Abstract:The authors discuss positron behaviour and in particular the ground state positron probability in high-Tc materials. Special attention is paid to La2CuO4, for which they report detailed high-resolution two-dimensional angular correlation of positron annihilation radiation spectroscopy measurements in three sample orientations and as a function of temperature. Besides a large isotropic core-like electron contribution ( approximately=85%), the remaining anisotropic contribution is attributed to valence electrons… Show more
“…For an atomic orbital, the momentum density has the same point symmetry as the corresponding charge density. This result carries over to molecular states 52 and is equally applicable to solid-state wave functions.…”
We have observed the bulk Fermi surface (FS) in an overdoped (x=0.3) single crystal of La2−xSrxCuO4 by using Compton scattering. A two-dimensional (2D) momentum density reconstruction from measured Compton profiles yields a clear FS signature in the third Brillouin zone along [100]. The quantitative agreement between density functional theory (DFT) calculations and momentum density experiment suggests that Fermi-liquid physics is restored in the overdoped regime. In particular the predicted FS topology is found to be in good accord with the corresponding experimental data. We find similar quantitative agreement between the measured 2D angular correlation of positron annihilation radiation (2D-ACAR) spectra and the DFT based computations. However, 2D-ACAR does not give such a clear signature of the FS in the extended momentum space in either the theory or the experiment.
“…For an atomic orbital, the momentum density has the same point symmetry as the corresponding charge density. This result carries over to molecular states 52 and is equally applicable to solid-state wave functions.…”
We have observed the bulk Fermi surface (FS) in an overdoped (x=0.3) single crystal of La2−xSrxCuO4 by using Compton scattering. A two-dimensional (2D) momentum density reconstruction from measured Compton profiles yields a clear FS signature in the third Brillouin zone along [100]. The quantitative agreement between density functional theory (DFT) calculations and momentum density experiment suggests that Fermi-liquid physics is restored in the overdoped regime. In particular the predicted FS topology is found to be in good accord with the corresponding experimental data. We find similar quantitative agreement between the measured 2D angular correlation of positron annihilation radiation (2D-ACAR) spectra and the DFT based computations. However, 2D-ACAR does not give such a clear signature of the FS in the extended momentum space in either the theory or the experiment.
“…Instructive examples of the importance of orbital contributions in momentum density are found from the 2D-ACAR (2-Dimensional Angular Correlation of the Annihilation Radiation) technique applied to copper oxides [3]. The momentum density anisotropies of La 2−x Sr x CuO 4 [4,5] and Tl 2−x Ba x CuO 6 [6] can be described reasonably well by a simple LCAO-MO method [2], which neglects the FS. Therefore, in these cases the chemical bonding overshadows the smaller FS effects and it is very difficult to extract the FS signal.…”
We discuss the work aimed at studying the momentum density of high T c superconducting oxides using Compton profile and positron annihilation spectroscopies.
“…The positron density concentrating near Cu-O bonds 36 and the shortest distance (1.95 Å) between Cu and O ions in a monoclinic cell of CuO were identified 37 . Therefore the effects of positron trapping at positively charged vacancies O in the whole range of the Fermi level in both n-type and p-type CuO in the O-rich environment, respectively.…”
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