Subband filling and Mott transition in Ca_{2-x}Sr_xRuO_4

TL;DR

This paper introduces a new mechanism for the metal-insulator transition in Ca_{2-x}Sr_xRuO_4, highlighting the role of structural changes and interorbital charge transfer in driving a Mott transition.

Contribution

It demonstrates how crystal field splitting and Coulomb interactions cause a Mott transition through interorbital charge transfer in this layered perovskite.

Findings

Complete filling of the d_xy band occurs due to structural effects.

A Mott transition is triggered in the half-filled d_xz,yz bands.

Structural doping influences local correlations significantly.

Abstract

A new concept is proposed for the paramagnetic metal insulator transition in the layer perovskite Ca_{2-x}Sr_xRuO_4. Whereas the pure Sr compound is metallic up to very large Coulomb energies due to strong orbital fluctuations, structural changes induced by doping with Ca give rise to a interorbital charge transfer which makes the material extremely sensitive to local correlations. Using dynamical mean field theory based on finite temperature multi-band exact diagonalization it is shown that the combination of crystal field splitting and onsite Coulomb interactions leads to complete filling of the d_xy band and to a Mott transition in the half-filled d_xz,yz bands.