9 research outputs found
Softening of a flat phonon mode in the kagome ScVSn
The long range electronic modulations recently discovered in the
geometrically frustrated kagome lattice have opened new avenues to explore the
effect of correlations in materials with topological electron flat bands. The
observation of the lattice response to the emergent new phases of matter, a
soft phonon mode, has remained elusive and the microscopic origin of charge
density waves (CDWs) is still unknown. Here, we show, for the first time, a
complete melting of the ScVSn (166) kagome lattice. The low energy
phonon with propagation vector collapses
at 98 K, without the emergence of long-range charge order, which sets in with a
propagation vector . The CDW is driven
(but locks at a different vector) by the softening of an overdamped phonon flat
plane at k=. We observe broad phonon anomalies in momentum space,
pointing to (1) the existence of approximately flat phonon bands which gain
some dispersion due to electron renormalization, and (2) the effects of the
momentum dependent electron-phonon interaction in the CDW formation. Ab initio
and analytical calculations corroborate the experimental findings to indicate
that the weak leading order phonon instability is located at the wave vector
of a rather flat collapsed mode. We
analytically compute the phonon frequency renormalization from high
temperatures to the soft mode, and relate it to a peak in the orbital-resolved
susceptibility, obtaining an excellent match with both ab initio and
experimental results, and explaining the origin of the approximately flat
phonon dispersion. Our data report the first example of the collapse of a
softening of a flat phonon plane and promote the 166 compounds of the kagome
family as primary candidates to explore correlated flat phonon-topological flat
electron physics.Comment: 10 pages, 4 figure
Electronic structure and lattice dynamics of 1T-VSe: origin of the 3D-CDW
In order to characterize in detail the charge density wave (CDW) transition
of 1-VSe, its electronic structure and lattice dynamics are
comprehensively studied by means of x-ray diffraction, angle resolved
photoemission (ARPES), diffuse and inelastic x-ray scattering (IXS), and
state-of-the-art first principles density functional theory calculations.
Resonant elastic x-ray scattering (REXS) does not show any resonant enhancement
at either V or Se K-edges, indicating that the CDW peak describes a purely
structural modulation of the electronic ordering. ARPES identifies (i) a
pseudogap at TT, which leads to a depletion of the density of states
in the plane at TT, and (ii) anomalies in the electronic
dispersion reflecting a sizable impact of phonons on it. A diffuse scattering
precursor, characteristic of soft phonons, is observed at room temperature (RT)
and leads to the full collapse of the low-energy phonon () with
propagation vector (0.25 0 -0.3) r.l.u. We show that the frequency and
linewidth of this mode are anisotropic in momentum space, reflecting the
momentum dependence of the electron-phonon interaction (EPI), hence
demonstrating that the origin of the CDW is, to a much larger extent, due to
the momentum dependence EPI with a small contribution from nesting. The
pressure dependence of the soft mode remains nearly constant up to
13 GPa at RT, with only a modest softening before the transition to the
high-pressure monoclinic phase. The wide set of experimental data are
well captured by our state-of-the art first-principles anharmonic calculations
with the inclusion of van der Waals (vdW) corrections in the
exchange-correlation functional. The description of the electronics and
dynamics of VSe reported here adds important pieces of information to the
understanding of the electronic modulations of TMDs
Electronic structure and lattice dynamics of 1 T − VSe 2 : Origin of the three-dimensional charge density wave
Ionic exchange desorption of mercury from contaminated dredging sludge (at 393K and ambient temperature)
Ionic exchange desorption of mercury from contaminated dredging sludge (at 393K and ambient temperature)
Electronic structure and lattice dynamics of 1 T − VSe 2 : Origin of the three-dimensional charge density wave
Integrated Popular Reporting as a Tool for Citizen Involvement in Financial Sustainability Decisions
The more information that is disseminated about the financial impact of government decisions, the more public sector entities are stimulated to make decisions in a transparent manner. Several tools can be used to involve citizens in financial sustainability decisions; among these, popular reporting is receiving growing attention in the public sector. The goal of popular reporting is to engage the interest of average citizens and make it easy for them to understand financial sustainability, by presenting more information than traditional financial reporting, in a concise, comprehensive, and attractive manner. For these reasons, government entities should consider implementing integrated popular reporting. This chapter aims to present a prototype integrated popular report designed to promote citizen participation in financial sustainability decisions. Through a theoretical-deductive methodology, it aims to identify the main features that an integrated popular report should contain to best respond to the information needs of public sector user groups, focusing on citizens in particular
A Coupled Reactive-Transport Model for Electrokinetic Remediation
In this chapter, we present a model for the reactive-transport of chemical species through partially saturated porous media for electrokinetic remediation processes. A generalized theoretical model is presented, easily adaptable to specific remediation setups, target contaminants and supporting matrices; and we give detailed guidelines for the implementation of tailor-made numerical methods for the computer-aided solution. The model is subdivided into two coupled modules: one for reactive-transport, numerically solved by means of a non-linear finite element method; and another one for chemical equilibrium, solved using an enhanced Newton–Raphson method