558 research outputs found
Resonating color state and emergent chromodynamics in the kagome antiferromagnet
We argue that the spin-wave breakdown in the Heisenberg kagome
antiferromagnet signals an instability of the ground state and leads, through
an emergent local constraint, to a quantum dynamics described by a gauge theory
similar to that of chromodynamics. For integer spins, we show that the quantum
fluctuations of the gauge modes select the sqrt(3)xsqrt(3) Neel state with an
on-site moment renormalized by color resonances. We find non-magnetic
low-energy excitations that may be responsible for a deconfinement "transition"
at experimentally accessible temperatures which we estimate.Comment: 4 pages, 4 figures, v2: printable figs, v3: publ. versio
Signatures of a gearwheel quantum spin liquid in a spin- pyrochlore molybdate Heisenberg antiferromagnet
We theoretically investigate the low-temperature phase of the recently
synthesized LuMoON material, an extraordinarily rare
realization of a three-dimensional pyrochlore Heisenberg
antiferromagnet in which Mo are the magnetic species. Despite a
Curie-Weiss temperature () of K, experiments have
found no signature of magnetic ordering spin freezing down to
K. Using density functional theory, we find that the compound
is well described by a Heisenberg model with exchange parameters up to third
nearest neighbors. The analysis of this model via the pseudofermion functional
renormalization group method reveals paramagnetic behavior down to a
temperature of at least , in agreement with the
experimental findings hinting at a possible three-dimensional quantum spin
liquid. The spin susceptibility profile in reciprocal space shows
momentum-dependent features forming a "gearwheel" pattern, characterizing what
may be viewed as a molten version of a chiral noncoplanar incommensurate spiral
order under the action of quantum fluctuations. Our calculated reciprocal space
susceptibility maps provide benchmarks for future neutron scattering
experiments on single crystals of LuMoON.Comment: Published version. Main paper (6 pages, 3 figures) + Supplemental
Material (4 pages, 3 figures, 1 table
Ydj1 governs fungal morphogenesis and stress response, and facilitates mitochondrial protein import via Mas1 and Mas2
We thank Zhen-Yuan Lin for help in the preparation of the AP-MS samples, and Cathy Collins for technical assistance. MDL is supported by a Sir Henry Wellcome Postdoctoral Fellowship (Wellcome Trust 096072), LEC is supported by a Canada Research Chair in Microbial Genomics and Infectious Disease and by Cana-dian Institutes of Health Research (CIHR) Grants MOP-119520 and MOP-86452. OK is supported by National Insti-tutes of Health grant 5R01GM108975. A-CG is supported by a CIHR Foundation Grant (FDN143301), Genome Cana-da Genomics Innovation Network (GIN) Node and Tech-nical Development Grants, and a Canada Research Chair in Functional Proteomics. J-PL was supported by a TD Bank Health Research Fellowship at the Lunenfeld-Tanenbaum Research Institute and by a Scholarship for the Next Gen-eration of Scientists from the Cancer Research Society. JLX is supported by a CIHR – Frederick Banting and Charles Best Canada Graduate Scholarship. The funding agencies had no role in the study design, data collection and inter-pretation, or the decision to submit the work for publication.Peer reviewedPublisher PD
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
Artificial Kagome Arrays of Nanomagnets: A Frozen Dipolar Spin Ice
Magnetic frustration effects in artificial kagome arrays of nanomagnets are
investigated using x-ray photoemission electron microscopy and Monte Carlo
simulations. Spin configurations of demagnetized networks reveal unambiguous
signatures of long range, dipolar interaction between the nanomagnets. As soon
as the system enters the spin ice manifold, the kagome dipolar spin ice model
captures the observed physics, while the short range kagome spin ice model
fails.Comment: 4 pages, 4 figures, 1 tabl
Quantum spin fluctuations in the dipolar Heisenberg-like rare earth pyrochlores
The magnetic pyrochlore oxide materials of general chemical formula R2Ti2O7
and R2Sn2O7 (R = rare earth) display a host of interesting physical behaviours
depending on the flavour of rare earth ion. These properties depend on the
value of the total magnetic moment, the crystal field interactions at each rare
earth site and the complex interplay between magnetic exchange and long-range
dipole-dipole interactions. This work focuses on the low temperature physics of
the dipolar isotropic frustrated antiferromagnetic pyrochlore materials.
Candidate magnetic ground states are numerically determined at zero temperature
and the role of quantum spin fluctuations around these states are studied using
a Holstein-Primakoff spin wave expansion to order 1/S. The results indicate the
strong stability of the proposed classical ground states against quantum
fluctuations. The inclusion of long range dipole interactions causes a
restoration of symmetry and a suppression of the observed anisotropy gap
leading to an increase in quantum fluctuations in the ground state when
compared to a model with truncated dipole interactions. The system retains most
of its classical character and there is little deviation from the fully ordered
moment at zero temperature.Comment: Latex2e, 18 pages, 4 figures, IOP forma
Evaluation of mTOR-regulated mRNA translation.
mTOR, the mammalian target of rapamycin, regulates protein synthesis (mRNA translation) by affecting the phosphorylation or activity of several translation factors. Here, we describe methods for studying the impact of mTOR signalling on protein synthesis, using inhibitors of mTOR such as rapamycin (which impairs some of its functions) or mTOR kinase inhibitors (which probably block all functions).To assess effects of mTOR inhibition on general protein synthesis in cells, the incorporation of radiolabelled amino acids into protein is measured. This does not yield information on the effects of mTOR on the synthesis of specific proteins. To do this, two methods are described. In one, stable-isotope labelled amino acids are used, and their incorporation into new proteins is determined using mass spectrometric methods. The proportions of labelled vs. unlabeled versions of each peptide from a given protein provide quantitative information about the rate of that protein's synthesis under different conditions. Actively translated mRNAs are associated with ribosomes in polyribosomes (polysomes); thus, examining which mRNAs are found in polysomes under different conditions provides information on the translation of specific mRNAs under different conditions. A method for the separation of polysomes from non-polysomal mRNAs is describe
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