Mott insulators appearing at thickness period corresponding to nesting in CaRuO_3

TL;DR

This study reveals that in CaRuO_3 thin films, a periodic Mott insulator transition occurs at specific thicknesses due to nesting-induced spin density waves, causing giant resistivity changes linked to antiferromagnetic correlations.

Contribution

It demonstrates a novel size effect in CaRuO_3 where thickness-dependent Mott transitions are driven by nesting and spin density waves, connecting lattice, electronic, and magnetic properties.

Findings

Periodic lattice expansion with 24.8 Å oscillation observed.

Nesting vector identified from Fermi surface analysis.

Thickness-dependent antiferromagnetic correlations induce Mott insulating states.

Abstract

The typical material bismuth shows a several-fold change in electrical resistivity at 4 K over a 400 {\AA} film thickness period. In 2021, we discovered a novel size effect with a period of 25 {\AA} on strongly correlated compound CaRuO_3. The change in film thickness of only one nanometer leads to an increase in electrical resistivity at 4 K by a factor of several billion. However, the excitation energy of 2.4 eV on insulating CaRuO_3 is too large to explain the mechanism by conventional quantum well. In this study, we clarify that the increases in electrical resistivity are accompanied by lattice expansion and caused by the Mott transitions. We measured in-plane X-ray diffraction on CaRuO_3 films and found a 24.8 {\AA} periodic thickness oscillation of the lattice spacing d_{(004)}. We determined the nesting vector from the Fermi surface and revealed the spin density wave with a period equivalent to the size effect. We concluded that the antiferromagnetic correlation appearing in the boundary conditions triggers the periodic Mott insulators depending on the film thickness.