1,289 research outputs found
Tunneling between edge states in a quantum spin Hall system
We analyze a quantum spin Hall (QSH) device with a point contact connecting
two of its edges. The contact supports a net spin tunneling current that can be
probed experimentally via a two-terminal resistance measurement. We find that
the low-bias tunneling current and the differential conductance exhibit scaling
with voltage and temperature that depend nonlinearly on the strength of the
electron-electron interaction.Comment: 4 pages, 3 figures; published versio
Coordinated design of coding and modulation systems
The joint optimization of the coding and modulation systems employed in telemetry systems was investigated. Emphasis was placed on formulating inner and outer coding standards used by the Goddard Spaceflight Center. Convolutional codes were found that are nearly optimum for use with Viterbi decoding in the inner coding of concatenated coding systems. A convolutional code, the unit-memory code, was discovered and is ideal for inner system usage because of its byte-oriented structure. Simulations of sequential decoding on the deep-space channel were carried out to compare directly various convolutional codes that are proposed for use in deep-space systems
Edge Dynamics in a Quantum Spin Hall State: Effects from Rashba Spin-Orbit Interaction
We analyze the dynamics of the helical edge modes of a quantum spin Hall
state in the presence of a spatially non-uniform Rashba spin-orbit (SO)
interaction. A randomly fluctuating Rashba SO coupling is found to open a
scattering channel which causes localization of the edge modes for a weakly
screened electron-electron (e-e) interaction. A periodic modulation of the SO
coupling, with a wave number commensurate with the Fermi momentum, makes the
edge insulating already at intermediate strengths of the e-e interaction. We
discuss implications for experiments on edge state transport in a HgTe quantum
well.Comment: 4 pages, 2 figures; published versio
Nonequilibrium critical scaling from quantum thermodynamics
The emerging field of quantum thermodynamics is contributing important
results and insights into archetypal many-body problems, including quantum
phase transitions. Still, the question whether out-of-equilibrium quantities,
such as fluctuations of work, exhibit critical scaling after a sudden quench in
a closed system has remained elusive. Here, we take a novel approach to the
problem by studying a quench across an impurity quantum critical point. By
performing density matrix renormalization group computations on the
two-impurity Kondo model, we are able to establish that the irreversible work
produced in a quench exhibits finite-size scaling at quantum criticality. This
scaling faithfully predicts the equilibrium critical exponents for the
crossover length and the order parameter of the model, and, moreover, implies a
new exponent for the rescaled irreversible work. By connecting the irreversible
work to the two-impurity spin correlation function, our findings can be tested
experimentally.Comment: 6 pages, 4 figure
The effect of multiple paternity on genetic diversity during and after colonisation
In metapopulations, genetic variation of local populations is influenced by
the genetic content of the founders, and of migrants following establishment.
We analyse the effect of multiple paternity on genetic diversity using a model
in which the highly promiscuous marine snail Littorina saxatilis expands from a
mainland to colonise initially empty islands of an archipelago. Migrant females
carry a large number of eggs fertilised by 1 - 10 mates. We quantify the
genetic diversity of the population in terms of its heterozygosity: initially
during the transient colonisation process, and at long times when the
population has reached an equilibrium state with migration. During
colonisation, multiple paternity increases the heterozygosity by 10 - 300 % in
comparison with the case of single paternity. The equilibrium state, by
contrast, is less strongly affected: multiple paternity gives rise to 10 - 50 %
higher heterozygosity compared with single paternity. Further we find that far
from the mainland, new mutations spreading from the mainland cause bursts of
high genetic diversity separated by long periods of low diversity. This effect
is boosted by multiple paternity. We conclude that multiple paternity
facilitates colonisation and maintenance of small populations, whether or not
this is the main cause for the evolution of extreme promiscuity in Littorina
saxatilis.Comment: 7 pages, 5 figures, electronic supplementary materia
Local Spectral Weight of a Luttinger Liquid: Effects from Edges and Impurities
We calculate the finite-temperature local spectral weight (LSW) of a
Luttinger liquid with an "open" (hard wall) boundary. Close to the boundary the
LSW exhibits characteristic oscillations indicative of spin-charge separation.
The line shape of the LSW is also found to have a Fano-like asymmetry, a
feature originating from the interplay between electron-electron interaction
and scattering off the boundary. Our results can be used to predict how edges
and impurities influence scanning tunneling microscopy (STM) of one-dimensional
electron systems at low temperatures and voltage bias. Applications to STM on
single-walled carbon nanotubes are discussed.Comment: 15 pages, 10 figues, The latest version in pdf format is available at
http://www.physik.uni-kl.de/eggert/papers/LSW-LL.pd
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