385 research outputs found
Data Requirements for Oceanic Processes in the Open Ocean, Coastal Zone, and Cryosphere
The type of information system that is needed to meet the requirements of ocean, coastal, and polar region users was examined. The requisite qualities of the system are: (1) availability, (2) accessibility, (3) responsiveness, (4) utility, (5) continuity, and (6) NASA participation. The system would not displace existing capabilities, but would have to integrate and expand the capabilities of existing systems and resolve the deficiencies that currently exist in producer-to-user information delivery options
Structural and Physical Properties of CaFe4As3 Single Crystals
We report the synthesis, and structural and physical properties of CaFe4As3
single crystals. Needle-like single crystals of CaFe4As3 were grown out of Sn
flux and the compound adopts an orthorhombic structure as determined by X-ray
diffraction measurements. Electrical, magnetic, and thermal properties indicate
that the system undergoes two successive phase transitions occurring at TN1 ~
90 K and TN2 ~ 26 K. At TN1, electrical resistivities (\rho(b) and \rho(ac))
are enhanced while magnetic susceptibilities (\chi(b) and \chi(ac)) are reduced
in both directions parallel and perpendicular to the b-axis, consistent with
the scenario of antiferromagnetic spin-density-wave formation. At TN2, specific
heat reveals a slope change, and \chi(ac) decreases sharply but \chi(b) has a
clear jump before it decreases again with decreasing temperature. Remarkably,
both \rho(b) and \rho(ac) decrease sharply with thermal hysteresis, indicating
the first-order nature of the phase transition at TN2. At low temperatures,
\rho(b) and \rho(ac) can be described by {\rho} = {\rho}0 + AT^\alpha ({\rho}0,
A, and {\alpha} are constants). Interestingly, these constants vary with
applied magnetic field. The ground state of CaFe4As3 is discussed.Comment: 15 pages, 8 figures, Submitted to Physical Review
Origin of the butterfly magnetoresistance in a Dirac nodal-line system
We report a study on the magnetotransport properties and on the Fermi
surfaces (FS) of the ZrSi(Se,Te) semimetals. Density Functional Theory (DFT)
calculations, in absence of spin orbit coupling (SOC), reveal that both the Se
and the Te compounds display Dirac nodal lines (DNL) close to the Fermi level
at symmorphic and non-symmorphic positions, respectively. We
find that the geometry of their FSs agrees well with DFT predictions. ZrSiSe
displays low residual resistivities, pronounced magnetoresistivity, high
carrier mobilities, and a butterfly-like angle-dependent magnetoresistivity
(AMR), although its DNL is not protected against gap opening. As in
CdAs, its transport lifetime is found to be 10 to 10 times
larger than its quantum one. ZrSiTe, which possesses a protected DNL, displays
conventional transport properties. Our evaluation indicates that both compounds
most likely are topologically trivial. Nearly angle-independent effective
masses with strong angle dependent quantum lifetimes lead to the butterfly AMR
in ZrSiSe
Detailed study of the Fermi surfaces of the type-II Dirac semimetallic candidates XTe2 (X =Pd, Pt)
We present a detailed quantum oscillatory study on the Dirac type-II semimetallic candidates PdTe2 and PtTe2 via the temperature and the angular dependence of the de Haas-van Alphen (dHvA) and Shubnikov-de Haas (SdH) effects. In high quality single crystals of both compounds, i.e. displaying carrier mobilities between 10 3 and 10 4 cm 2 /Vs, we observed a large non-saturating magnetoresistivity (MR) which in PtTe 2 at a temperature T = 1. 3 K, leads to an increase in the resistivity up to 5 × 10 4 % under a magnetic field μ 0 H = 62 T. These high mobilities correlate with their light effective masses in the range of 0.04 to 1 bare electron mass according to our measurements. For PdTe2 the experimentally determined Fermi surface cross-sectional areas show an excellent agreement with those resulting from band-structure calculations. Surprisingly, this is not the case for PtTe2 whose agreement between calculations and experiments is relatively poor even when electronic correlations are included in the calculations. Therefore, our study provides a strong support for the existence of a Dirac type-II node in PdTe 2 and probably also for PtTe2. Band structure calculations indicate that the topologically non-trivial bands of PtTe2 do not cross the Fermi-level (εF). In contrast, for PdTe2 the Dirac type-II cone does intersect εF, although our calculations also indicate that the associated cyclotron orbit on the Fermi surface is located in a distinct kz plane with respect to the one of the Dirac type-II node. Therefore it should yield a trivial Berry-phase
Lifeworld Inc. : and what to do about it
Can we detect changes in the way that the world turns up as they turn up? This paper makes such an attempt. The first part of the paper argues that a wide-ranging change is occurring in the ontological preconditions of Euro-American cultures, based in reworking what and how an event is produced. Driven by the security – entertainment complex, the aim is to mass produce phenomenological encounter: Lifeworld Inc as I call it. Swimming in a sea of data, such an aim requires the construction of just enough authenticity over and over again. In the second part of the paper, I go on to argue that this new world requires a different kind of social science, one that is experimental in its orientation—just as Lifeworld Inc is—but with a mission to provoke awareness in untoward ways in order to produce new means of association. Only thus, or so I argue, can social science add to the world we are now beginning to live in
Bulk fermi surface of the Weyl type-II semimetallic candidate γ−MoTe2
The electronic structure of WTe and orthorhombic MoTe, are
claimed to contain pairs of Weyl type-II points. A series of ARPES experiments
claim a broad agreement with these predictions. We synthesized single-crystals
of MoTe through a Te flux method to validate these predictions through
measurements of its bulk Fermi surface (FS) \emph{via} quantum oscillatory
phenomena. We find that the superconducting transition temperature of
MoTe depends on disorder as quantified by the ratio between the
room- and low-temperature resistivities, suggesting the possibility of an
unconventional superconducting pairing symmetry. Similarly to WTe, the
magnetoresistivity of MoTe does not saturate at high magnetic
fields and can easily surpass \%. Remarkably, the analysis of the de
Haas-van Alphen (dHvA) signal superimposed onto the magnetic torque, indicates
that the geometry of its FS is markedly distinct from the calculated one. The
dHvA signal also reveals that the FS is affected by the Zeeman-effect
precluding the extraction of the Berry-phase. A direct comparison between the
previous ARPES studies and density-functional-theory (DFT) calculations reveals
a disagreement in the position of the valence bands relative to the Fermi level
. Here, we show that a shift of the DFT valence bands relative
to , in order to match the ARPES observations, and of the DFT
electron bands to explain some of the observed dHvA frequencies, leads to a
good agreement between the calculations and the angular dependence of the FS
cross-sectional areas observed experimentally. However, this relative
displacement between electron- and hole-bands eliminates their crossings and,
therefore, the Weyl type-II points predicted for MoTe.Comment: 13 pages, 7 figures, supplementary file not included (in press
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