33 research outputs found
Emergent SU(N) symmetry in disordered SO(N) spin chains
Strongly disordered spin chains invariant under the SO(N) group are shown to
display random-singlet phases with emergent SU(N) symmetry without fine tuning.
The phases with emergent SU(N) symmetry are of two kinds: one has a ground
state formed of randomly distributed singlets of strongly bound pairs of SO(N)
spins (a `mesonic' phase), while the other has a ground state composed of
singlets made out of strongly bound integer multiples of N SO(N) spins (a
`baryonic' phase). The established mechanism is general and we put forward the
cases of and as prime candidates for experimental
realizations in material compounds and cold-atoms systems. We display universal
temperature scaling and critical exponents for susceptibilities distinguishing
these phases and characterizing the enlarging of the microscopic symmetries at
low energies.Comment: 5 pages, 2 figures, Contribution to the Topical Issue "Recent
Advances in the Theory of Disordered Systems", edited by Ferenc Igl\'oi and
Heiko Riege
Highly-symmetric random one-dimensional spin models
The interplay of disorder and interactions is a challenging topic of
condensed matter physics, where correlations are crucial and exotic phases
develop. In one spatial dimension, a particularly successful method to analyze
such problems is the strong-disorder renormalization group (SDRG). This method,
which is asymptotically exact in the limit of large disorder, has been
successfully employed in the study of several phases of random magnetic chains.
Here we develop an SDRG scheme capable to provide in-depth information on a
large class of strongly disordered one-dimensional magnetic chains with a
global invariance under a generic continuous group. Our methodology can be
applied to any Lie-algebra valued spin Hamiltonian, in any representation. As
examples, we focus on the physically relevant cases of SO(N) and Sp(N)
magnetism, showing the existence of different randomness-dominated phases.
These phases display emergent SU(N) symmetry at low energies and fall in two
distinct classes, with meson-like or baryon-like characteristics. Our
methodology is here explained in detail and helps to shed light on a general
mechanism for symmetry emergence in disordered systems.Comment: 26 pages, 12 figure
Origin of the butterfly magnetoresistance in a Dirac nodal-line system
We report a study on the magnetotransport properties and on the Fermi
surfaces (FS) of the ZrSi(Se,Te) semimetals. Density Functional Theory (DFT)
calculations, in absence of spin orbit coupling (SOC), reveal that both the Se
and the Te compounds display Dirac nodal lines (DNL) close to the Fermi level
at symmorphic and non-symmorphic positions, respectively. We
find that the geometry of their FSs agrees well with DFT predictions. ZrSiSe
displays low residual resistivities, pronounced magnetoresistivity, high
carrier mobilities, and a butterfly-like angle-dependent magnetoresistivity
(AMR), although its DNL is not protected against gap opening. As in
CdAs, its transport lifetime is found to be 10 to 10 times
larger than its quantum one. ZrSiTe, which possesses a protected DNL, displays
conventional transport properties. Our evaluation indicates that both compounds
most likely are topologically trivial. Nearly angle-independent effective
masses with strong angle dependent quantum lifetimes lead to the butterfly AMR
in ZrSiSe
The Genetics and Genomics of Virus Resistance in Maize
Viruses cause significant diseases on maize worldwide. Intensive agronomic practices, changes in vector distribution, and the introduction of vectors and viruses into new areas can result in emerging disease problems. Because deployment of resistant hybrids and cultivars is considered to be both economically viable and environmentally sustainable, genes and quantitative trait loci for most economically important virus diseases have been identified. Examination of multiple studies indicates the importance of regions of maize chromosomes 2, 3, 6, and 10 in virus resistance. An understanding of the molecular basis of virus resistance in maize is beginning to emerge, and two genes conferring resistance to sugarcane mosaic virus, Scmv1 and Scmv2, have been cloned and characterized. Recent studies provide hints of other pathways and genes critical to virus resistance in maize, but further work is required to determine the roles of these in virus susceptibility and resistance. This research will be facilitated by rapidly advancing technologies for functional analysis of genes in maize
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