44,912 research outputs found
Study of 0- phase transition in hybrid superconductor-InSb nanowire quantum dot devices
Hybrid superconductor-semiconducting nanowire devices provide an ideal
platform to investigating novel intragap bound states, such as the Andreev
bound states (ABSs), Yu-Shiba-Rusinov (YSR) states, and the Majorana bound
states. The competition between Kondo correlations and superconductivity in
Josephson quantum dot (QD) devices results in two different ground states and
the occurrence of a 0- quantum phase transition. Here we report on
transport measurements on hybrid superconductor-InSb nanowire QD devices with
different device geometries. We demonstrate a realization of continuous
gate-tunable ABSs with both 0-type levels and -type levels. This allow us
to manipulate the transition between 0 and junction and explore charge
transport and spectrum in the vicinity of the quantum phase transition regime.
Furthermore, we find a coexistence of 0-type ABS and -type ABS in the same
charge state. By measuring temperature and magnetic field evolution of the
ABSs, the different natures of the two sets of ABSs are verified, being
consistent with the scenario of phase transition between the singlet and
doublet ground state. Our study provides insights into Andreev transport
properties of hybrid superconductor-QD devices and sheds light on the crossover
behavior of the subgap spectrum in the vicinity of 0- transition
Low-field magnetotransport in graphene cavity devices
Confinement and edge structures are known to play significant roles in
electronic and transport properties of two-dimensional materials. Here, we
report on low-temperature magnetotransport measurements of lithographically
patterned graphene cavity nanodevices. It is found that the evolution of the
low-field magnetoconductance characteristics with varying carrier density
exhibits different behaviors in graphene cavity and bulk graphene devices. In
the graphene cavity devices, we have observed that intravalley scattering
becomes dominant as the Fermi level gets close to the Dirac point. We associate
this enhanced intravalley scattering to the effect of charge inhomogeneities
and edge disorder in the confined graphene nanostructures. We have also
observed that the dephasing rate of carriers in the cavity devices follows a
parabolic temperature dependence, indicating that the direct Coulomb
interaction scattering mechanism governs the dephasing at low temperatures. Our
results demonstrate the importance of confinement in carrier transport in
graphene nanostructure devices.Comment: 13 pages, 5 figure
A Bjorken sum rule for semileptonic decays to ground and excited charmed baryon states
We derive a Bjorken sum rule for semileptonic decays to ground and
low-lying negative-parity excited charmed baryon states, in the heavy quark
limit. We discuss the restriction from this sum rule on form factors and
compare it with some models.Comment: 10 pages, RevTex, no figure, Alberta Thy--26--9
Schottky barrier and contact resistance of InSb nanowire field effect transistors
Understanding of the electrical contact properties of semiconductor nanowire
(NW) field effect transistors (FETs) plays a crucial role in employing
semiconducting NWs as building blocks for future nanoelectronic devices and in
the study of fundamental physics problems. Here, we report on a study of the
contact properties of Ti/Au, a widely used contact metal combination, to
individual InSb NWs via both two-probe and four-probe transport measurements.
We show that a Schottky barrier of height is
present at the metal-InSb NW interfaces and its effective height is gate
tunable. The contact resistance () in the InSb NWFETs is also
analyzed by magnetotransport measurements at low temperatures. It is found that
at on-state exhibits a pronounced magnetic field dependent
feature, namely it is increased strongly with increasing magnetic field after
an onset field . A qualitative picture that takes into account
magnetic depopulation of subbands in the NWs is provided to explain the
observation. Our results provide a solid experimental evidence for the presence
of a Schottky barrier at Ti/Au-InSb NW interfaces and can be used as a basis
for design and fabrication of novel InSb NW based nanoelectronic devices and
quantum devices.Comment: 12 pages, 4 figure
Microstructural Evolution in Austenitic Stainless Steels Irradiated by Neutrons with Improved Control
Nucleation and growth of interstitial type dislocation loops were investigated by fusion neutron irradiation and fission neutron irradiations with improved control. The density of loops formed by both irradiations increased linearly with the fluence. The average size of loops also increased. The rate equation analysis showed that the loops were nucleated directly by the defect processes in a cascade zone, not by the reaction among the freely migrating point defects in the matrix. If the rate of loop formation is assumed to be directly proportional to the energy of a primary knock-on atom (PKA) produced by a neutron, the threshold energy of 80 keV and the rate of loop formation of 0.05 were obtained
Excitations of surface plasmon polaritons in double layer metal grating structures
We study the light scattering properties of double layer gratings (DLGs) made from Au on SiO2 substrates. It is found that surface plasmon polaritons (SPPs) can be excited in the DLGs for a separation of up to 150 nm between the two Au grating layers and the collective reflectance spectra exhibit a strong resonant peak and a closely lying dip as a result of the surface plasmon polariton excitations. It is also found that the angle-resolved specular reflectance spectra show a dip-peak pair structure, while the angle-resolved reflectance spectra of higher diffracted orders show a complementary peak-dip pair structure. Finally, operation of the DLGs for efficient wavelength demultiplexing is proposed and discussed in light of these results. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3690947
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