119 research outputs found
Filling-induced Mott transition and pseudogap physics in the triangular lattice Hubbard model
It has been reported that upon doping a Mott insulator, there can be a
crossover to a strongly correlated metallic phase followed by a first-order
transition to another thermodynamically stable metallic phase. We call this
first-order metal-metal transition the Sordi transition. To show theoretically
that this transition is observable, it is important to provide calculations in
situations where magnetic phase transitions do not hide the Sordi transition.
It is also important to show that it can be found on large clusters and with
different approaches. Here, we use the dynamical cluster approximation to
reveal the Sordi transition on a triangular lattice at finite temperature in
situations where there is no long-range magnetic correlations. This is relevant
for experiments on candidate spin-liquid organics. We also show that the
metallic phase closest to the insulator is a distinct pseudogap phase that
occurs because of strong interactions and short-range correlations
Mott transition, Widom line and pseudogap in the half-filled triangular lattice Hubbard model
The Mott transition is observed experimentally in materials that are
magnetically frustrated so that long-range order does not hide the Mott
transition at finite temperature. The Hubbard model on the triangular lattice
at half-filling is a paradigmatic model to study the interplay of interactions
and frustration on the normal-state phase diagram. We use the dynamical cluster
approximation with continuous time auxiliary field quantum Monte Carlo to solve
this model for 1, 4, 6, 12, and 16 site clusters with detailed analysis
performed for the 6 site cluster. We show that a) for every cluster there is an
inflection point in the double occupancy as a function of interaction, defining
a Widom line that extends above the critical point of the first-order Mott
transition; b) the presence of this line and the cluster size dependence argue
for the observability of the Mott transition at finite temperature in the
thermodynamic limit; c) the loss of spectral weight in the metal to Mott
insulator transition as a function of temperature and for strong interactions
is momentum dependent, the hallmark of a pseudogap. That pseudogap spans a
large region of the phase diagram near the Mott transition.Comment: Open source version of the published paper. 16 pages, 8 figures,
LaTe
Phylogeny of Prokaryotes and Chloroplasts Revealed by a Simple Composition Approach on All Protein Sequences from Complete Genomes Without Sequence Alignment
The complete genomes of living organisms have provided much information on their phylogenetic relationships. Similarly, the complete genomes of chloroplasts have helped to resolve the evolution of this organelle in photosynthetic eukaryotes. In this paper we propose an alternative method of phylogenetic analysis using compositional statistics for all protein sequences from complete genomes. This new method is conceptually simpler than and computationally as fast as the one proposed by Qi et al. (2004b) and Chu et al. (2004). The same data sets used in Qi et al. (2004b) and Chu et al. (2004) are analyzed using the new method. Our distance-based phylogenic tree of the 109 prokaryotes and eukaryotes agrees with the biologists tree of life based on 16S rRNA comparison in a predominant majority of basic branching and most lower taxa. Our phylogenetic analysis also shows that the chloroplast genomes are separated to two major clades corresponding to chlorophytes s.l. and rhodophytes s.l. The interrelationships among the chloroplasts are largely in agreement with the current understanding on chloroplast evolution
Characterization of an Ionization Readout Tile for nEXO
A new design for the anode of a time projection chamber, consisting of a
charge-detecting "tile", is investigated for use in large scale liquid xenon
detectors. The tile is produced by depositing 60 orthogonal metal
charge-collecting strips, 3~mm wide, on a 10~\si{\cm} 10~\si{\cm}
fused-silica wafer. These charge tiles may be employed by large detectors, such
as the proposed tonne-scale nEXO experiment to search for neutrinoless
double-beta decay. Modular by design, an array of tiles can cover a sizable
area. The width of each strip is small compared to the size of the tile, so a
Frisch grid is not required. A grid-less, tiled anode design is beneficial for
an experiment such as nEXO, where a wire tensioning support structure and
Frisch grid might contribute radioactive backgrounds and would have to be
designed to accommodate cycling to cryogenic temperatures. The segmented anode
also reduces some degeneracies in signal reconstruction that arise in
large-area crossed-wire time projection chambers. A prototype tile was tested
in a cell containing liquid xenon. Very good agreement is achieved between the
measured ionization spectrum of a Bi source and simulations that
include the microphysics of recombination in xenon and a detailed modeling of
the electrostatic field of the detector. An energy resolution =5.5\%
is observed at 570~\si{keV}, comparable to the best intrinsic ionization-only
resolution reported in literature for liquid xenon at 936~V/\si{cm}.Comment: 18 pages, 13 figures, as publishe
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