18,158 research outputs found
Unusual persistence of superconductivity against high magnetic fields in the strongly-correlated iron-chalcogenide film FeTe:O
We report an unusual persistence of superconductivity against high magnetic
fields in the iron chalcogenide film FeTe:O below ~ 2.5 K. Instead of
saturating like a mean-field behavior with a single order parameter, the
measured low-temperature upper critical field increases progressively,
suggesting a large supply of superconducting states accessible via magnetic
field or low-energy thermal fluctuations. We demonstrate that superconducting
states of finite momenta can be realized within the conventional theory,
despite its questionable applicability. Our findings reveal a fundamental
characteristic of superconductivity and electronic structure in the
strongly-correlated iron-based superconductors.Comment: 10 pages, 3 figure
Epitaxial Thin Films of the Giant-Dielectric-Constant Material CaCu_3Ti_4O_{12} Grown by Pulsed-laser Deposition
Pulsed-laser deposition has been used to grow epitaxial thin films of the
giant-dielectric-constant material CaCu_3Ti_4O_{12} on LaAlO_3 and SrTiO_3
substrates with or without various conducting buffer layers. The latter include
YBa_2Cu_3O_7, La_{1.85}Sr_{0.15}CuO_{4+\delta} and LaNiO_3. Above 100K - 150K
the thin films have a temperature independent dielectric constant as do single
crystals. The value of the dielectric constant is of the order of 1500 over a
wide temperature region, potentially making it a good candidate for many
applications. The frequency dependence of its dielectric properties below 100K
- 150K indicates an activated relaxation process.Comment: 11 pages, 4 figure
Enhanced flux pinning in YBa2Cu3O7-d films by nano-scaled substrate surface roughness
Nano-scaled substrate surface roughness is shown to strongly influence the
critical current density Jc in YBCO films made by pulse-laser-deposition on the
crystalline LaAlO3 substrates consisting of two separate twin-free and
twin-rich regions. The nano-scaled corrugated surface was created in the
twin-rich region during the deposition process. Using magneto-optical imaging
techniques coupled with optical and atomic force microscopy, we observed an
enhanced flux pinning in the YBCO films in the twin-rich region, resulted in
\~30% increase in Jc, which was unambiguously confirmed by the direct transport
measurement.Comment: 16 pages, 3 figures, accepted by Applied Physics Letter
Spatial Correlations in Dynamical Mean Field Theory
We further develop an extended dynamical mean field approach introduced
earlier. It goes beyond the standard dynamical mean field theory by
incorporating quantum fluctuations associated with intersite (RKKY-like)
interactions. This is achieved by scaling the intersite interactions to the
same power in 1/D as that for the kinetic terms. In this approach, a correlated
lattice problem is reduced to a single-impurity Anderson model with additional
self-consistent bosonic baths. Here, we formulate the approach in terms of
perturbation expansions. We show that the two-particle vertex functions are
momentum-dependent, while the single-particle self-energy remains local. In
spite of this, the approach is conserving. Finally, we also determine the form
of a momentum-dependent dynamical susceptibility; the resulting expression
relates it to the corresponding Weiss field, local correlation function and
(momentum-dependent) intersite coupling.Comment: 28 pages, REVTEX, 8 figures include
A grid-based infrastructure for distributed retrieval
In large-scale distributed retrieval, challenges of latency, heterogeneity, and dynamicity emphasise the importance of infrastructural support in reducing the development costs of state-of-the-art solutions. We present a service-based infrastructure for distributed retrieval which blends middleware facilities and a design framework to ‘lift’ the resource sharing approach and the computational services of a European Grid platform into the domain of e-Science applications. In this paper, we give an overview of the DILIGENT Search Framework and illustrate its exploitation in the field of Earth Science
Mixed-valent regime of the two-channel Anderson impurity as a model for UBe_13
We investigate the mixed-valent regime of a two-configuration Anderson
impurity model for uranium ions, with separate quadrupolar and magnetic
doublets. With a new Monte Carlo approach and the non-crossing approximation we
find: (i) A non-Fermi-liquid fixed point with two-channel Kondo model critical
behavior; (ii) Distinct energy scales for screening the low-lying and excited
doublets; (iii) A semi-quantitative explanation of magnetic-susceptibility data
for UThBe assuming 60-70% quadrupolar doublet ground-state
weight, supporting the quadrupolar-Kondo interpretation.Comment: 4 Pages, 3 eps figures; submitted to Phys. Rev. Let
Asymptotically exact solution of a local copper-oxide model
We present an asymptotically exact solution of a local copper-oxide model
abstracted from the multi-band models. The phase diagram is obtained through
the renormalization-group analysis of the partition function. In the strong
coupling regime, we find an exactly solved line, which crosses the quantum
critical point of the mixed valence regime separating two different
Fermi-liquid (FL) phases. At this critical point, a many-particle resonance is
formed near the chemical potential, and a marginal-FL spectrum can be derived
for the spin and charge susceptibilities.Comment: 11 pages, 1 postcript figure is appended as self-extracting archive,
Revtex 2.0, ICTP preprint 199
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A highly flexible and compact magnetoresistive analytic device
A grand vision of realization of smart and compact multifunctional microfluidic devices for wearable health monitoring, environment sensing and point-of-care tests emerged with the fast development of flexible electronics. As a vital component towards this vision, magnetic functionality in flexible fluidics is still missing although demanded by the broad utility of magnetic nanoparticles in medicine and biology. Here, we demonstrate the first flexible microfluidic analytic device with integrated high-performance giant magnetoresistive (GMR) sensors. This device can be bent to a radius of 2 mm while still retaining its full performance. Various dimensions of magnetic emulsion droplets can be probed with high precision using a limit of detection of 0.5 pl, providing broad applicability in high-throughput droplet screening, flow cytometry and drug development. The flexible feature of this analytic device holds great promise in the realization of wearable, implantable multifunctional platforms for biomedical, pharmaceutical and chemical applications
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