3,214 research outputs found
Creating better superconductors by periodic nanopatterning
The quest to create superconductors with higher transition temperatures is as
old as superconductivity itself. One strategy, popular after the realization
that (conventional) superconductivity is mediated by phonons, is to chemically
combine different elements within the crystalline unit cell to maximize the
electron-phonon coupling. This led to the discovery of NbTi and Nb3Sn, to name
just the most technologically relevant examples. Here, we propose a radically
different approach to transform a `pristine' material into a better (meta-)
superconductor by making use of modern fabrication techniques: designing and
engineering the electronic properties of thin films via periodic patterning on
the nanoscale. We present a model calculation to explore the key effects of
different supercells that could be fabricated using nanofabrication or
deliberate lattice mismatch, and demonstrate that specific pattern will enhance
the coupling and the transition temperature. We also discuss how numerical
methods could predict the correct design parameters to improve
superconductivity in materials including Al, NbTi, and MgB
Signatures of unconventional pairing in near-vortex electronic structure of LiFeAs
A major question in Fe-based superconductors remains the structure of the
pairing, in particular whether it is of unconventional nature. The electronic
structure near vortices can serve as a platform for phase-sensitive
measurements to answer this question. By solving Bogoliubov-de Gennes equations
for LiFeAs, we calculate the energy-dependent local electronic structure near a
vortex for different nodeless gap-structure possibilities. At low energies, the
local density of states (LDOS) around a vortex is determined by the
normal-state electronic structure. However, at energies closer to the gap
value, the LDOS can distinguish an anisotropic from a conventional isotropic
s-wave gap. We show within our self-consistent calculation that in addition,
the local gap profile differs between a conventional and an unconventional
pairing. We explain this through admixing of a secondary order parameter within
Ginzburg-Landau theory. In-field scanning tunneling spectroscopy near vortices
can therefore be used as a real-space probe of the gap structure
Superconductivity and local non-centrosymmetricity in crystal lattices
Symmetry of the crystal lattice can be a determining factor for the structure
of Cooper pairs in unconventional superconductors. In this study we extend the
discussion of superconductivity in non-centrosymmetric materials to the case
when inversion symmetry is missing locally, but is present on a global level.
Concretely, we investigate the staggered non-centrosymmetricity within a
regular sublattice structure, in some analogy to the discussion of
superconductivity in antiferromagnetic systems. Three crystal structures are
analyzed in detail as illustrative examples for the extended classification of
Cooper-pairing channels. One of the cases may be relevant for the class of
iron-pnictide superconductors
Long-term storage and age‐biased export of fluvial organic carbon: field evidence from West Iceland
Terrestrial organic carbon (OC) plays an important role in the carbon cycle, but questions remain regarding the controls and timescale(s) over which atmospheric CO₂ remains sequestered as particulate OC (POC). Motivated by observations that terrestrial POC is physically stored within soils and other shallow sedimentary deposits, we examined the role that sediment storage plays in the terrestrial OC cycle. Specifically, we tested the hypothesis that sediment storage impacts the age of terrestrial POC. We focused on the Efri Haukadalsá River catchment in Iceland as it lacks ancient sedimentary bedrock that would otherwise bias radiocarbon‐based determinations of POC storage duration by supplying pre‐aged “petrogenic” POC.
Our radiocarbon measurements of riverine suspended sediments and deposits implicated millennial‐scale storage times. Comparison between the sample types (suspended and deposits) suggested an age offset between transported (suspended sediments) and stored (deposits) POC at the time of sampling, which is predicted by theory for the sediment age distribution in floodplains. We also observed that POC in suspended sediments is younger than the predicted mean storage duration generated from independent geomorphological data, which suggested an additional role for OC cycling. Consistent with this, we observed interparticle heterogeneity in the composition of POC by imaging our samples at the microscale using X‐ray absorption spectroscopy. Specifically, we found that particles within individual samples differed in their sulfur oxidation state, which is indicative of multiple origins and/or diagenetic histories. Altogether, our results support recent coupled sediment storage and OC cycling models and indicate that the physical drivers of sediment storage are important factors controlling the cadence of carbon cycling
Geometry and kinematics of the Nuncios detachment fold complex: implications for lithotectonics in northeastern Mexico
Using recent geologic mapping combined with
digital elevation data, aerial photo interpretation, and
cross section balancing, we describe the threedimensional
(3-D) geometry and kinematics of the
Nuncios Fold Complex in the Monterrey Salient of
northeastern Mexico. This map-scale, evaporite-cored
detachment fold structure involves Upper Jurassic
through Cretaceous rocks deformed during the
Laramide orogeny and comprises two westward
plunging anticlines and an intervening, eastward
plunging syncline. Seven balanced cross sections and
a 3-D model of this north vergent structure document
substantial along-strike variations in both fold
geometry and detachment depth, suggesting that 3-D
flow of the detachment layer may have occurred
during folding. Comparison of folds in the Monterrey
Salient with those in the neighboring Parras Basin
suggests that the latter south vergent folds root to a
shallower detachment. We suggest that northward
transport of the Monterrey Salient folds on the lower
evaporite detachment may have been inhibited by a
thick sequence of foreland basin rocks in the
northeastern Parras and southern La Popa basins and
that the smaller, south verging folds formed where the
lower detachment was abandoned and slip was
transferred to the shallower detachment, forming a
triangle zone at the front of the Sierra Madre orogenic
wedge
Short-range splash discharge of peridioles in Nidularia
AbstractThe distinctive shapes of basidiomata in the bird's nest fungi reflect differences in the mechanism of splash discharge. In the present study, peridiole discharge was examined in Nidularia pulvinata using high-speed video. Nidularia pulvinata produces globose basidiomata that split open at maturity to expose 100 or more peridioles within a gelatinous matrix. Each peridiole contains an estimated 7 million spores. The impact of water drops splashed the peridioles horizontally from the fruit body, along with globs of mucilage, at a mean velocity of 1.2 m s−1. Discharged peridioles travelled for a maximum horizontal distance of 1.5 cm. This launch process contrasts with the faster vertical splashes of peridioles over distances of up to one metre from the flute-shaped fruit bodies of bird's nest fungi in the genera Crucibulum and Cyathus. Peridioles in these genera are equipped with a funicular cord that attaches them to vegetation, placing them in an ideal location for ingestion by browsing herbivores. The absence of cords in N. pulvinata and its use of a sloppy discharge mechanism suggest that it is more likely to be dispersed by animals feeding on the forest floor
Observation of many-body localization of interacting fermions in a quasi-random optical lattice
We experimentally observe many-body localization of interacting fermions in a
one-dimensional quasi-random optical lattice. We identify the many-body
localization transition through the relaxation dynamics of an
initially-prepared charge density wave. For sufficiently weak disorder the time
evolution appears ergodic and thermalizing, erasing all remnants of the initial
order. In contrast, above a critical disorder strength a significant portion of
the initial ordering persists, thereby serving as an effective order parameter
for localization. The stationary density wave order and the critical disorder
value show a distinctive dependence on the interaction strength, in agreement
with numerical simulations. We connect this dependence to the ubiquitous
logarithmic growth of entanglement entropy characterizing the generic many-body
localized phase.Comment: 6 pages, 6 figures + supplementary informatio
Long-term storage and age‐biased export of fluvial organic carbon: field evidence from West Iceland
Terrestrial organic carbon (OC) plays an important role in the carbon cycle, but questions remain regarding the controls and timescale(s) over which atmospheric CO₂ remains sequestered as particulate OC (POC). Motivated by observations that terrestrial POC is physically stored within soils and other shallow sedimentary deposits, we examined the role that sediment storage plays in the terrestrial OC cycle. Specifically, we tested the hypothesis that sediment storage impacts the age of terrestrial POC. We focused on the Efri Haukadalsá River catchment in Iceland as it lacks ancient sedimentary bedrock that would otherwise bias radiocarbon‐based determinations of POC storage duration by supplying pre‐aged “petrogenic” POC.
Our radiocarbon measurements of riverine suspended sediments and deposits implicated millennial‐scale storage times. Comparison between the sample types (suspended and deposits) suggested an age offset between transported (suspended sediments) and stored (deposits) POC at the time of sampling, which is predicted by theory for the sediment age distribution in floodplains. We also observed that POC in suspended sediments is younger than the predicted mean storage duration generated from independent geomorphological data, which suggested an additional role for OC cycling. Consistent with this, we observed interparticle heterogeneity in the composition of POC by imaging our samples at the microscale using X‐ray absorption spectroscopy. Specifically, we found that particles within individual samples differed in their sulfur oxidation state, which is indicative of multiple origins and/or diagenetic histories. Altogether, our results support recent coupled sediment storage and OC cycling models and indicate that the physical drivers of sediment storage are important factors controlling the cadence of carbon cycling
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