493 research outputs found
Interplay between Kondo suppression and Lifshitz transitions in YbRhSi at high magnetic fields
We investigate the magnetic field dependent thermopower, thermal
conductivity, resistivity and Hall effect in the heavy fermion metal YbRh2Si2.
In contrast to reports on thermodynamic measurements, we find in total three
transitions at high fields, rather than a single one at 10 T. Using the Mott
formula together with renormalized band calculations, we identify Lifshitz
transitions as their origin. The predictions of the calculations show that all
experimental results rely on an interplay of a smooth suppression of the Kondo
effect and the spin splitting of the flat hybridized bands.Comment: 5 pages, 4 figure
Understanding the needs of Mena public transport customers: culture of service and gender responsive recommendations
Fast population growth, urban sprawl and the raise in households’ motorization observed in all major cities of the Middle-East and North-Africa (MENA) region, are constantly challenging public transport providers who seek to handle efficiently the continuously rising travel demand. Most of the MENA cities suffer from traffic congestion that not only impacts the quality of life of MENA citizens, but also their access to job opportunities, health services, and social and political participation. Alongside the development of public transport network, it is crucial to encourage urban dwellers to reduce their dependence on personal cars, use public transport, and develop soft mobility skills. Therefore,
operators and service providers need to define customer-centric strategy and build a culture of service excellence in line with their customers’expectations. In cooperation with academic partners, the UITP MENA Centre for Transport Excellence launched the User-Oriented Public Transport research project with the aim to understand the perceptions of female and male users and non-users about public transport services in five MENA cities: Algiers, Amman, Beirut, Casablanca and Muscat. The methodological framework was built around the five dimensions of the user’s needs pyramid: safety, security, ease-to-use, comfort and experience. Based on the quantitative analysis of data
collected from 984 respondents and the qualitative analysis of 49 women’s testimonies collected during the focus groups, recommendations were made to encourage culture of service and gender mainstreaming in public transport development in the region
Enhancement of the Nernst effect by stripe order in a high-Tc superconductor
The Nernst effect in metals is highly sensitive to two kinds of phase
transition: superconductivity and density-wave order. The large positive Nernst
signal observed in hole-doped high-Tc superconductors above their transition
temperature Tc has so far been attributed to fluctuating superconductivity.
Here we show that in some of these materials the large Nernst signal is in fact
caused by stripe order, a form of spin / charge modulation which causes a
reconstruction of the Fermi surface. In LSCO doped with Nd or Eu, the onset of
stripe order causes the Nernst signal to go from small and negative to large
and positive, as revealed either by lowering the hole concentration across the
quantum critical point in Nd-LSCO, or lowering the temperature across the
ordering temperature in Eu-LSCO. In the latter case, two separate peaks are
resolved, respectively associated with the onset of stripe order at high
temperature and superconductivity near Tc. This sensitivity to Fermi-surface
reconstruction makes the Nernst effect a promising probe of broken symmetry in
high-Tc superconductors
Intrusion-extrusion experiments of MgCl2 aqueous solution in pure silica ferrierite: Evidence of the nature of intruded liquid by in situ high pressure synchrotron X-ray powder diffraction
Experimental intrusion-extrusion isotherms of MgCl221H2O solution were recorded at room temperature
on pure silica FER-type zeolite (Si-FER). The intrusion occurs at 195 MPa and the phenomenon is
completely reversible with a slight hysteresis. The \u201cSi-FER - MgCl2 aqueous solution\u201d system behaves like
a spring. The material was deeply characterized before and after intrusion-extrusion experiments and no
significant changes were observed. The unit cell parameters were refined e on the basis of the in situ
synchrotron X-ray powder diffraction data - up to 1.47 GPa and then at Pamb upon pressure release. The
Rietveld refinement of the data collected at 0.28 GPa (280 MPa), a pressure close to the intrusion value,
shows that both ions and water molecules present in the MgCl2 aqueous solution were intruded in the
porosities. However, the solvation degree of the intruded ions differs from the initial solution, revealing a
partial desolvation of both magnesium and chloride ions. As a whole, the nature and amount of the
intruded species correspond to a MgCl210H2O composition. Moreover, at a higher pressure (0.68 GPa), a
phase transition from the orthorhombic Pmnn to the monoclinic P21/n s.g. is observed in Si-FER. At
1.47 GPa, the zeolite maintains this monoclinic symmetry, while another phase transition, to the
monoclinic P21 s g., is argued from the analysis of the pattern of the sample compressed to 2.6 GPa and
then collected upon pressure release to ambient conditions
Origin of Drastic Change of Fermi Surface and Transport Anomalies in CeRhIn5 under Pressure
The mechanism of drastic change of Fermi surfaces as well as transport
anomalies near P=Pc=2.35 GPa in CeRhIn5 is explained theoretically. The key
mechanism is pointed out to be the interplay of magnetic order and Ce-valence
fluctuations. We show that the antiferromagnetic state with "small" Fermi
surfaces changes to the paramagnetic state with "large" Fermi surfaces with
huge enhancement of effective mass of electrons with keeping finite c-f
hybridization. This explains the drastic change of the de Haas-van Alphen
signals. Furthermore, it is also consistent with the emergence of T-linear
resistivity simultaneous with the residual resistivity peak at P=Pc in CeRhIn5.Comment: 5 pages, 3 figures, submitted to Journal of Physical Society of Japa
Broken rotational symmetry in the pseudogap phase of a high-Tc superconductor
The nature of the pseudogap phase is a central problem in the quest to
understand high-Tc cuprate superconductors. A fundamental question is what
symmetries are broken when that phase sets in below a temperature T*. There is
evidence from both polarized neutron diffraction and polar Kerr effect
measurements that time- reversal symmetry is broken, but at temperatures that
differ significantly. Broken rotational symmetry was detected by both
resistivity and inelastic neutron scattering at low doping and by scanning
tunnelling spectroscopy at low temperature, but with no clear connection to T*.
Here we report the observation of a large in-plane anisotropy of the Nernst
effect in YBa2Cu3Oy that sets in precisely at T*, throughout the doping phase
diagram. We show that the CuO chains of the orthorhombic lattice are not
responsible for this anisotropy, which is therefore an intrinsic property of
the CuO2 planes. We conclude that the pseudogap phase is an electronic state
which strongly breaks four-fold rotational symmetry. This narrows the range of
possible states considerably, pointing to stripe or nematic orders.Comment: Published version. Journal reference and DOI adde
The NICMOS Snapshot Survey of nearby Galaxies
We present ``snapshot'' observations with the NearInfrared Camera and
MultiObject Spectrometer (NICMOS) on board the Hubble Space Telescope (HST) of
94 nearby galaxies from the Revised Shapley Ames Catalog. Images with 0.2 as
resolution were obtained in two filters, a broad-band continuum filter (F160W,
roughly equivalent to the H-band) and a narrow band filter centered on the
Paschen alpha line (F187N or F190N, depending on the galaxy redshift) with the
51x51 as field of view of the NICMOS camera 3. A first-order continuum
subtraction is performed, and the resulting line maps and integrated Paschen
alpha line fluxes are presented. A statistical analysis indicates that the
average Paschen alpha surface brightness {\bf in the central regions} is
highest in early-type (Sa-Sb) spirals.Comment: Original contained error in flux calibration. Table 1 now has correct
Paschen Alpha fluxes. 14 pages LaTeX with JPEG and PS figures. Also available
at http://icarus.stsci.edu/~boeker/publications.htm
Symmetry breaking orbital anisotropy on detwinned Ba(Fe1-xCox)2As2 above the spin density wave transition
Nematicity, defined as broken rotational symmetry, has recently been observed
in competing phases proximate to the superconducting phase in the cuprate high
temperature superconductors. Similarly, the new iron-based high temperature
superconductors exhibit a tetragonal to orthorhombic structural transition
(i.e. a broken C4 symmetry) that either precedes or is coincident with a
collinear spin density wave (SDW) transition in undoped parent compounds, and
superconductivity arises when both transitions are suppressed via doping.
Evidence for strong in-plane anisotropy in the SDW state in this family of
compounds has been reported by neutron scattering, scanning tunneling
microscopy, and transport measurements. Here we present an angle resolved
photoemission spectroscopy study of detwinned single crystals of a
representative family of electron-doped iron-arsenide superconductors,
Ba(Fe1-xCox)2As2 in the underdoped region. The crystals were detwinned via
application of in-plane uniaxial stress, enabling measurements of single domain
electronic structure in the orthorhombic state. At low temperatures, our
results clearly demonstrate an in-plane electronic anisotropy characterized by
a large energy splitting of two orthogonal bands with dominant dxz and dyz
character, which is consistent with anisotropy observed by other probes. For
compositions x>0, for which the structural transition (TS) precedes the
magnetic transition (TSDW), an anisotropic splitting is observed to develop
above TSDW, indicating that it is specifically associated with TS. For
unstressed crystals, the band splitting is observed close to TS, whereas for
stressed crystals the splitting is observed to considerably higher
temperatures, revealing the presence of a surprisingly large in-plane nematic
susceptibility in the electronic structure.Comment: final version published in PNAS, including supplementary informatio
Synthesis of EMT/FAU-type zeolite nanocrystal aggregates in high yield and crystalline form
AbstractThis work focuses on different ways to improve the yield and/or the crystalline quality of EMT/FAU-type zeolite nanocrystal aggregates obtained in the presence of organic additive triethanolamine (TEA). The increase of the amount of aluminum reagent enhances the synthesis yield by a factor of 2.5 without affecting the crystallization rate and the microporous volume. On the other hand, the increase of the thermal treatment time allows to increase the synthesis yield, the crystallization rate and the microporous volume. Furthermore, addition of EMT zeolite seeds into the starting reaction medium improves the crystallization rate and the microporous volume
Linear-T resistivity and change in Fermi surface at the pseudogap critical point of a high-Tc superconductor
A fundamental question of high-temperature superconductors is the nature of
the pseudogap phase which lies between the Mott insulator at zero doping and
the Fermi liquid at high doping p. Here we report on the behaviour of charge
carriers near the zero-temperature onset of that phase, namely at the critical
doping p* where the pseudogap temperature T* goes to zero, accessed by
investigating a material in which superconductivity can be fully suppressed by
a steady magnetic field. Just below p*, the normal-state resistivity and Hall
coefficient of La1.6-xNd0.4SrxCuO4 are found to rise simultaneously as the
temperature drops below T*, revealing a change in the Fermi surface with a
large associated drop in conductivity. At p*, the resistivity shows a linear
temperature dependence as T goes to zero, a typical signature of a quantum
critical point. These findings impose new constraints on the mechanisms
responsible for inelastic scattering and Fermi surface transformation in
theories of the pseudogap phase.Comment: 24 pages, 6 figures. Published in Nature Physics. Online at
http://www.nature.com/nphys/journal/vaop/ncurrent/full/nphys1109.htm
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