnatal life was associated with somewhat paradoxically increased expressions in LD of a range of genes (but not proteins) related to glucose uptake, insulin signalling and fatty acid oxidation. Except for fatty acid oxidation genes, these changes persisted into adulthood. No persistent expression changes were observed in BF and VSC. The HCHF diet increased phospholipid ratios of n-6/n-3 polyunsaturated fatty acids in all muscles, even in adults fed identical diets for 1½ years. In conclusion, early postnatal, but not late gestation, nutrition had long-term consequences for a number of determinants of insulin action and metabolism in LD. Tissues other than muscle may account for reduced whole body insulin sensitivity in adult LOW sheep
Effects of butter from mountain-pasture grazing cows on risk markers of the metabolic syndrome compared with conventional Danish butter: a randomized controlled study.
BACKGROUND: There is considerable interest in dairy products from low-input systems, such as mountain-pasture grazing cows, because these products are believed to be healthier than products from high-input conventional systems. This may be due to a higher content of bioactive components, such as phytanic acid, a PPAR-agonist derived from chlorophyll. However, the effects of such products on human health have been poorly investigated. OBJECTIVE: To compare the effect of milk-fat from mountain-pasture grazing cows (G) and conventionally fed cows (C) on risk markers of the metabolic syndrome. DESIGN: In a double-blind, randomized, 12-week, parallel intervention study, 38 healthy subjects replaced part of their habitual dietary fat intake with 39 g fat from test butter made from milk from mountain-pasture grazing cows or from cows fed conventional winter fodder. Glucose-tolerance and circulating risk markers were analysed before and after the intervention. RESULTS: No differences in blood lipids, lipoproteins, hsCRP, insulin, glucose or glucose-tolerance were observed. Interestingly, strong correlations between phytanic acid at baseline and total (P<0.0001) and LDL cholesterol (P=0.0001) were observed. CONCLUSIONS: Lack of effects on blood lipids and inflammation indicates that dairy products from mountain-pasture grazing cows are not healthier than products from high-input conventional systems. Considering the strong correlation between LDL cholesterol and phytanic acid at baseline, it may be suggested that phytanic acid increases total and LDL cholesterol. TRIAL REGISTRATION: ClinicalTrials.gov, NCT0134358