75 research outputs found
The overdoped end of the cuprate phase diagram
Studying the disappearance of superconductivity at the end of the overdoped
region of the cuprate phase diagram offers a different approach for
investigating the interaction which is responsible for pairing in these
materials. In the underdoped region this question is complicated by the
presence of charge and stripe ordered phases as well as the pseudogap. In the
overdoped region the situation appears simpler with only a normal phase, a
superconducting phase and impurity scattering. Here, for the overdoped region,
we report the results of a combined dynamic cluster approximation (DCA) and a
weak Born impurity scattering calculation for a Hubbard model. We find
that a decrease in the -wave pairing strength of the two-particle scattering
vertex is closely coupled to changes in the momentum and frequency structure of
the magnetic spin fluctuations as the system is overdoped. Treating the
impurity scattering within a disordered BCS -wave approximation, we see how
the combined effects of the decreasing -wave pairing strength and weak
impurity scattering lead to the end of the dome.Comment: 5 pages, 5 figure
Control of the properties of micro-structured waveguides in lithium niobate crystal
We study numerically depressed-cladding, buried waveguides that can be formed in a lithium niobate crystal by femtosecond laser writing. We demonstrate that the guiding properties can be controlled by the waveguide structural characteristics
Robust charge-density wave correlations in the electron-doped single-band Hubbard model
There is growing evidence that the hole-doped single-band Hubbard and -
models do not have a superconducting ground state reflective of the
high-temperature cuprate superconductors but instead have striped spin- and
charge-ordered ground states. Nevertheless, it is proposed that these models
may still provide an effective low-energy model for electron-doped materials.
Here we study the finite temperature spin and charge correlations in the
electron-doped Hubbard model using quantum Monte Carlo dynamical cluster
approximation calculations and contrast their behavior with those found on the
hole-doped side of the phase diagram. We find evidence for a charge modulation
with both checkerboard and unidirectional components decoupled from any
spin-density modulations. These correlations are inconsistent with a
weak-coupling description based on Fermi surface nesting, and their doping
dependence agrees qualitatively with resonant inelastic x-ray scattering
measurements. Our results provide evidence that the single-band Hubbard model
describes the electron-doped cuprates
Magnetism and Metallicity in Moir\'e Transition Metal Dichalcogenides
The ability to control the properties of twisted bilayer transition metal
dichalcogenides in situ makes them an ideal platform for investigating the
interplay of strong correlations and geometric frustration. Of particular
interest are the low energy scales, which make it possible to experimentally
access both temperature and magnetic fields that are of the order of the
bandwidth or the correlation scale. In this manuscript we analyze the moir\'e
Hubbard model, believed to describe the low energy physics of an important
subclass of the twisted bilayer compounds. We establish its magnetic and the
metal-insulator phase diagram for the full range of magnetic fields up to the
fully spin polarized state. We find a rich phase diagram including fully and
partially polarized insulating and metallic phases of which we determine the
interplay of magnetic order, Zeeman-field, and metallicity, and make connection
to recent experiments.Comment: 7 (+9) pages, 4 (+8) figure
Redox-dependent and redox-independent functions of Caenorhabditis elegans thioredoxin 1
Thioredoxins (TRX) are traditionally considered as enzymes catalyzing redox reactions. However, redox-independent functions of thioredoxins have been described in different organisms, although the underlying molecular mechanisms are yet unknown. We report here the characterization of the first generated endogenous redox-inactive thioredoxin in an animal model, the TRX-1 in the nematode Caenorhabditis elegans. We find that TRX-1 dually regulates the formation of an endurance larval stage (dauer) by interacting with the insulin pathway in a redox-independent manner and the cGMP pathway in a redox-dependent manner. Moreover, the requirement of TRX-1 for the extended longevity of worms with compromised insulin signalling or under calorie restriction relies on TRX-1 redox activity. In contrast, the nuclear translocation of the SKN-1 transcription factor and increased LIPS-6 protein levels in the intestine upon trx-1 deficiency are strictly redox-independent. Finally, we identify a novel function of C. elegans TRX-1 in male food-leaving behaviour that is redox-dependent. Taken together, our results position C. elegans as an ideal model to gain mechanistic insight into the redox-independent functions of metazoan thioredoxins, overcoming the limitations imposed by the embryonic lethal phenotypes of thioredoxin mutants in higher organisms
Evolution of spin excitations from bulk to monolayer FeSe
In ultrathin films of FeSe grown on SrTiO (FeSe/STO), the superconducting transition temperature T is increased by almost an order of magnitude, raising questions on the pairing mechanism. As in other superconductors, antiferromagnetic spin fluctuations have been proposed to mediate SC making it essential to study the evolution of the spin dynamics of FeSe from the bulk to the ultrathin limit. Here, we investigate the spin excitations in bulk and monolayer FeSe/STO using resonant inelastic x-ray scattering (RIXS) and quantum Monte Carlo (QMC) calculations. Despite the absence of long-range magnetic order, bulk FeSe displays dispersive magnetic excitations reminiscent of other Fe-pnictides. Conversely, the spin excitations in FeSe/STO are gapped, dispersionless, and significantly hardened relative to its bulk counterpart. By comparing our RIXS results with simulations of a bilayer Hubbard model, we connect the evolution of the spin excitations to the Fermiology of the two systems revealing a remarkable reconfiguration of spin excitations in FeSe/STO, essential to understand the role of spin fluctuations in the pairing mechanism
Phase diagram of the two-dimensional Hubbard-Holstein model
The electron\u2013electron and electron\u2013phonon interactions play an important role in correlated materials, being key features for spin, charge and pair correlations. Thus, here we investigate their effects in strongly correlated systems by performing unbiased quantum Monte Carlo simulations in the square lattice Hubbard-Holstein model at half-filling. We study the competition and interplay between antiferromagnetism (AFM) and charge-density wave (CDW), establishing its very rich phase diagram. In the region between AFM and CDW phases, we have found an enhancement of superconducting pairing correlations, favouring (nonlocal) s-wave pairs. Our study sheds light over past inconsistencies in the literature, in particular the emergence of CDW in the pure Holstein model case
Centering inclusivity in the design of online conferences: An OHBM-Open Science perspective
As the global health crisis unfolded, many academic conferences moved online in 2020. This move has been hailed as a positive step towards inclusivity in its attenuation of economic, physical, and legal barriers and effectively enabled many individuals from groups that have traditionally been underrepresented to join and participate. A number of studies have outlined how moving online made it possible to gather a more global community and has increased opportunities for individuals with various constraints, e.g., caregiving responsibilities. Yet, the mere existence of online conferences is no guarantee that everyone can attend and participate meaningfully. In fact, many elements of an online conference are still significant barriers to truly diverse participation: the tools used can be inaccessible for some individuals; the scheduling choices can favour some geographical locations; the set-up of the conference can provide more visibility to well-established researchers and reduce opportunities for early-career researchers. While acknowledging the benefits of an online setting, especially for individuals who have traditionally been underrepresented or excluded, we recognize that fostering social justice requires inclusivity to actively be centered in every aspect of online conference design. Here, we draw from the literature and from our own experiences to identify practices that purposefully encourage a diverse community to attend, participate in, and lead online conferences. Reflecting on how to design more inclusive online events is especially important as multiple scientific organizations have announced that they will continue offering an online version of their event when in-person conferences can resume
The past, present, and future of the Brain Imaging Data Structure (BIDS)
The Brain Imaging Data Structure (BIDS) is a community-driven standard for the organization of
data and metadata from a growing range of neuroscience modalities. This paper is meant as a
history of how the standard has developed and grown over time. We outline the principles
behind the project, the mechanisms by which it has been extended, and some of the challenges
being addressed as it evolves. We also discuss the lessons learned through the project, with the
aim of enabling researchers in other domains to learn from the success of BIDS
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