1,515 research outputs found
Extent of Fermi-surface reconstruction in the high-temperature superconductor HgBaCuO
High magnetic fields have revealed a surprisingly small Fermi-surface in
underdoped cuprates, possibly resulting from Fermi-surface reconstruction due
to an order parameter that breaks translational symmetry of the crystal
lattice. A crucial issue concerns the doping extent of this state and its
relationship to the principal pseudogap and superconducting phases. We employ
pulsed magnetic field measurements on the cuprate HgBaCuO to
identify signatures of Fermi surface reconstruction from a sign change of the
Hall effect and a peak in the temperature-dependent planar resistivity. We
trace the termination of Fermi-surface reconstruction to two hole
concentrations where the superconducting upper critical fields are found to be
enhanced. One of these points is associated with the pseudogap end-point near
optimal doping. These results connect the Fermi-surface reconstruction to both
superconductivity and the pseudogap phenomena.Comment: 5 pages. 3 Figures. PNAS (2020
Managing Risk of Bidding in Display Advertising
In this paper, we deal with the uncertainty of bidding for display
advertising. Similar to the financial market trading, real-time bidding (RTB)
based display advertising employs an auction mechanism to automate the
impression level media buying; and running a campaign is no different than an
investment of acquiring new customers in return for obtaining additional
converted sales. Thus, how to optimally bid on an ad impression to drive the
profit and return-on-investment becomes essential. However, the large
randomness of the user behaviors and the cost uncertainty caused by the auction
competition may result in a significant risk from the campaign performance
estimation. In this paper, we explicitly model the uncertainty of user
click-through rate estimation and auction competition to capture the risk. We
borrow an idea from finance and derive the value at risk for each ad display
opportunity. Our formulation results in two risk-aware bidding strategies that
penalize risky ad impressions and focus more on the ones with higher expected
return and lower risk. The empirical study on real-world data demonstrates the
effectiveness of our proposed risk-aware bidding strategies: yielding profit
gains of 15.4% in offline experiments and up to 17.5% in an online A/B test on
a commercial RTB platform over the widely applied bidding strategies
Readout of superconducting flux qubit state with a Cooper pair box
We study a readout scheme of superconducting flux qubit state with a Cooper
pair box as a transmon. The qubit states consist of the superpositions of two
degenerate states where the charge and phase degrees of freedom are entangled.
Owing to the robustness of transmon against external fluctuations, our readout
scheme enables the quantum non-demolition and single-shot measurement of flux
qubit states. The qubit state readout can be performed by using the non-linear
Josephson amplifiers after a -rotation driven by an ac-electric field.Comment: to appear in J. Phys.:Condensed Matte
Scale-invariant magnetic anisotropy in RuCl at high magnetic fields
In RuCl, inelastic neutron scattering and Raman spectroscopy reveal a
continuum of non-spin-wave excitations that persists to high temperature,
suggesting the presence of a spin liquid state on a honeycomb lattice. In the
context of the Kitaev model, magnetic fields introduce finite interactions
between the elementary excitations, and thus the effects of high magnetic
fields - comparable to the spin exchange energy scale - must be explored. Here
we report measurements of the magnetotropic coefficient - the second derivative
of the free energy with respect to magnetic field orientation - over a wide
range of magnetic fields and temperatures. We find that magnetic field and
temperature compete to determine the magnetic response in a way that is
independent of the large intrinsic exchange interaction energy. This emergent
scale-invariant magnetic anisotropy provides evidence for a high degree of
exchange frustration that favors the formation of a spin liquid state in
RuCl.Comment: arXiv admin note: substantial text overlap with arXiv:1901.09245.
Nature Physic
Allylic ionic liquid electrolyte-assisted electrochemical surface passivation of LiCoO2 for advanced, safe lithium-ion batteries
Room-temperature ionic liquid (RTIL) electrolytes have attracted much attention for use in advanced, safe lithium-ion batteries (LIB) owing to their nonvolatility, high conductivity, and great thermal stability. However, LIBs containing RTIL-electrolytes exhibit poor cyclability because electrochemical side reactions cause problematic surface failures of the cathode. Here, we demonstrate that a thin, homogeneous surface film, which is electrochemically generated on LiCoO2 from an RTIL-electrolyte containing an unsaturated substituent on the cation (1-allyl-1-methylpiperidinium bis(trifluoromethanesulfonyl)imide, AMPip-TFSI), can avert undesired side reactions. The derived surface film comprised of a high amount of organic species from the RTIL cations homogenously covered LiCoO2 with a ,25 nm layer and helped suppress unfavorable thermal reactions as well as electrochemical side reactions. The superior performance of the cell containing the AMPip-TFSI electrolyte was further elucidated by surface, electrochemical, and thermal analyses.open1
Correlation of conductivity and angle integrated valence band photoemission characteristics in single crystal iron perovskites for 300 K < T < 800 K: Comparison of surface and bulk sensitive methods
A single crystal monolith of La0.9Sr0.1FeO3 and thin pulsed laser deposited
film of La0.8Sr0.2Fe0.8Ni0.2O3 were subject to angle integrated valence band
photoemission spectroscopy in ultra high vacuum and conductivity experiments in
ambient air at temperatures from 300 K to 800 K. Except for several sputtering
and annealing cycles, the specimen were not prepared in-situ.. Peculiar changes
in the temperature dependent, bulk representative conductivity profile as a
result of reversible phase transitions, and irreversible chemical changes are
semi-quantitatively reflected by the intensity variation in the more surface
representative valence band spectra near the Fermi energy. X-ray photoelectron
diffraction images reflect the symmetry as expected from bulk iron perovskites.
The correlation of spectral details in the valence band photoemission spectra
(VB PES) and details of the conductivity during temperature variation suggest
that valuable information on electronic structure and transport properties of
complex materials may be obtained without in-situ preparation
Thermal expansion, heat capacity and magnetostriction of RAl (R = Tm, Yb, Lu) single crystals
We present thermal expansion and longitudinal magnetostriction data for cubic
RAl3 (R = Tm, Yb, Lu) single crystals. The thermal expansion coefficient for
YbAl3 is consistent with an intermediate valence of the Yb ion, whereas the
data for TmAl3 show crystal electric field contributions and have strong
magnetic field dependencies. de Haas-van Alphen-like oscillations were observed
in the magnetostriction data of YbAl3 and LuAl3, several new extreme orbits
were measured and their effective masses were estimated. Zero and 140 kOe
specific heat data taken on both LuAl3 and TmAl3 for T < 200 K allow for the
determination of a CEF splitting scheme for TmAl3
Superconducting receiver coils for sodium magnetic resonance imaging
Presents the results from sodium magnetic resonance imaging (MRI) experiments using high-temperature superconducting (HTS) receiver coils. Sodium imaging has been shown to have great potential for the assessment of cell integrity but suffers from substantially lower signal-to-noise ratio (SNR) than that of hydrogen imaging. The use of an HTS receiver coil was found to significantly increase the SNR relative to an equivalent copper receiver coil at room temperature. The SNR gains afforded by HTS coils can also be used to decrease the imaging time.published_or_final_versio
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