11,336 research outputs found
Spontaneous symmetry breaking and quantum Hall valley ordering on the surface of topological hexaborides
A number of strongly correlated heavy fermion compounds, such as samarium
(Sm), ytterbium (Yb), plutonium (Pu) hexaboride, are predicted to become
topological insulators at low temperatures. These systems support massless
Dirac fermions near certain (three) points of the surface Brillouin zone,
hereafter referred to as the valleys. In strong perpendicular magnetic fields,
the conical Dirac dispersions of these surface states quench onto three sets of
Landau levels and we predict various possible hierarchies of incompressible
quantum Hall states on the surface of hexaborides. In addition, we address the
effects of strong electron-electron interaction within the surface zeroth
Landau levels. Specifically, we show that depending on the relative strength of
the long-range (Coulomb-type) and the finite-range (Hubbard-type) interactions
the ground state can display either a valley-polarized or a valley-coherent
distribution of electronic density. We also show that the transition between
two valley-polarized states is always discontinuous, while that between a
valley-polarized and a valley-coherent phase is continuous. The Zeeman
splitting and/or an applied uniaxial strain on the surface can drive the system
through various quantum phase transitions and place it in different
broken-symmetry phases. Application of uniaxial strain is also shown to
considerably modify the precise sequence of quantum Hall states. We also
highlight the role of topology in determining the broken symmetry phases,
disorder on the surface of topological hexaborides in strong magnetic fields.Comment: 14 pages, 7 figure
Unconventional Fusion and Braiding of Topological Defects in a Lattice Model
We demonstrate the semiclassical nature of symmetry twist defects that differ
from quantum deconfined anyons in a true topological phase by examining
non-abelian crystalline defects in an abelian lattice model. An underlying
non-dynamical ungauged S3-symmetry labels the quasi-extensive defects by group
elements and gives rise to order dependent fusion. A central subgroup of local
Wilson observables distinguishes defect-anyon composites by species, which can
mutate through abelian anyon tunneling by tuning local defect phase parameters.
We compute a complete consistent set of primitive basis transformations, or
F-symbols, and study braiding and exchange between commuting defects. This
suggests a modified spin-statistics theorem for defects and non-modular group
structures unitarily represented by the braiding S and exchange T matrices.
Non-abelian braiding operations in a closed system represent the sphere braid
group projectively by a non-trivial central extension that relates the
underlying symmetry.Comment: 44 pages, 43 figure
Braiding Statistics and Congruent Invariance of Twist Defects in Bosonic Bilayer Fractional Quantum Hall States
We describe the braiding statistics of topological twist defects in abelian
bosonic bilayer (mmn) fractional quantum Hall (FQH) states, which reduce to the
Z_n toric code when m=0. Twist defects carry non-abelian fractional
Majorana-like characteristics. We propose local statistical measurements that
distinguish the fractional charge, or species, of a defect-quasiparticle
composite. Degenerate ground states and basis transformations of a multi-defect
system are characterized by a consistent set of fusion properties. Non-abelian
unitary exchange operations are determined using half braids between defects,
and projectively represent the sphere braid group in a closed system. Defect
spin statistics are modified by equating exchange with 4\pi rotation. The
braiding S matrix is identified with a Dehn twist (instead of a \pi/2 rotation)
on a torus decorated with a non-trivial twofold branch cut, and represents the
congruent subgroup \Gamma_0(2) of modular transformations.Comment: 6 pages, 3 figure
From orbifolding conformal field theories to gauging topological phases
Topological phases of matter in (2+1) dimensions are commonly equipped with
global symmetries, such as electric-magnetic duality in gauge theories and
bilayer symmetry in fractional quantum Hall states. Gauging these symmetries
into local dynamical ones is one way of obtaining exotic phases from
conventional systems. We study this using the bulk-boundary correspondence and
applying the orbifold construction to the (1+1) dimensional edge described by a
conformal field theory (CFT). Our procedure puts twisted boundary conditions
into the partition function, and predicts the fusion, spin and braiding
behavior of anyonic excitations after gauging. We demonstrate this for the
electric-magnetic self-dual gauge theory, the twofold symmetric
, and the -symmetric Wess-Zumino-Witten theories.Comment: 23 pages, 1 figur
Does reduced usage of antibiotics in livestock production mitigate the spread of antibiotic resistance in soil, earthworm guts, and the phyllosphere?
The overuse of antibiotics in animal husbandry is widespread and believed to significantly contribute to the selection of antibiotic resistance genes (ARGs) in animals. Thus, there is a global drive to reduce antibiotic use in the agricultural sector. However, it has not been established whether a reduction in the use of antibiotics in livestock production would be effective in reducing the spread of ARGs. A microcosm approach was used to determine how the addition of manure with either reduced antibiotic levels or with typical antibiotic levels could affect the spread of antibiotic resistance genes between soil, earthworms and the phyllosphere. When compared to the control soil, earthworm and phyllosphere samples had the greater increase in ARG abundance in conventional manure treatments (P < 0.05). Reduced antibiotic manure also enriched the abundance of ARGs in the phyllosphere and soil but not earthworm guts when compared to the control (P < 0.05). In both soil and earthworm guts, the enrichment of ARGs was lower in reduced antibiotic manure than in conventional manure. This study has identified bacterial transfer through the soil-earthworm-phyllosphere system as a potential means to spread ARGs between habitats after fertilization with livestock derived manures
Multivariate Operator-Self-Similar Random Fields
Multivariate random fields whose distributions are invariant under
operator-scalings in both time-domain and state space are studied. Such random
fields are called operator-self-similar random fields and their scaling
operators are characterized. Two classes of operator-self-similar stable random
fields with values in are constructed by
utilizing homogeneous functions and stochastic integral representations.Comment: 27 page
- …