114 research outputs found
Some Considerations on the Historiographical Work of Georgios Pachymeris
No abstractNo abstrac
Some Considerations on the Historiographical Work of Georgios Pachymeris
No abstractNo abstrac
Pressure-induced lattice instabilities and superconductivity in YBa2Cu4O8 and optimally doped YBa2Cu3O7-{\delta}
Combined synchrotron angle-dispersive powder diffraction and micro-Raman
spectroscopy are used to investigate the pressure-induced lattice instabilities
that are accompanied by T anomalies in YBaCuO, in comparison with the optimally doped YBaCuO and the non-superconducting PrBaCuO. In the first two superconducting systems there is a clear
anomaly in the evolution of the lattice parameters and an increase of lattice
disorder with pressure, that starts at as well as
irreversibility that induces a hysteresis. On the contrary, in the Pr-compound
the lattice parameters follow very well the expected equation of state (EOS) up
to 7 GPa. In complete agreement with the structural data, the micro-Raman data
of the superconducting compounds show that the energy and width of the A phonons show anomalies at the same pressure range where the lattice
parameters deviate from the EOS and the average Cu2-O bond length
exhibits a strong contraction and correlate with the non-linear pressure
dependence of T. This is not the case for the non superconducting Pr
sample, clearly indicating a connection with the charge carriers. It appears
that the cuprates close to optimal doping are at the edge of lattice
instability.Comment: 6 pages, 7 figure
Lattice effects in the LaSrCuO compounds
Systematic Raman studies on several cuprates (YBaCuO, YBaCuO or BiSrCaCuO) have shown that at optimal doping the compounds
are at the edge of lattice instability; once this level is exceeded, by means
of doping or applying external hydrostatic pressure, the changes in the
transition temperature are accompanied by spectral modifications. There are
strong indications that the reduction in T is correlated with a
separation into nanoscale phases, which involve the oxygen atoms of the
CuO planes. In this work, modifications with doping in the Raman
spectra of the LaSrCuO compound are presented,
which show that spin or charge ordering is coupled with lattice distortions in
the whole doping region.Comment: 6 pages, 6 figure
Βιβλιοκρισία:Georgios Pachymeres Philosophia Book 3. In Aristotelis De Caelo Commentary, editio princeps. Prolegomena-Text-Indices by IOANNIS TELELIS [Corpus Philosophorum Medii Aevi / Commentaria in Aristotelem Byzantina 7], Athens 2016
Βιβλιοκρισία: Georgios Pachymeres Philosophia Book 3. In Aristotelis De Caelo Commentary, editio princeps. Prolegomena-Text-Indices by Ioannis Telelis [Corpus Philosophorum Medii Aevi / Commentaria in Aristotelem Byzantina 7], Athens 201
Βιβλιοκρισία:Lilia DIAMANTOPOULOU, Griechische visuelle Poesie. Von der Antike bis zum Gegenwart [Studien zur Geschichte Sudosteuropas 18], Frankfurt am Main u.a. 2016
Βιβλιοκρισία:Lilia Diamantopoulou, Griechische Visuelle Poesie. Von der Antike bis zur Gegenwart [Studien zur Geschichte Sudosteuropas 18], Peter Lang Edition, Frankfurt am Main u.a. 201
Βιβλιοκρισία:Lilia DIAMANTOPOULOU, Griechische visuelle Poesie. Von der Antike bis zum Gegenwart [Studien zur Geschichte Sudosteuropas 18], Frankfurt am Main u.a. 2016
Βιβλιοκρισία:Lilia Diamantopoulou, Griechische Visuelle Poesie. Von der Antike bis zur Gegenwart [Studien zur Geschichte Sudosteuropas 18], Peter Lang Edition, Frankfurt am Main u.a. 201
Isotope effect on the E2g phonon and mesoscopic phase separation near the electronic topological transition in Mg1-xAlxB2
We report the boron isotope effect on the E2g phonon mode by micro-Raman
spectroscopy on the ternary Mg1-xAlxB2 system, synthesized with pure isotopes
10B and 11B. The isotope coefficient on the phonon frequency is near 0.5 in the
full range decreasing near x = 0. The intraband electron-phonon (e-ph)
coupling, for the electrons in the sigma band, has been extracted from the E2g
line-width and frequency softening. Tuning the Fermi energy near the electronic
topological transition (ETT), where the sigma Fermi surface changes from 2D to
3D topology the E2g mode, shows the known Kohn anomaly on the 2D side of the
ETT and a splitting of the E2g phonon frequency into a hard and soft component
from x = 0 to x = 0.28. The results suggest a minor role of the intraband
phonon mediated pairing in the control of the high critical temperature in
Mg1-xAlxB2. The common physical features of diborides with the novel multigap
FeAs-based superconductors and cuprates is discussed.Comment: 19 pages, 6 figure
- …