Dopant Induced Enhancement of the Jahn-Teller Effect in Perovskite Cuprates

Abstract

Polarized x-ray absorption fine structure (XAFS) measurements at La and Sr sites on powder La_2−xSr_xCuO₄ finds two distinct local structures in the close vicinity of the impurity ion. The structures are explained in terms of two possible populations of lowest occupied states and, correspondingly, two values of elongation of the CuO₆ octahedrons. In the ground state, when the dopant-induced hole is in the x ² − y ² orbit, the elongation of the copper octahedron is about twice bigger compared to undoped La₂CuO₄. It is described as an enhanced Jahn-Teller (JT) effect. If the hole is in the hole-excited z ² orbital, then the anti-JT shortening of the octahedron takes place.