arXiv subjects

Alessandro Mirone

Publications and source records attributed to Alessandro Mirone.

26 records · Page 2Linked to original sources

arXiv2012

Ground state and excitation spectra of a strongly correlated lattice by the coupled cluster method

We apply Coupled Cluster Method to a strongly correlated lattice and develop the Spectral Coupled Cluster equations by finding an approximation to the resolvent operator, that gives the spectral response for an certain class of probe operators. We apply the method to a $MnO_2$ plane model with a parameters choice which corresponds to previous experimental works and which gives a non-nominal symmetry ground state. We show that this state can be observed using our Spectral Coupled Cluster Method by probing the Coupled Cluster solution obtained from the nominal reference state. In this case one observes a negative energy resonance which corresponds to the true ground state.

cond-mat.str-el↗

arXiv2009

Effect of core-valence intra-atomic quadrupolar interaction in resonant x-ray scattering at the Dy M$_{4,5}$ edges in DyB$_2$C$_2$

The dependence with energy of the resonant soft x-ray Bragg diffraction intensity in DyB$_2$C$_2$ for the $(00{1/2})$ reflection at the Dy M$_{4,5}$ edges have been calculated by using an atomic multiplet hamiltonian including the effect of crystal field and introducing an intra-atomic quadrupolar interaction between the 3d core and 4f valence shell. These calculations are compared with the experimental results (Mulders et al., J. Phys.: Condens. Matter 18 (2006) 11195) in the antiferroquadrupolar and antiferromagnetic phases of DyB$_2$C$_2$. We reproduce all the features appearing $(00{1/2})$ reflection energy profile in the antiferroquadrupolar ordered phase, and we reproduce the behaviour of the resonant x-ray scattering intensity at different energies in the vicinity of the Dy M$_5$ edge when the temperature is lowered within the antiferromagnetic phase.

cond-mat.str-el↗

arXiv2009

Hilbert++ Manual

We present here an installation guide, a hand-on mini-tutorial through examples, and the theoretical foundations of the Hilbert++ code.

cs.OH↗

arXiv2006

Computer Algebra calculation of XRMS polarisation dependence in the non spherical case

Simple analytical formulae, directly relating the experimental geometry and sample orientation to the measured R(M)XS scattered intensity are very useful to design experiments and analyse data. Such formulae can be obtained by the contraction of an expression containing the polarisations and crystal field tensors, and where the magnetisation vector acts as a rotation derivative\cite{mirone}. The result of a contraction contains a scalar product of (rotated) polarisation vectors and the crystal field axis. The contraction rules give rise to combinatorial algorithms which can be efficiently treated by computers. In this work we provide and discuss a concise Mathematica code along with a few example applications to non-centrosymmetric magnetic systems.

cond-mat.other↗

arXiv2006

X-ray Resonant Magnetic Scattering : Polarisation Dependence in the non-spherical case

We develop a simple tensorial contraction method to obtain analytical formula for X-ray resonant magnetic scattering. We apply the method considering first electric dipole-dipole and electric quadrupole-quadrupole scattering in the isolated atom approximation and compare the results with previous works. Then we apply the method to derive phenomenological original formulas which account also for non-spherical systems and for dipole-quadrupole mixing.

cond-mat.other↗

arXiv2006

Spectroscopy of orbital ordering in La0.5Sr1.5MnO4 : A many-body cluster calculation

We have studied the orbital ordering (OO) in La0.5Sr1.5MnO4 and its soft x-ray resonant diffraction spectroscopic signature at the Mn L2, L3 edges. We have modelled the system in second quantization as a small planar cluster consisting of a central Mn atom, with the first neighbouring shells of oxygen and Mn atoms. For the effective Hamiltonian we consider Slater-Koster parameters, charge transfer and electron correlation energies obtained from previous measurements on manganites. We calculate the OO as a function of oxygen distortion and spin correlation used as adjustable parameters. Their contribution as a function of temperature is clearly distinguished with a good spectroscopic agreement.

cond-mat.str-el↗

arXiv2004

Explaining the magnetic moment reduction of Fullerene encapsulated Gadolinium through a theoretical model

We propose a Theoretical model accounting for the recently observed reduced magnetic moment of Gadolinium in fullerenes. While this reduction has been observed also for other trivalent rare-hearth atoms (Dy3+, Er3+, Ho3+) in fullerenes and can be ascribed to crystal field effects, the explanation of this phenomena for Gd3+ is not straightforward due to the sphericity of its ground state (S=7/2, L=0). In our model the momentum lowering is the result of a subtle interplay between hybridisation and spin-orbit interaction.

cond-mat.str-el↗

arXiv2003

Phonon dispersion in 1-layer cuprate HgBa2CuO4+d

We investigate the low energy acoustical and optical modes in $\mathrm{HgBa_2CuO_{4+δ}}$ using inelastic x-ray scattering (IXS). The experimental phonon dispersion and the dynamical structure factor are compared with an atomic shell model, and the set of the atomic potentials obtained are discussed. Our results are also compared with those obtained by Raman spectroscopy and with density-of-state data measured by inelastic neutron scattering.

cond-mat.supr-con↗