111 research outputs found
Multiband Superconductivity in KFe2As2: Evidence for one Isotropic and several Liliputian Energy Gaps
We report a detailed low-temperature thermodynamic investigation (heat
capacity and magnetization) of the superconducting state of KFe2As2 for H || c
axis. Our measurements reveal that the properties of KFe2As2 are dominated by a
relatively large nodeless energy gap (Delta?0 = 1.9 kBTc) which excludes dx2-y2
symmetry. We prove the existence of several additional extremely small gaps
(?Delta0 < 1.0 kBTc) that have a profound impact on the low-temperature and
low-field behavior, similar to MgB2, CeCoIn5 and PrOs4Sb12. The zero-field heat
capacity is analyzed in a realistic self-consistent 4-band BCS model which
qualitatively reproduces the recent laser ARPES results of Okazaki et al.
(Science 337 (2012) 1314). Our results show that extremely low-temperature
measurements, i.e. T < 0.1 K, will be required in order to resolve the question
of the existence of line nodes in this compound.Comment: 7 pages, 6 figure
Electronic nematicity in URu2Si2 revisited
The nature of the hidden-order (HO) state in URu2Si2 remains one of the major
unsolved issues in heavy-fermion physics. Recently, torque magnetometry, x-ray
diffraction and elastoresistivity data have suggested that the HO phase
transition at THO = 17.5 K is driven by electronic nematic effects. Here, we
search for thermodynamic signatures of this purported structural instability
using anisotropic thermal-expansion, Young\'s modulus, elastoresistivity and
specific-heat measurements. In contrast to the published results, we find no
evidence of a rotational symmetry-breaking in any of our data. Interestingly,
our elastoresistivity measurements, which are in full agreement with published
results, exhibit a Curie-Weiss divergence, which we however attribute to a
volume and not to a symmetry-breaking effect. Finally, clear evidence for
thermal fluctuations is observed in our heat-capacity data, from which we
estimate the HO correlation length.Comment: 4 Figures, 5 page
Interplay of stripe and double-Q magnetism with superconductivity in under the influence of magnetic fields
At
undergoes a
novel first-order transition from a four-fold symmetric double-Q magnetic phase
to a two-fold symmetric single-Q phase, which was argued to occur
simultaneously with the onset of superconductivity (B\"ohmer et al., Nat. Comm.
6, 7911 (2015)). Here, by applying magnetic fields up to 10T, we investigate in
more detail the interplay of superconductivity with this magneto-structural
transition using a combination of high-resolution thermal-expansion and
heat-capacity measurements. We find that a magnetic field suppresses the
reentrance of the single-Q orthorhombic phase more strongly than the
superconducting transition, resulting in a splitting of the zero-field
first-order transition. The suppression rate of the orthorhombic reentrance
transition is stronger for out-of-plane than for in-plane fields and scales
with the anisotropy of the superconducting state. These effects are captured
within a phenomenological Ginzburg-Landau model, strongly suggesting that the
suppression of the reentrant orthorhombic single-Q phase is primarily linked to
the field-induced weakening of the superconducting order. Not captured by this
model is however a strong reduction of the orthorhombic distortion for
out-of-plane fields, which deserves further theoretical attention
Outside-in disk evolution in the LMC
From the analysis of the color-magnitude diagrams and color functions of four
wide LMC fields located from ~2 to 6 kpc from the kinematic center of the LMC
we present evidence that, while the oldest population is coeval in all fields,
the age of the youngest component of the dominant stellar population gradually
increases with galactocentric distance, from currently active star formation in
a field at 2.3 deg, to 100 Myr, 0.8 Gyr, and 1.5 Gyr in fields at 4.0 deg, 5.5
deg, and 7.1 deg, respectively. This outside-in quenching of the star formation
in the LMC disk is correlated with the decreasing HI column density (which is <
2x 10^{20} cm^{-2} in the two outermost fields with little or no current star
formation. Other work in the literature hints at similar behavior in the
stellar populations of irregular galaxies, and in M33. This is observational
evidence against the inside-out disk formation scenario in low-mass spirals and
irregular galaxies. Alternatively, it could be that the age distribution with
radius results from interplay between the evolution with time of the
star-forming area of the LMC and the subsequent outward migration of the stars.Comment: 6 pages, 2 figures, ApJ Letters, in pres
Colossal c-axis response and lack of rotational symmetry breaking within the kagome plane of the CsVSb superconductor
The kagome materials AV4Sb (A = K, Rb, Cs) host an intriguing
interplay between unconventional superconductivity and charge-density-waves.
Here, we investigate CsVSb by combining high-resolution
thermal-expansion, heat-capacity and electrical resistance under strain
measurements. We directly unveil that the superconducting and charge-ordered
states strongly compete, and that this competition is dramatically influenced
by tuning the crystallographic c-axis. In addition, we report the absence of
additional bulk phase transitions within the charge-ordered state, notably
associated with rotational symmetry-breaking within the kagome planes. This
suggests that any breaking of the C invariance occurs via different
stacking of C-symmetric kagome patterns. Finally, we find that the
charge-density-wave phase exhibits an enhanced A-symmetric
elastoresistance coefficient, whose large increase at low temperature is driven
by electronic degrees of freedom
Digital tools for brownfield redevelopment: Stakeholder perspectives and opportunities
Brownfield redevelopment is a complex process often involving a wide range of stakeholders holding differing priorities and opinions. The use of digital systems and products for decision making, modelling, and supporting discussion has been recognised throughout literature and industry. The inclusion of stakeholder preferences is an important consideration in the design and development of impactful digital tools and decision support systems. In this study, we present findings from stakeholder consultation with professionals from the UK brownfield sector with the aim of informing the design of future digital tools and systems. Our research investigates two broad themes; digitalisation and the use of digital tools across the sector; and perceptions of key brownfield challenge areas where digital tools could help better inform decision-makers. The methodology employed for this study comprises the collection of data and information using a combination of interviews and an online questionnaire. The results from these methods were evaluated both qualitatively and quantitatively. Findings reveal a disparity in levels of digital capability between stakeholder groups including between technical stakeholder types, and that cross-discipline communication of important issues may be aided by the development of carefully designed digital tools. To this end, we present seven core principles to guide the design and implementation of future digital tools for the brownfield sector. These principles are that future digital tools should be: (1) Stakeholder driven, (2) Problem centred, (3) Visual, (4) Intuitive, (5) Interactive, (6) Interoperable, and (7) Geospatial data driven
A critical review of decision support systems for brownfield redevelopment
Over the past two decades, many decision support systems (DSSs) have been developed to support decision makers and facilitate the planning and redevelopment process of brownfields. Existing systems are however often siloed in their approach and do not fully capture the complexity of brownfield sites from a sustainable development point of view. This critical review provides an insight into the development and implementation of DSSs, published and emerging, together with assessment of their strengths, limitations and opportunities for future integration. Brownfields DSS applications include: remediation technology selection; and land use planning; and risk assessment. The results of this review lead the authors to identify four opportunities to improve brownfield DSSs: (i) increased use of qualitative socioeconomic criteria, particularly costs and economic variables, (ii) decision-support during the early stages of brownfield redevelopment, (iii) the integration of predictive modelling methods, and (iv) improvements of user interfaces and modern web-based functionalities
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