47 research outputs found
Quantum Criticality and Novel Phases: Summary and Outlook
This conference summary and outlook provides a personal overview of the
topics and themes of the August 2009 Dresden meeting on quantum criticality and
novel phases. The dichotomy between the local moment and the itinerant views of
magnetism is revisited and refreshed in new materials, new probes and new
theoretical ideas. New universality and apparent zero temperature phases of
matter move us beyond the old ideas of quantum criticality. This is accompanied
by alternative pairing interactions and as yet unidentified phases developing
in the vicinity of quantum critical points. In discussing novel order, the
magnetic analogues of superconductivity are considered as candidate states for
the hidden order that sometimes develops in the vicinity of quantum critical
points in metallic systems. These analogues can be thought of as "pairing" in
the particle-hole channel and are tabulated. This analogy is used to outline a
framework to study the relation between ferromagnetic fluctuations and the
propensity of a metal to nematic type phases which at weak coupling correspond
to Pomeranchuk instabilities. This question can be related to the fundamental
relations of Fermi liquid theory.Comment: Conference summary for the 2009 Dresden Meeting on Quantum
Criticality and Novel Phases. 7 pages and 4 figures. The associated
presentation may be found at
http://www.theory.bham.ac.uk/staff/schofield/talks/Dresden
A linear, second-order, energy stable, fully adaptive finite-element method for phase-field modeling of wetting phenomena
We propose a new numerical method to solve the Cahn-Hilliard equation coupled with non-linear wetting boundary conditions. We show that the method is mass-conservative and that the discrete solution satisfies a discrete energy law similar to the one satisfied by the exact solution. We perform several tests inspired by realistic situations to verify the accuracy and performance of the method: wetting of a chemically heterogeneous substrate in three dimensions, wetting-driven nucleation in a complex two dimensional domain and three-dimensional diffusion through a porous medium
Flux Phase as a Dynamic Jahn-Teller Phase: Berryonic Matter in the Cuprates?
There is considerable evidence for some form of charge ordering on the
hole-doped stripes in the cuprates, mainly associated with the low-temperature
tetragonal phase, but with some evidence for either charge density waves or a
flux phase, which is a form of dynamic charge-density wave. These three states
form a pseudospin triplet, demonstrating a close connection with the E X e
dynamic Jahn-Teller effect, suggesting that the cuprates constitute a form of
Berryonic matter. This in turn suggests a new model for the dynamic Jahn-Teller
effect as a form of flux phase. A simple model of the Cu-O bond stretching
phonons allows an estimate of electron-phonon coupling for these modes,
explaining why the half breathing mode softens so much more than the full
oxygen breathing mode. The anomalous properties of provide a coupling
(correlated hopping) which acts to stabilize density wave phases.Comment: Major Revisions: includes comparisons with specific cuprate phonon
modes, 16 eps figures, revte
BLOOM: A 176B-Parameter Open-Access Multilingual Language Model
Large language models (LLMs) have been shown to be able to perform new tasks
based on a few demonstrations or natural language instructions. While these
capabilities have led to widespread adoption, most LLMs are developed by
resource-rich organizations and are frequently kept from the public. As a step
towards democratizing this powerful technology, we present BLOOM, a
176B-parameter open-access language model designed and built thanks to a
collaboration of hundreds of researchers. BLOOM is a decoder-only Transformer
language model that was trained on the ROOTS corpus, a dataset comprising
hundreds of sources in 46 natural and 13 programming languages (59 in total).
We find that BLOOM achieves competitive performance on a wide variety of
benchmarks, with stronger results after undergoing multitask prompted
finetuning. To facilitate future research and applications using LLMs, we
publicly release our models and code under the Responsible AI License
Resonance states of superheavy hydrogen nuclei obtained in transfer reactions with exotic beams
A resonance state situated at 1.8 +/- 0.1 and, most likely, another state positioned at 2.7 +/- 0.1 MeV above the t+n+n decay threshold were observed in the missing mass energy spectrum of the H-5 nucleus produced in the reaction H-3(t,p)H-5. The peak located close to E-5H = 1.8 MeV also was seen in the H-5 spectrum obtained from the energy distributions of 3H nuclei emitted in the reaction H-2(He-6,H-5)He-3. The width (Gamma(obs) less than or equal to 0.5 MeV) obtained for the two 5H resonance states is surprisingly small. A state of H-4 with E-res = 3.3 MeV and gamma(2) = 2.3 MeV was obtained in the reaction H-2(t,p)H-4 from the proton spectrum
Two energy scales in the spin excitations of the high-temperature superconductor La2-xSrxCuO4
The excitations responsible for producing high-temperature superconductivity
in the cuprates have not been identified. Two promising candidates are
collective spin excitations and phonons. A recent argument against spin
excitations has been their inability to explain structures seen in electronic
spectroscopies such as photoemission and tunnelling. Here we use inelastic
neutron scattering to demonstrate that collective spin excitations in optimally
doped LaSrCuO are more structured than previously thought.
The excitations have a two component structure with a low-frequency component
strongest around 18 meV and a broader component strongest near 40-70 meV. The
second component carries most of the spectral weight and its energy matches
structure seen in photoemission and tunnelling spectra in the range 50-90 meV.
Our results demonstrate that collective spin excitations can explain features
of quasiparticle spectroscopies and are therefore likely to be the strongest
coupled excitations.Comment: accepted for publication in Nature Physics, original submissio