251 research outputs found
Majorana spintronics
We propose a systematic magnetic-flux-free approach to detect, manipulate and
braid Majorana fermions in a semiconductor nanowire-based topological Josephson
junction by utilizing the Majorana spin degree of freedom. We find an intrinsic
-phase difference between spin-triplet pairings enforced by the Majorana
zeros modes (MZMs) at the two ends of a one-dimensional spinful topological
superconductor. This -phase is identified to be a spin-dependent
superconducting phase, referred to as the spin-phase, which we show to be
tunable by controlling spin-orbit coupling strength via electric gates. This
electric controllable spin-phase not only affects the coupling energy between
MZMs but also leads to a fractional Josephson effect in the absence of any
applied magnetic flux, which enables the efficient topological qubit readout.
We thus propose an all-electrically controlled superconductor-semiconductor
hybrid circuit to manipulate MZMs and to detect their non-Abelian braiding
statistics properties. Our work on spin properties of topological Josephson
effects potentially opens up a new thrust for spintronic applications with
Majorana-based semiconductor quantum circuits.Comment: 15 pages, 9 figures, replaced with published versio
Many-body localization in incommensurate models with a mobility edge
We review the physics of many-body localization in models with incommensurate
potentials. In particular, we consider one-dimensional quasiperiodic models
with single-particle mobility edges. Although a conventional perspective
suggests that delocalized states act as a thermalizing bath for the localized
states in the presence of of interactions, there is evidence that such systems
can display non-ergodicity. This is in part due to the fact that the
delocalized states do not have any kind of protection due to symmetry or
topology and are thus susceptible to localization. A study of non-interacting
incommensurate models shows that they admit extended, partially extended, and
fully localized many-body states. These models cannot thermalize dynamically
and remain localized upon the introduction of interactions. In particular, for
a certain range of energy, the system can host a non-ergodic extended (i.e.
metallic) phase in which the energy eigenstates violate the eigenstate
thermalization hypothesis (ETH) but the entanglement entropy obeys volume-law
scaling. The level statistics and entanglement growth also indicate the lack of
ergodicity in these models. The phenomenon of localization and non-ergodicity
in a system with interactions despite the presence of single-particle
delocalized states is closely related to the so-called "many-body proximity
effect" and can also be observed in models with disorder coupled to systems
with delocalized degrees of freedom. Many-body localization in systems with
incommensurate potentials (without single-particle mobility edges) have been
realized experimentally, and we show how this can be modified to study the the
effects of such mobility edges. Demonstrating the failure of thermalization in
the presence of a single-particle mobility edge in the thermodynamic limit
would indicate a more robust violation of the ETH.Comment: 17 pages, 14 figures, Review articl
Radiation Mechanisms for Semiconductor Devices and Packages
VLSI semiconductor devices are often the source of radiated electromagnetic emissions from electronic devices. Noise coupled from these devices to resonant structures on the printed circuit board, resonant cables or resonant enclosures can result in EMI problems that are difficult or expensive to solve at the board or system level. This paper reviews three mechanisms by which noise can be coupled from semiconductor devices and packages resulting in radiated electromagnetic emissions
Analysis of Chip-Level EMI using Near-Field Magnetic Scanning
Integrated circuits (ICs) are often a significant source of radiated energy from electronic systems. Well designed ICs maintain good control of the currents that they generate. However, poorly designed ICs can drive high-frequency noise currents onto nominally low-frequency input and output pins. These currents can excite unintentional radiating structures on the printed circuit board, resulting in radiated emissions that are difficult or expensive to control. The paper discusses the use of magnetic near-field scanning techniques to measure the current distribution in IC packages. This technique is applied to common ICs, including a clock driver, a memory module and a field programmable gate array (FPGA). Results show that near-field magnetic scanning is an effective tool for investigating chip-level EMI problems
Pyrite-Type CoS2 Nanoparticles Supported on Nitrogen-Doped Graphene for Enhanced Water Splitting
It is extremely meaningful to develop cheap, highly efficient, and stable bifunctional electrocatalysts for both hydrogen and oxygen evolution reactions (HER and OER) to promote large-scale application of water splitting technology. Herein, we reported the preparation of CoS2 nanoparticles supported on nitrogen-doped graphene (CoS2@N-GN) by one-step hydrothermal method and the enhanced electrochemical efficacy for catalyzing hydrogen and oxygen in water electrolysis. The CoS2@N-GN composites are composed of nitrogen-doped graphene and CoS2 nanocrystals with the average size of 73.5 nm. Benefitting from the improved electronic transfer and synergistic effect, the as-prepared CoS2@N-GN exhibits remarkable OER and HER performance in 1.0 M KOH, with overpotentials of 243 mV for OER and 204 mV for HER at 10 mA cm−2, and the corresponding Tafel slopes of 51.8 and 108 mV dec−1, respectively. Otherwise, the CoS2@N-GN hybrid also presents superior long-term catalytic durability. Moreover, an alkaline water splitting device assembled by CoS2@N-GN as both anode and cathode can achieve a low cell voltage of 1.53 V at 60 °C with a high faraday efficiency of 100% for overall water splitting. The tremendously enhanced electrochemical behaviors arise from favorable factors including small sized, homogenously dispersed novel CoS2 nanocrystals and coupling interaction with the underlying conductive nitrogen-doped graphene, which would provide insight into the rational design of transition metal chalcogenides for highly efficient and durable hydrogen and oxygen-involved electrocatalysis
Determination of High Frequency Package Currents from Near-Field Scan Data
Integrated circuits (ICs) are often a significant source of radiated energy from electronic systems. Near-field magnetic scanning is an effective tool for measuring the current distribution in IC packages and investigating chiplevel EMI problems. This paper discusses analysis of near-magnetic field scan data using tangential and normal field measurements. Results show that combining near-field scan results from probes with multiple orientations is an effective way to identify the current paths in IC packages
Understanding critical variables contributing to competitive advantages of international high-speed railway contractors
This article is devoted to identifying and explaining the critical variables contributing to competitive advantages in international High-Speed Railway (HSR) projects from the contractor’s perspective. A total of 24 variables were identified by the literature review and a pilot study. An international questionnaire survey was performed to obtain professional opinions from both practitioners and the academy. The 24 variables were ranked and clustered into 6 factors using exploratory factor analysis. Furthermore, a case study of the Early Train Operator project of the California HSR was carried out by the survey, interview, and first-hand data. The results indicated that the top six ranked variables are (1) None Accident History, (2) Eligibility & International Criteria, (3) Contract Reputation, (4) Marketing Strategy, (5) Risk Management Capability, and (6) Technical Responsiveness. Furthermore, the 24 variables are grouped into six dimensions: Glocalization, Marketing, Safety, Economics, Technology, and Responsibility. The case study indicated that the factor framework was suitable and tractable for the application. The findings of this paper could (1) assist international HSR contractors in obtaining a better understanding of the deeper determinates of competitive advantages and (2) serve as a valuable reference for developing their competitive advantages in the international HSR market
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