238 research outputs found
Robustness of Majorana Modes and Minigaps in a Spin-Orbit-Coupled Semiconductor-Superconductor Heterostructure
We study the robustness of Majorana zero energy modes and minigaps of
quasiparticle excitations in a vortex by numerically solving
Bogoliubov-deGennes equations in a heterostructure composed of an \textit{s}
-wave superconductor, a spin-orbit-coupled semiconductor thin film, and a
magnetic insulator. This heterostructure was proposed recently as a platform
for observing non-Abelian statistics and performing topological quantum
computation. The dependence of the Majorana zero energy states and the minigaps
on various physics parameters (Zeeman field, chemical potential, spin-orbit
coupling strength) is characterized. We find the minigaps depend strongly on
the spin-orbit coupling strength. In certain parameter region, the minigaps are
linearly proportional to the \textit{s}-wave superconducting pairing gap
, which is very different from the dependence in a
regular \textit{s-} or \textit{\p}-wave superconductor. We characterize the
zero energy chiral edge state at the boundary and calculate the STM signal in
the vortex core that shows a pronounced zero energy peak. We show that the
Majorana zero energy states are robust in the presence of various types of
impurities. We find the existence of impurity potential may increase the
minigaps and thus benefit topological quantum computation.Comment: 11 pages, 15 figure
Hole-doped semiconductor nanowire on top of an s-wave superconductor: A new and experimentally accessible system for Majorana fermions
Majorana fermions were envisioned by E. Majorana in 1935 to describe
neutrinos. Recently it has been shown that they can be realized even in a class
of electron-doped semiconductors, on which ordinary s-wave superconductivity is
proximity induced, provided the time reversal symmetry is broken by an external
Zeeman field above a threshold. Here we show that in a hole-doped semiconductor
nanowire the threshold Zeeman field for Majorana fermions can be very small for
some magic values of the hole density. In contrast to the electron-doped
systems, smaller Zeeman fields and much stronger spin-orbit coupling and
effective mass of holes allow the hole-doped systems to support Majorana
fermions in a parameter regime which is routinely realized in current
experiments.Comment: 5 pages, 3 figures, accepted for publication in Phys. Rev. Let
Majorana Fermions Under Uniaxial Stress in Semiconductor-Superconductor Heterostructures
Spin-orbit coupled semiconductor nanowires with Zeeman splitting in proximity
contact with bulk -wave superconductivity have recently been proposed as a
promising platform for realizing Majorana fermions. However, in this setup the
chemical potential of the nanowire is generally pinned by the Fermi surface of
the superconductor. This makes the tuning of the chemical potential by external
electrical gates, a crucial requirement for unambiguous detection of Majorana
fermions, very challenging in experiments. Here we show that tunable
topological superconducting regime supporting Majorana fermions can be realized
in semiconductor nanowires using uniaxial stress. For n-type nanowires the
uniaxial stress tunes the effective chemical potential, while for p-type
systems the effective pairing may also be modified by stress, thus
significantly enhancing the topological minigap. We show that the required
stress, of the order of 0.1%, is within current experimental reach using
conventional piezo crystals.Comment: 5 pages, 4 figures, to appear in Phys. Rev. B (Rapid Communication
ROUTING PROTOCOL FOR LOW POWER AND LOSSY NETWORKS
The techniques presented herein provide Routing Protocol for Low power and Lossy Networks (RPL) that enhances the incorporation of RPL Unaware Leaves (RULs) into a network while also improving the flexibility of the network deployment. Specifically, the techniques presented herein create one or more proxies for RULs that can reduce the number of messages a RUL needs to receive. Thus, a RUL can wake less and preserve its battery. The one or more proxies proxy IPv6 protocol, such as DHCPv6, for the RUL and maintain the keep alive state for RUL
A NOVEL TECHNIQUE TO PERFORM LARGE FILE UPDATES ON INTERNET OF THINGS (IOT) DEVICES USING BLOCK CHAIN IN LOW-POWER AND LOSSY NETWORKS (LLNS)
Proposed herein is an efficient large file update (e.g., a firmware update) technique that utilizes blockchain technology, rather than a classic centralized solution. This technique adopts a decentralized and distributed architecture to disseminate information, which may greatly reduce bandwidth occupation and accelerate the updating process. Various benefits may also be realized by this technique including, but not limited to: 1) making sure that each piece of a block is correct through a blockchain hash (e.g., a node could be aware of the legality of a file download before the whole file download is completed); 2) as opposed to a Multicast Protocol for Low-Power and Lossy Network (MPL) solution, all nodes do not need to conserve as many packets as possible in Random Access Memory (RAM), rather a block may be saved directly into non-volatile flash, which could mitigate the usage pressure for temporary buffers; and/or 3) as opposed to a centralized solution, this technique does not need to exchange information with a Network Management System (NMS), rather a node may pull missing blocks from its neighbors as long as they have them and, after two rounds of failures, it can turn to the NMS, which may not result in concurrent traffic to the NMS
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