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 $\Delta_{s}$, which is very different from the $\Delta_{s}^{2}$ 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 $s$-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