ABSTRACT
The Ruddlesden Popper Nickelates have the general chemical formula A(N+1)Ni(N)O(3N+1) they include the cubic LaNiO3 for N=∞ and the much studied La2NiO4 similar to the cuprates and La3Ni2O7 and La4Ni3O10 etc. which all have NiO2 planes which come in singles, pairs or trimers that are internally couple. The average formal valence is 3+, 2+, 2.5+, 2..67 respectively. I will use both exact diagonalization and hybrid functional results finding that both results point squarely at the Ni being nominally 2+ and the extra hole is distributed over mainly the in plane O 2p orbitals which couple with the x2-y2 d orbitals in either a Zhang Rice singlet like fashion or in a 3 spin polaron in a fashion similar to the cuprate superconductors and in the cubic ReNiO3 systems. This leaves the inner apex O in a formal 2- state which mediates a strong super exchange interaction between the two connecting d3z2r2 orbitals . This leads us to a model of spin and charge density waves in plane and local singlet states involving the 3z2-r2 and interplanar O pz orbitals. This may also lead to a unique pairing mechanism.
BIOGRAPHY
Prof. George Sawatzky is a professor emeritus in the physics department of the University of British Columbia He received his education at the University of Manitoba in Canada with a PhD in physics in 1969. He then spent 31 years first as a post doctoral fellow and then as a professor at the University of Groningen in the Netherlands in the departments of Physics and Chemistry. He was director of the Material Science Center at the University of Groningen for 8 years. More than 40 PhD students have graduated in his research group. In 2001 he returned to Canada with a Canada research chair at the University of British Columbia were he founded the Quantum Matter Institute in 2010 and together with Dr Bernhard Keimer the Mac Planck UBC materials research center which presently also includes the University of Tokyo .
Prof. Sawatzky’s research focuses on the electronic structure of strongly correlated materials, such as magnetic materials, high temperature superconductors, and materials for molecular electronics applications; He combines theory and experiment to develop new insights and also new experimental techniques specifically x ray based spectroscopies.
Prof. Sawatzky ins member of the royal society of London, the royal society of Canada and the royal academy of sciences in the Netherlands were he was knighted in the order of the lion. He has received a number of awards including the Spinoza prize of the Netherlands. And has served in numerous advisories boards including the Max Institute of solid state physics in Stuttgart and the Korian Institute for basic science.
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