561 research outputs found
Exact Chiral Spin Liquids and Mean-Field Perturbations of Gamma Matrix Models on the Ruby Lattice
We theoretically study an exactly solvable Gamma matrix generalization of the
Kitaev spin model on the ruby lattice, which is a honeycomb lattice with
"expanded" vertices and links. We find this model displays an exceptionally
rich phase diagram that includes: (i) gapless phases with stable spin fermi
surfaces, (ii) gapless phases with low-energy Dirac cones and quadratic band
touching points, and (iii) gapped phases with finite Chern numbers possessing
the values {\pm}4,{\pm}3,{\pm}2 and {\pm}1. The model is then generalized to
include Ising-like interactions that break the exact solvability of the model
in a controlled manner. When these terms are dominant, they lead to a trivial
Ising ordered phase which is shown to be adiabatically connected to a large
coupling limit of the exactly solvable phase. In the limit when these
interactions are weak, we treat them within mean-field theory and present the
resulting phase diagrams. We discuss the nature of the transitions between
various phases. Our results highlight the richness of possible ground states in
closely related magnetic systems.Comment: 9 pages, 9 figure
Kaleidoscope of topological phases with multiple Majorana species
Exactly solvable lattice models for spins and non-interacting fermions
provide fascinating examples of topological phases, some of them exhibiting the
localized Majorana fermions that feature in proposals for topological quantum
computing. The Chern invariant is one important characterization of such
phases. Here we look at the square-octagon variant of Kitaev's honeycomb model.
It maps to spinful paired fermions and enjoys a rich phase diagram featuring
distinct abelian and nonabelian phases with and . The and phases all support localized Majorana
modes and are examples of Ising and anyon theories respectively.Comment: 6 pages, 5 figures. The second version has a new title, reflecting a
change of focus of the presentation in this version. The third version
contains minor changes and is essentially the one published in New Journal of
Physic
M\"ossbauer Antineutrinos: Recoilless Resonant Emission and Absorption of Electron Antineutrinos
Basic questions concerning phononless resonant capture of monoenergetic
electron antineutrinos (M\"ossbauer antineutrinos) emitted in bound-state
beta-decay in the 3H - 3He system are discussed. It is shown that lattice
expansion and contraction after the transformation of the nucleus will
drastically reduce the probability of phononless transitions and that various
solid-state effects will cause large line broadening. As a possible
alternative, the rare-earth system 163Ho - 163Dy is favoured.
M\"ossbauer-antineutrino experiments could be used to gain new and deep
insights into several basic problems in neutrino physics
Zero-voltage conductance peak from weak antilocalization in a Majorana nanowire
We show that weak antilocalization by disorder competes with resonant Andreev
reflection from a Majorana zero-mode to produce a zero-voltage conductance peak
of order e^2/h in a superconducting nanowire. The phase conjugation needed for
quantum interference to survive a disorder average is provided by particle-hole
symmetry - in the absence of time-reversal symmetry and without requiring a
topologically nontrivial phase. We identify methods to distinguish the Majorana
resonance from the weak antilocalization effect.Comment: 13 pages, 8 figures. Addendum, February 2014: Appendix B shows
results for weak antilocalization in the circular ensemble. (This appendix is
not in the published version.
Stability of corn (\u3ci\u3eZea mays\u3c/i\u3e)- foxtail (\u3ci\u3eSetaria\u3c/i\u3e spp.) interference relationships
Variation in interference relationships have been shown for a number of crop-weed associations and may have an important effect on the implementation of decision support systems for weed management. Multiyear field experiments were conducted at eight locations to determine the stability of corn-foxtail interference relationships across years and locations. Two coefficients (I and A) of a rectangular hyperbola equation were estimated for each data set using nonlinear regression procedures. The I and A coefficients represent percent corn yield loss as foxtail density approaches zero and maximum percent corn yield loss, respectively. The coefficient I was stable across years at two locations and varied across years at four locations. Maximum yield loss (A) varied between years at one location. Both coefficients varied among locations. Although 3 to 4 foxtail plants m-1 row was a conservative estimate of the single-year economic threshold (Te) of foxtail density, variation in I and A resulted in a large variation in Te. Therefore, the utility of using common coefficient estimates to predict future crop yield loss from foxtail interference between years or among locations within a region is limited
Stability of corn (\u3ci\u3eZea mays\u3c/i\u3e)- foxtail (\u3ci\u3eSetaria\u3c/i\u3e spp.) interference relationships
Variation in interference relationships have been shown for a number of crop-weed associations and may have an important effect on the implementation of decision support systems for weed management. Multiyear field experiments were conducted at eight locations to determine the stability of corn-foxtail interference relationships across years and locations. Two coefficients (I and A) of a rectangular hyperbola equation were estimated for each data set using nonlinear regression procedures. The I and A coefficients represent percent corn yield loss as foxtail density approaches zero and maximum percent corn yield loss, respectively. The coefficient I was stable across years at two locations and varied across years at four locations. Maximum yield loss (A) varied between years at one location. Both coefficients varied among locations. Although 3 to 4 foxtail plants m-1 row was a conservative estimate of the single-year economic threshold (Te) of foxtail density, variation in I and A resulted in a large variation in Te. Therefore, the utility of using common coefficient estimates to predict future crop yield loss from foxtail interference between years or among locations within a region is limited
Lock acquisition of a gravitational-wave interferometer
Interferometric gravitational-wave detectors, such as the Laser Interferometer Gravitational Wave Observatory (LIGO) detectors currently under construction, are based on kilometer-scale Michelson interferometers, with sensitivity that is enhanced by addition of multiple coupled optical resonators. Reducing the relative optic motions to bring the system to the resonant operating point is a significant challenge. We present a new approach to lock acquisition, used to lock a LIGO interferometer, whereby the sensor transformation matrix is dynamically calculated to sequentially bring the cavities into resonance
Upper Limits on a Stochastic Background of Gravitational Waves
The Laser Interferometer Gravitational-Wave Observatory has performed a third science run with much improved sensitivities of all three interferometers. We present an analysis of approximately 200 hours of data acquired during this run, used to search for a stochastic background of gravitational radiation. We place upper bounds on the energy density stored as gravitational radiation for three different spectral power laws. For the flat spectrum, our limit of Ω_0<8.4×10^(-4) in the 69–156 Hz band is ~10^5 times lower than the previous result in this frequency range
- …