4,224 research outputs found
Sacudirse el desgano. Humberto Giannini acerca de la pereza
En esta ponencia, revisaremos la noción de pereza que propone el profesor Humberto Giannini con el propósito de evidenciar por qué, desde su filosofía tardía, la pereza sería una experiencia de la que hay que desprenderse en pos de establecer vínculos genuinos con los otros. La pereza es un estado anímico que, fuertemente ligado al aburrimiento y al ocio, da cuenta de una forma defectiva de la cotidianeidad, la cual es expresión de una disposición hostil a la acción. En este sentido, y puesto que en sus últimas obras la acción adquiere un rol predominante, es que debemos desperezarnos ante los otros
The magnetic structure and field dependence of the cycloid phas mediating the spin reorientation transition in CaâRuâOâ
We report a comprehensive experimental investigation of the magnetic structure of the cycloidal phase in Ca3Ru2O7, which mediates the spin reorientation transition, and establishes its magnetic phase diagram. In zero applied field, single-crystal neutron diffraction data confirms the scenario deduced from an earlier resonant x-ray scattering study: between 46.7~K <T<49.0~K the magnetic moments form a cycloid in the aâb plane with a propagation wavevector of (δ,0,1) with δâ0.025 and an ordered moment of about 1 ÎźB, with the eccentricity of the cycloid evolving with temperature. In an applied magnetic field applied parallel to the b-axis, the intensity of the (δ,0,1) satellite peaks decreases continuously up to about Îź0Hâ5 T, above which field the system becomes field polarised. Both the eccentricity of the cycloid and the wavevector increase with field, the latter suggesting an enhancement of the antiâsymmetric DzyaloshinskiiâMoriya interaction via magnetostriction effects. Transitions between the various low-temperature magnetic phases have been carefully mapped out using magnetometry and resistivity. The resulting phase diagram reveals that the cycloid phase exists in a temperature window that expands rapidly with increasing field, before transitioning to a polarised paramagnetic state at 5 T. High-field magnetoresistance measurements show that below Tâ70 K the resistivity increases continuously with decreasing temperature, indicating the inherent insulating nature at low temperatures of our high-quality, untwinned, single-crystals. We discuss our results with reference to previous reports of the magnetic phase diagram of Ca3Ru2O7 that utilised samples which were more metallic and/or poly-domain
Magnetic structure and field dependence of the cycloid phase mediating the spin reorientation transition in Ca3Ru2 O7
We report a comprehensive experimental investigation of the magnetic structure of the cycloidal phase in Ca3Ru2O7, which mediates the spin reorientation transition and establishes its magnetic phase diagram. In zero applied field, single-crystal neutron diffraction data confirm the scenario deduced from an earlier resonant x-ray scattering study: For 46.7K <T< 49.0 K the magnetic moments form a cycloid in the a-b plane with a propagation wave vector of (δ,0,1) with δâ0.025 and an ordered moment of about 1ÎźB, with the eccentricity of the cycloid evolving with temperature. In an applied magnetic field applied parallel to the b axis, the intensity of the (δ,0,1) satellite peaks decreases continuously up to about Îź0Hâ5T, above which field the system becomes field polarized. Both the eccentricity of the cycloid and the wave vector increase with field, the latter suggesting an enhancement of the antisymmetric Dzyaloshinskii-Moriya interaction over the symmetric exchange interactions via magnetostriction effects. Transitions between the various low-temperature magnetic phases have been carefully mapped out using magnetometry and resistivity. The resulting phase diagram reveals that the cycloid phase exists in a temperature window that expands rapidly with increasing field, before transitioning to a polarized paramagnetic state at 5 T. High-field magnetoresistance measurements show that below Tâ70K the resistivity increases continuously with decreasing temperature, indicating the inherent insulating nature at low temperatures of our high-quality, untwinned, single crystals. We discuss our results with reference to previous reports of the magnetic phase diagram of Ca3Ru2O7 that utilized samples which were more metallic and/or polydomain
Spin-orbit coupling in a half-filled shell: the case of KReCl
The half-filled shell of the configuration usually, in LS
coupling, hosts a S = 3/2 ground state with quenched orbital moment. This state
is not Jahn-Teller active. Sufficiently large spin-orbit coupling has
been predicted to change this picture by mixing in orbital moment, giving rise
to a sizable Jahn-Teller distortion. In KReCl we study the
electronic excitations using resonant inelastic x-ray scattering (RIXS) and
optical spectroscopy. We observe on-site intra- excitations below 2 eV
and corresponding overtones with two intra- excitations on adjacent
sites, the Mott gap at 2.7 eV, -to- excitations above 3 eV, and
charge-transfer excitations at still higher energy. The intra-
excitation energies are a sensitive measure of and Hund's coupling
. The sizable value of 0.29 eV places KReCl into
the intermediate coupling regime, but is not
sufficiently large to drive a pronounced Jahn-Teller effect. We discuss the
ground state wavefunction in a Kanamori picture and find that the S = 3/2
multiplet still carries about 97 % of the weight. However, the finite admixture
of orbital moment allows for subtle effects. We discuss small
temperature-induced changes of the optical data and find evidence for a
lowering of the ground state by about 3 meV below the structural phase
transitions.Comment: 16 pages, 14 figure
Wideband THz time domain spectroscopy based on optical rectification and electro-optic sampling
We present an analytical model describing the full electromagnetic propagation in a THz time-domain spectroscopy (THz-TDS) system, from the THz pulses via Optical Rectification to the detection via Electro Optic-Sampling. While several investigations deal singularly with the many elements that constitute a THz-TDS, in our work we pay particular attention to the modelling of the time-frequency behaviour of all the stages which compose the experimental set-up. Therefore, our model considers the following main aspects: (i) pump beam focusing into the generation crystal; (ii) phase-matching inside both the generation and detection crystals; (iii) chromatic dispersion and absorption inside the crystals; (iv) Fabry-Perot effect; (v) diffraction outside, i.e. along the propagation, (vi) focalization and overlapping between THz and probe beams, (vii) electro-optic sampling. In order to validate our model, we report on the comparison between the simulations and the experimental data obtained from the same set-up, showing their good agreement
Electronic excitations in J=0 Os halides studied by RIXS and optical spectroscopy
We demonstrate that the cubic antifluorite-type halides KOsCl,
KOsBr, and RbOsBr are excellent realizations of non-magnetic
J=0 compounds. The magnetic susceptibility shows the corresponding Van-Vleck
type behavior and no sign of defects. We investigate the electronic excitations
with two complementary techniques, resonant inelastic x-ray scattering (RIXS)
and optical spectroscopy. This powerful combination allows us to thoroughly
study, e.g., on-site intra- excitations and -to-
excitations as well as inter-site excitations across the Mott gap and an
exciton below the gap. In this way, we determine the electronic parameters with
high accuracy, altogether yielding a comprehensive picture. In KOsCl,
we find the spin-orbit coupling constant =0.34 eV, Hund's coupling
=0.43 eV, the onset of excitations across the Mott gap at =2.2 eV,
the cubic crystal-field splitting 10Dq=3.3 eV, and the charge-transfer energy
=4.6 eV. With =1.3, KOsCl is in the
intermediate-coupling regime. In a -only Kanamori picture, the above
values correspond to =0.41 eV and =0.28 eV, which is
very close to results reported for related iridates. In the tetragonal
phase at 5 K, the non-cubic crystal field causes a peak splitting of the J=1
state as small as 4 meV. Compared to KOsCl, the bromides KOsBr
and RbOsBr show about 12-14 % smaller values of 10Dq and ,
while the spin-orbit-entangled intra- excitations below 2 eV and hence
and are reduced by less than 4 %. Furthermore, the Mott gap in
KOsBr is reduced to about 1.8 eV.Comment: 14 pages, 14 figure
Strain control of a bandwidth-driven spin reorientation in CaâRuâOâ
The layered-ruthenate family of materials possess an intricate interplay of structural, electronic and magnetic degrees of freedom that yields a plethora of delicately balanced ground states. This is exemplified by Ca3Ru2O7, which hosts a coupled transition in which the lattice parameters jump, the Fermi surface partially gaps and the spins undergo a 90â in-plane reorientation. Here, we show how the transition is driven by a lattice strain that tunes the electronic bandwidth. We apply uniaxial stress to single crystals of Ca3Ru2O7, using neutron and resonant x-ray scattering to simultaneously probe the structural and magnetic responses. These measurements demonstrate that the transition can be driven by externally induced strain, stimulating the development of a theoretical model in which an internal strain is generated self-consistently to lower the electronic energy. We understand the strain to act by modifying tilts and rotations of the RuO6 octahedra, which directly influences the nearest-neighbour hopping. Our results offer a blueprint for uncovering the driving force behind coupled phase transitions, as well as a route to controlling them
Spontaneous cycloidal order mediating a spin-reorientation transition in a polar metal
We show how complex modulated order can spontaneously emerge when magnetic
interactions compete in a metal with polar lattice distortions. Combining
neutron and resonant x-ray scattering with symmetry analysis, we reveal that
the spin reorientation in CaRuO is mediated by a magnetic cycloid
whose eccentricity evolves smoothly but rapidly with temperature. We find the
cycloid to be highly sensitive to magnetic fields, which appear to continuously
generate higher harmonic modulations. Our results provide a unified picture of
the rich magnetic phases of this correlated, multi-band polar metal.Comment: 6 pages, 4 figures (+ 11 pages, 3 figures of supplemental material
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