2,225 research outputs found
Higher-order topological insulators in amorphous solids
We identify the possibility of realizing higher order topological (HOT) phases in noncrystalline or amorphous materials. Starting from two- and three-dimensional crystalline HOT insulators, accommodating topological corner states, we gradually enhance structural randomness in the system. Within a parameter regime, as long as amorphousness is confined by an outer crystalline boundary, the system continues to host corner states, yielding amorphous HOT insulators. However, as structural disorder percolates to the edges, corner states start to dissolve into amorphous bulk, and ultimately the system becomes a trivial insulator when amorphousness plagues the entire system. These outcomes are further substantiated by computing the quadrupolar (octupolar) moment in two (three) dimensions. Therefore, HOT phases can be realized in amorphous solids, when wrapped by a thin (lithographically grown, for example) crystalline layer. Our findings suggest that crystalline topological phases can be realized even in the absence of local crystalline symmetry
Statistics-tuned phases of pseudofermions in one dimension
We show that a quadratic system of pseudofermions, with tunable
fractionalised statistics, can host a rich phase diagram on a one dimensional
chain with nearest and next nearest neighbor hopping. Using a combination of
numerical and analytical techniques, we show that that by varying the
statistical angle and the ratio of the hopping, the system stabilizes two
Tomonaga-Luttinger liquids (TLL) with central charges c = 1 and 2 respectively
along with the inversion symmetry broken bond ordered (BO) insulating phase.
Interestingly, the two quantum phase transitions in the system - (1) between
the two TLLs, and, (2) the c = 1 TLL and BO phase can be engendered by solely
tuning the statistics of the pseudofermions. Our analysis shows that both these
transition are continuous and novel with the former lacking a local
order-parameter based description and the latter of
Berezinskii-Kosterlitz-Thouless type. These phases and phase transitions can be
of direct experimental relevance in context of recent studies of fermionic cold
atoms.Comment: 6+12 pages, 4+14 figure
Level Density of a Bose Gas and Extreme Value Statistics
We establish a connection between the level density of a gas of
non-interacting bosons and the theory of extreme value statistics. Depending on
the exponent that characterizes the growth of the underlying single-particle
spectrum, we show that at a given excitation energy the limiting distribution
function for the number of excited particles follows the three universal
distribution laws of extreme value statistics, namely Gumbel, Weibull and
Fr\'echet. Implications of this result, as well as general properties of the
level density at different energies, are discussed.Comment: 4 pages, no figure
Calotes emma Gray, 1845 (Squamata: Agamidae): range extension and new addition to the reptilian fauna of Tripura, northeast India
Two new records of Calotes emma Gray, 1845, are reported from Srirampur and Homnpui in the state of Tripura, northeast India. These records are the first from Tripura. Present locality records extended the known distribution of C. emma in Southeast Asia.
Variation in butterfly diversity and unique species richness along different habitats in Trishna Wildlife Sanctuary, Tripura, northeast India
Quantification of butterfly diversity and species richness is of prime importance for evaluating the status of protected areas. Permanent line transect counts were used to record species richness and abundance of butterfly communities of different habitat types in Trishna wildlife sanctuary. A total of 1005 individuals representing 59 species in 48 genera belonging to five families were recorded in the present study. Of these, 23 species belonged to the family Nymphalidae and accounted for 38.98% of the total species and 45.20% of the total number of individuals. Mature secondary mixed moist deciduous forest showed the maximum diversity and species richness, while exotic grassland showed minimum diversity and species richness. Out of 59 species, 31 are new records for Tripura state, while 21 are unique species and nine are listed in the threatened category. This study revealed that mature secondary forests are more important for butterfly communities, while exotic grasslands have a negative impact on species composition
Resistivity due to a Domain Wall in Ferromagnetic Metal
The resistivity due to a domain wall in ferromagnetic metallic wire is
calculated based on the linear response theory. The interaction between
conduction electrons and the wall is expressed in terms of a classical gauge
field which is introduced by the local gauge transformation in the electron
spin space. It is shown that the wall contributes to the decoherence of
electrons and that this quantum correction can dominate over the Boltzmann
resisitivity, leading to a decrease of resisitivity by nucleation of a wall.
The conductance fluctuation due to the motion of the wall is also investigated.
The results are compared with recent experiments.Comment: 9 pages, 3 figure
X. couchianus and X. hellerii genome models provide genomic variation insight among Xiphophorus species
4 inter-chromosomal rearrangement events between X. hellerii and X. maculatus. (XLSX 40 kb
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