title: A Genuine Jahn-Teller System with Compressed Geometry and Quantum Effects Originating from Zero-Point Motion.
abstract: First-principle calculations together with analysis of the experimental data found for 3d(9) and 3d(7) ions in cubic oxides proved that the center found in irradiated CaO:Ni(2+) corresponds to Ni(+) under a static Jahn-Teller effect displaying a compressed equilibrium geometry. It was also shown that the anomalous positive g∥ shift (g∥ -g0 =0.065) measured at T=20 K obeys the superposition of the |3 z(2) -r(2) ⟩ and |x(2) -y(2) ⟩ states driven by quantum effects associated with the zero-point motion, a mechanism first put forward by O'Brien for static Jahn-Teller systems and later extended by Ham to the dynamic Jahn-Teller case. To our knowledge, this is the first genuine Jahn-Teller system (i.e. in which exact degeneracy exists at the high-symmetry configuration) exhibiting a compressed equilibrium geometry for which large quantum effects allow experimental observation of the effect predicted by O'Brien. Analysis of the calculated energy barriers for different Jahn-Teller systems allowed us to explain the origin of the compressed geometry observed for CaO:Ni(+) .
authors.affiliation: Departamento de Ciencias de la Tierra y Física de la Materia Condensada, Universidad de Cantabria, Avenida de los Castros s/n, 39005, Santander, Spain. aramburj@unican.es.
authors.forename: José Antonio
authors.initials: JA
authors.lastname: Aramburu
authors.affiliation: Departamento de Ciencias de la Tierra y Física de la Materia Condensada, Universidad de Cantabria, Avenida de los Castros s/n, 39005, Santander, Spain.
authors.forename: Pablo
authors.initials: P
authors.lastname: García-Fernández
authors.affiliation: Center for Atomic-Scale Materials Design, Department of Physics, Technical University of Denmark, DK-2800, Kongens Lyngby, Denmark.
authors.forename: Juan María
authors.initials: JM
authors.lastname: García-Lastra
authors.affiliation: Departamento de Ciencias de la Tierra y Física de la Materia Condensada, Universidad de Cantabria, Avenida de los Castros s/n, 39005, Santander, Spain.
authors.forename: Miguel
authors.initials: M
authors.lastname: Moreno
keywords: Jahn-Teller distortion; O'Brien effect; ab initio calculations; compressed geometry; doping