5,434 research outputs found
Inversion symmetry protected topological insulators and superconductors
Three dimensional topological insulator represents a class of novel quantum
phases hosting robust gapless boundary excitations, which is protected by
global symmetries such as time reversal, charge conservation and spin
rotational symmetry. In this work we systematically study another class of
topological phases of weakly interacting electrons protected by spatial
inversion symmetry, which generally don't support stable gapless boundary
states. We classify these inversion-symmetric topological insulators and
superconductors in the framework of K-theory, and construct their lattice
models. We also discuss quantized response functions of these
inversion-protected topological phases, which serve as their experimental
signatures.Comment: 9.5+2.5 pages, 4 figures, 2 table
Applications of Lerch's theorem and permutations concerning quadratic residues
Let be an odd prime. For each integer with , the famous
Zolotarev's Lemma says that the Legendre symbol is the sign of
the permutation of induced by multiplication by . The extension of
Zolotarev's result to the case of odd integers was shown by Frobenius. After
that, Lerch extended these to all positive integers. In this paper we explore
some applications of Lerch's result. For instance, we study permutations
involving arbitrary -th power residue modulo and primitive roots of a
power of . Finally, we discuss some permutation problems concerning
quadratic residues modulo . In particular, we confirm some conjectures posed
by Sun.Comment: 11 page
Generalized Compute-Compress-and-Forward
Compute-and-forward (CF) harnesses interference in wireless communications by
exploiting structured coding. The key idea of CF is to compute integer
combinations of codewords from multiple source nodes, rather than to decode
individual codewords by treating others as noise. Compute-compress-and-forward
(CCF) can further enhance the network performance by introducing compression
operations at receivers. In this paper, we develop a more general compression
framework, termed generalized compute-compress-and-forward (GCCF), where the
compression function involves multiple quantization-and-modulo lattice
operations. We show that GCCF achieves a broader compression rate region than
CCF. We also compare our compression rate region with the fundamental
Slepian-Wolf (SW) region. We show that GCCF is optimal in the sense of
achieving the minimum total compression rate. We also establish the criteria
under which GCCF achieves the SW region. In addition, we consider a two-hop
relay network employing the GCCF scheme. We formulate a sum-rate maximization
problem and develop an approximate algorithm to solve the problem. Numerical
results are presented to demonstrate the performance superiority of GCCF over
CCF and other schemes.Comment: 27 pages, 11 figures, submitted to IEEE Transaction on Information
Theor
Quantum phase transitions between bosonic symmetry protected topological phases in two dimensions: emergent and anyon superfluid
Inspired by Chern-Simons effective theory description of symmetry protected
topological (SPT) phases in two dimensions, we present a projective
construction for many-body wavefunctions of SPT phases. Using this projective
construction we can systematically write down trial wavefunctions of SPT phases
on a lattice. An explicit example of SPT phase with symmetry is
constructed for two types of bosons with filling
per site on square lattice. We study continuous phase transitions between
different -SPT phases based on projective construction. The effective
theory around the critical point is emergent with fermion number
. Such a continuous phase transition however needs fine tuning, and in
general there are intermediate phases between different -SPT phases. We
show that such an intermediate phase has the same response as an anyon
superconductor, and hence dub it "anyon superfluid". A schematic phase diagram
of interacting bosons with symmetry is depicted.Comment: 11 pages, 3 figures, published versio
Spin quantum Hall effects in a spin-1 topological paramagnet
AKLT state (or Haldane phase) in a spin-1 chain represents a large class of
gapped topological paramagnets, which hosts symmetry-protected gapless
excitations on the boundary. In this work we show how to realize this type of
featureless spin-1 states on a generic two-dimensional lattice. These states
have a gapped spectrum in the bulk but supports gapless edge states protected
by spin rotational symmetry along a certain direction, and are featured by spin
quantum Hall effect. Using fermion representation of integer-spins we show a
concrete example of such spin-1 topological paramagnets on kagome lattice, and
suggest a microscopic spin-1 Hamiltonian which may realize it.Comment: 5 pages, 2 figures, published version, references update
Output Feedback Tracking Control for a Class of Uncertain Systems subject to Unmodeled Dynamics and Delay at Input
Besides parametric uncertainties and disturbances, the unmodeled dynamics and
time delay at the input are often present in practical systems, which cannot be
ignored in some cases. This paper aims to solve output feedback tracking
control problem for a class of nonlinear uncertain systems subject to unmodeled
high-frequency gains and time delay at the input. By the additive
decomposition, the uncertain system is transformed to an uncertainty-free
system, where the uncertainties, disturbance and effect of unmodeled dynamics
plus time delay are lumped into a new disturbance at the output. Sequently,
additive decomposition is used to decompose the transformed system, which
simplifies the tracking controller design. To demonstrate the effectiveness,
the proposed control scheme is applied to three benchmark examples.Comment: 22 pages, 7 figure
Can deeply underdoped superconducting cuprates be topological superconductors?
The nodal superconducting gap is a hallmark of the cuprate high
T superconductors. Surprisingly recent angle-resolved photoemission
spectroscopy of deeply underdoped cuprates revealed a nodeless energy gap which
is adhered to the Fermi surface. Importantly this phenomenon is observed for
compounds across several different cuprate families. In this letter we propose
an exciting possibility, namely the fully gapped state is a topological
superconductor.Comment: 4 pages, 1 table, 3 figures + 4.5 pages supplemental material
An optimal consensus tracking control algorithm for autonomous underwater vehicles with disturbances
The optimal disturbance rejection control problem is considered for consensus
tracking systems affected by external persistent disturbances and noise.
Optimal estimated values of system states are obtained by recursive filtering
for the multiple autonomous underwater vehicles modeled to multi-agent systems
with Kalman filter. Then the feedforward-feedback optimal control law is
deduced by solving the Riccati equations and matrix equations. The existence
and uniqueness condition of feedforward-feedback optimal control law is
proposed and the optimal control law algorithm is carried out. Lastly,
simulations show the result is effectiveness with respect to external
persistent disturbances and noise
An explicit representation and enumeration for self-dual cyclic codes over of length
Let be a finite field of cardinality and a
positive integer. Using properties for Kronecker product of matrices and
calculation for linear equations over , an efficient method
for the construction of all distinct self-dual cyclic codes with length
over the finite chain ring is
provided. On that basis, an explicit representation for every self-dual cyclic
code of length over and an exact
formula to count the number of all these self-dual cyclic codes are given
High superconductivity at the FeSe/SrTiO Interface
In a recent experiment the superconducting gap of a single unit cell thick
FeSe film on SrTiO substrate is observed by scanning tunneling spectroscopy
and angle-resolved photoemission spectroscopy. The value of the superconducting
gap is much larger than that of the bulk FeSe under ambient pressure. In this
paper we study the effects of screening due to the ferroelectric phonons on
Cooper pairing. We conclude it can significantly enhance the energy scale of
Cooper pairing and even change the pairing symmetry. Our results also raise
some concerns on whether phonons can be completely ignored for bulk iron-based
superconductors.Comment: 20 one-column pages with appendix, 9 figure
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