248 research outputs found
Spray Deposited Nanocrystalline ZnO Transparent Electrodes: Role of Precursor Solvent
Nanocrystalline ZnO thin films were deposited by intermittent spray pyrolysis using different alcoholic and aqua-alcoholic precursor solvents. The XRD analysis reveals the polycrystallinity of hexagonal wurtzite type ZnO films with preferred c-axis orientation along [002] direction. The polycrystallinity increased due to use of aqua-alcoholic precursor solvent. The crystallite size was found to vary from 41.7 nm to 59.4 nm and blue shift in band-gap energy (3.225 eV to 3.255 eV) was observed due to aqua-alcoholic to alcoholic precursor solvent transition. The films deposited using alcoholic precursor solvent exhibited high transmittance (> 92 %) with low dark resistivity (10 – 3 Ω·cm) as compared to aqua-alcoholic precursor solvent. The effect of precursor solvent on resistivity, carrier concentration (η – /cm3), carrier mobility (μ – cm2V – 1s – 1), sheet resistance (Ω/) and figure of merit (ΦTC) is also reported. We recommend ethanol or methanol as a superior precursor solvent over aqua-alcoholic precursor solvent for deposition of device quality ZnO thin films
Supercurrent through a single transverse mode in nanowire Josephson junctions
Hybrid superconductor-semiconductor materials are fueling research in
mesoscopic physics and quantum technology. Recently demonstrated smooth
-Sn superconductor shells, due to the increased induced gap, are
expanding the available parameter space to new regimes. Fabricated on
quasiballistic InSb nanowires, with careful control over the hybrid interface,
Sn shells yield critical current-normal resistance products exceeding
temperature by at least an order of magnitude even when nanowire resistance is
of order 10k. In this regime Cooper pairs travel through a purely 1D
quantum wire for at least part of their trajectory. Here, we focus on the
evolution of supercurrent in magnetic field parallel to the nanowire. Long
decay up to fields of 1T is observed. At the same time, the decay for higher
occupied subbands is notably faster in some devices but not in others. We
analyze this using a tight-binding numerical model that includes the Zeeman,
orbital and spin-orbit effects. When the first subband is spin polarized, we
observe a dramatic suppression of supercurrent, which is also confirmed by the
model and suggests an absence of significant triplet supercurrent generation
Parity transitions in the superconducting ground state of hybrid InSb-Al Coulomb islands
The number of electrons in small metallic or semiconducting islands is
quantized. When tunnelling is enabled via opaque barriers this number can
change by an integer. In superconductors the addition is in units of two
electron charges (2e), reflecting that the Cooper pair condensate must have an
even parity. This ground state (GS) is foundational for all superconducting
qubit devices. Here, we study a hybrid superconducting-semiconducting island
and find three typical GS evolutions in a parallel magnetic field: a robust
2e-periodic even-parity GS, a transition to a 2e-periodic odd-parity GS,and a
transition from a 2e- to a 1e-periodic GS. The 2e-periodic odd-parity GS
persistent in gate-voltage occurs when a spin-resolved subgap state crosses
zero energy. For our 1e-periodic GSs we explicitly show the origin being a
single zero-energy state gapped from the continuum, i.e. compatible with an
Andreev bound states stabilized at zero energy or the presence of Majorana zero
modes
Electric field tunable superconductor-semiconductor coupling in Majorana nanowires
We study the effect of external electric fields on
superconductor-semiconductor coupling by measuring the electron transport in
InSb semiconductor nanowires coupled to an epitaxially grown Al superconductor.
We find that the gate voltage induced electric fields can greatly modify the
coupling strength, which has consequences for the proximity induced
superconducting gap, effective g-factor, and spin-orbit coupling, which all
play a key role in understanding Majorana physics. We further show that level
repulsion due to spin-orbit coupling in a finite size system can lead to
seemingly stable zero bias conductance peaks, which mimic the behavior of
Majorana zero modes. Our results improve the understanding of realistic
Majorana nanowire systems.Comment: 10 pages, 5 figures, supplemental information as ancillary fil
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
Quantized Majorana conductance
Majorana zero-modes hold great promise for topological quantum computing.
Tunnelling spectroscopy in electrical transport is the primary tool to identify
the presence of Majorana zero-modes, for instance as a zero-bias peak (ZBP) in
differential-conductance. The Majorana ZBP-height is predicted to be quantized
at the universal conductance value of 2e2/h at zero temperature. Interestingly,
this quantization is a direct consequence of the famous Majorana symmetry,
'particle equals antiparticle'. The Majorana symmetry protects the quantization
against disorder, interactions, and variations in the tunnel coupling. Previous
experiments, however, have shown ZBPs much smaller than 2e2/h, with a recent
observation of a peak-height close to 2e2/h. Here, we report a quantized
conductance plateau at 2e2/h in the zero-bias conductance measured in InSb
semiconductor nanowires covered with an Al superconducting shell. Our
ZBP-height remains constant despite changing parameters such as the magnetic
field and tunnel coupling, i.e. a quantized conductance plateau. We distinguish
this quantized Majorana peak from possible non-Majorana origins, by
investigating its robustness on electric and magnetic fields as well as its
temperature dependence. The observation of a quantized conductance plateau
strongly supports the existence of non-Abelian Majorana zero-modes in the
system, consequently paving the way for future braiding experiments.Comment: 5 figure
Exposure to Weight Management Counseling Among Students at 8 U.S. Medical Schools
INTRODUCTION: Clinical guidelines support physician intervention consistent with the Ask, Advise, Assess, Assist, Arrange framework for adults who have obesity. However, weight management counseling curricula vary across medical schools. It is unknown how frequently students receive experiences in weight management counseling, such as instruction, observation, and direct experience.
METHODS: A cross-sectional survey, conducted in 2017, of 730 third-year medical students in 8 U.S. medical schools assessed the frequency of direct patient, observational, and instructional weight management counseling experiences that were reported as summed scores with a range of 018. Analysis was completed in 2017.
RESULTS: Students reported the least experience with receiving instruction (6.5, SD=3.9), followed by direct patient experience (8.6, SD=4.8) and observational experiences (10.3, SD=5.0). During the preclinical years, 79% of students reported a total of \u3c /=3 hours of combined weight management counseling instruction in the classroom, clinic, doctor\u27s office, or hospital. The majority of the students (59%-76%) reported never receiving skills-based instruction for weight management counseling. Of the Ask, Advise, Assess, Assist, Arrange framework, scores were lowest for assisting the patient to achieve their agreed-upon goals (31%) and arranging follow-up contact (22%).
CONCLUSIONS: Overall exposure to weight management counseling was less than optimal. Medical school educators can work toward developing a more coordinated approach to weight management counseling. Inc
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