2,729 research outputs found
Non-Abelian Majorana modes protected by an emergent second Chern number
The search for topological superconductors and non-Abelian Majorana modes
ranks among the most fascinating topics in condensed matter physics. There now
exist several fundamental superconducting phases which host symmetry protected
or chiral Majorana modes. The latter, namely the chiral Majorana modes are
protected by Chern numbers in even dimensions. Here we propose to observe novel
chiral Majorana modes by realizing Fulde-Ferrell-Larkin-Ovchinnikov state, i.e.
the pairing density wave (PDW) phase in a Weyl semimetal which breaks
time-reversal symmetry. Without symmetry protection, the 3D gapped PDW phase is
topologically trivial. However, a vortex line generated in such phase can host
chiral Majorana modes, which are shown to be protected by an emergent second
Chern number of a synthetic 4D space generalized from the PDW phase. We further
show that these chiral modes in the vortex rings obey 3D non-Abelian
loop-braiding statistics, which can be applied to topological quantum
computation.Comment: 5 pages + supplementary matrial. Reference and some discussions are
update
Spin dynamics in the strong spin-orbit coupling regime
We study the spin dynamics in a high-mobility two dimensional electron gas
(2DEG) with generic spin-orbit interactions (SOIs). We derive a set of spin
dynamic equations which capture the purely exponential to the damped
oscillatory spin evolution modes observed in different regimes of SOI strength.
Hence we provide a full treatment of the D'yakonov-Perel's mechanism by using
the microscopic linear response theory from the weak to the strong SOI limit.
We show that the damped oscillatory modes appear when the electron scattering
time is larger than half of the spin precession time due to the SOI, in
agreement with recent observations. We propose a new way to measure the
scattering time and the relative strength of Rashba and linear Dresselhaus SOIs
based on these modes and optical grating experiments. We discuss the physical
interpretation of each of these modes in the context of Rabi oscillation.Comment: 8 pages, 9 figure
Topological Spin Texture in a Quantum Anomalous Hall Insulator
The quantum anomalous Hall (QAH) effect has been recently discovered in
experiment using thin-film topological insulator with ferromagnetic ordering
and strong spin-orbit coupling. Here we investigate the spin degree of freedom
of a QAH insulator and uncover a fundamental phenomenon that the edge states
exhibit topologically stable spin texture in the boundary when a chiral-like
symmetry is present. This result shows that edge states are chiral in both the
orbital and spin degrees of freedom, and the chiral edge spin texture
corresponds to the bulk topological states of the QAH insulator. We also study
the potential applications of the edge spin texture in designing
topological-state-based spin devices which might be applicable to future
spintronic technologies.Comment: 5 pages manuscript, 8+ pages supplementary information, 8 figures;
published versio
Practical Fine-grained Privilege Separation in Multithreaded Applications
An inherent security limitation with the classic multithreaded programming
model is that all the threads share the same address space and, therefore, are
implicitly assumed to be mutually trusted. This assumption, however, does not
take into consideration of many modern multithreaded applications that involve
multiple principals which do not fully trust each other. It remains challenging
to retrofit the classic multithreaded programming model so that the security
and privilege separation in multi-principal applications can be resolved.
This paper proposes ARBITER, a run-time system and a set of security
primitives, aimed at fine-grained and data-centric privilege separation in
multithreaded applications. While enforcing effective isolation among
principals, ARBITER still allows flexible sharing and communication between
threads so that the multithreaded programming paradigm can be preserved. To
realize controlled sharing in a fine-grained manner, we created a novel
abstraction named ARBITER Secure Memory Segment (ASMS) and corresponding OS
support. Programmers express security policies by labeling data and principals
via ARBITER's API following a unified model. We ported a widely-used, in-memory
database application (memcached) to ARBITER system, changing only around 100
LOC. Experiments indicate that only an average runtime overhead of 5.6% is
induced to this security enhanced version of application
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