Abstract
The metal-insulator transition (MIT) remains among the most thoroughly studied phenomena in solid state physics, but the complexity of the phenomena, which usually involves cooperation of many degrees of freedom including orbitals, fluctuating local moments, magnetism, and the crystal structure, have resisted predictive ab-initio treatment. Here we develop ab-initio theoretical method for correlated electron materials, based on Dynamical Mean Field Theory, which can predict the change of the crystal structure across the MIT at finite temperature. This allows us to study the coupling between electronic, magnetic and orbital degrees of freedom with the crystal structure across the MIT in rare-earth nickelates. We predict the electronic free energy profile of the competing states, and the theoretical magnetic ground state configuration, which is in agreement with neutron scattering data, but is different from the magnetic models proposed before. The resonant elastic X-ray response at the K-edge, which was argued to be a probe of the charge order, is theoretically modelled within the Dynamical Mean Field Theory, including the core-hole interaction. We show that the line-shape of the measured resonant elastic X-ray response can be explained with the “site-selective” Mott scenario without real charge order on Ni sites.
Highlights
Metal-insulator transition (MIT) in transition metal oxides is usually associated with a large Hubbard Coulomb interaction U on transition metal ion, which strongly impedes electron motion, as it costs an energy U to add an extra electron to any given site
The structurally distorted monoclinic ground state is very susceptible to small changes of external parameters and can be tuned by pressure[1], strain[4,5,6,7], reduced dimensionality[8, 9] or by layering it in heterostructures[10,11,12], it has attracted a lot of attention recently
The leading interpretation for the origin of the metal-insulator transition (MIT) is a charge disproportionation (CD) on the Ni sites, in which Ni3+ ions disproportionate into sites with excessive and deficient charge (3d73d7 → 3d7+δ3d7−δ). Such charge order would result in different energy positions of core levels on the two inequivalent Ni ions due to electrostatic effect, which can be probed by the hard resonant elastic X-ray scattering (RXS) through measuring the 1s to 4p transitions
Summary
Metal-insulator transition (MIT) in transition metal oxides is usually associated with a large Hubbard Coulomb interaction U on transition metal ion, which strongly impedes electron motion, as it costs an energy U to add an extra electron to any given site.
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