8,080 research outputs found
Pole expansion of self-energy and interaction effect on topological insulators
We study effect of interactions on time-reversal-invariant topological
insulators. Their topological indices are expressed by interacting Green's
functions. Under the local self-energy approximation, we connect topological
index and surface states of an interacting system to an auxiliary
noninteracting system, whose Hamiltonian is related to the pole-expansions of
the local self-energy. This finding greatly simplifies the calculation of
interacting topological indices and gives an noninteracting pictorial
description of interaction driven topological phase transitions. Our results
also bridge studies of the correlated topological insulating materials with the
practical dynamical-mean-field-theory calculations.Comment: 4.2 pages, 3 figures, reference added, typos correcte
Global Phase Diagram of Disordered Type-II Weyl Semimetals
With electron and hole pockets touching at the Weyl node, type-II Weyl
semimetal is a newly proposed topological state distinct from its type-I
cousin. We numerically study the localization effect for tilted type-I as well
as type-II Weyl semimetals and give the global phase diagram. For dis- ordered
type-I Weyl semimetal, an intermediate three-dimensional quantum anomalous Hall
phase is confirmed between Weyl semimetal phase and diffusive metal phase.
However, this intermediate phase is absent for disordered type-II Weyl
semimetal. Besides, near the Weyl nodes, comparing to its type-I cousin,
type-II Weyl semimetal possesses even larger ratio between the transport
lifetime along the direction of tilt and the quantum lifetime. Near the phase
boundary between the type-I and the type-II Weyl semimetals, infinitesimal
disorder will induce an insulating phase so that in this region, the concept of
Weyl semimetal is meaningless for real materials.Comment: 7 pages, 5 figure
Numerical Study of Universal Conductance Fluctuation in Three-dimensional Topological Semimetals
We study the conductance fluctuation in topological semimetals. Through
statistic distribution of energy levels of topological semimetals, we determine
the dominant parameters of universal conductance fluctuation (UCF), i.e., the
number of uncorrelated bands , the level degeneracy , and the symmetry
parameter . These parameters allow us to predict the zero-temperature
intrinsic UCF of topological semimetals by the Altshuler-Lee-Stone theory.
Then, we obtain numerically the conductance fluctuations for topological
semimetals of quasi-1D geometry. We find that for Dirac/Weyl semimetals, the
theoretical prediction coincides with the numerical results. However, a
non-universal conductance fluctuation behavior is found for topological nodal
line semimetals, i.e., the conductance fluctuation amplitude increases with the
enlargement of SOC strength. We find that such unexpected parameter-dependent
phenomena of conductance fluctuation are related to Fermi surface shape of 3D
topological semimetals. These results will help us to understand the existing
and future experimental results of UCF in 3D topological semimetals.Comment: 9 pages, 8 figure
Predicting species' tolerance to salinity and alkalinity using distribution data and geochemical modelling: a case study using Australian grasses
BACKGROUND AND AIMS: Salt tolerance has evolved many times independently in different plant groups. One possible explanation for this pattern is that it builds upon a general suite of stress-tolerance traits. If this is the case, then we might expect a correlation between salt tolerance and other tolerances to different environmental stresses. This association has been hypothesized for salt and alkalinity tolerance. However, a major limitation in investigating large-scale patterns of these tolerances is that lists of known tolerant species are incomplete. This study explores whether species' salt and alkalinity tolerance can be predicted using geochemical modelling for Australian grasses. The correlation between taxa found in conditions of high predicted salinity and alkalinity is then assessed. METHODS: Extensive occurrence data for Australian grasses is used together with geochemical modelling to predict values of pH and electrical conductivity to which species are exposed in their natural distributions. Using parametric and phylogeny-corrected tests, the geochemical predictions are evaluated using a list of known halophytes as a control, and it is determined whether taxa that occur in conditions of high predicted salinity are also found in conditions of high predicted alkalinity. KEY RESULTS: It is shown that genera containing known halophytes have higher predicted salinity conditions than those not containing known halophytes. Additionally, taxa occurring in high predicted salinity tend to also occur in high predicted alkalinity. CONCLUSIONS: Geochemical modelling using species' occurrence data is a potentially useful approach to predict species' relative natural tolerance to challenging environmental conditions. The findings also demonstrate a correlation between salinity tolerance and alkalinity tolerance. Further investigations can consider the phylogenetic distribution of specific traits involved in these ecophysiological strategies, ideally by incorporating more complete, finer-scale geochemical information, as well as laboratory experiments.This work was supported by the Australian Research Council
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