Impurity-induced transition to a Mott insulator in Sr$_3$Ru$_2$O$_7$

TL;DR

This study demonstrates that minimal Mn doping in Sr$_3$Ru$_2$O$_7$ induces a transition from a paramagnetic metal to an antiferromagnetic insulator driven by electron correlations, revealing impurity effects on Mott physics.

Contribution

It reveals that small impurity doping can induce a Mott insulator transition in Sr$_3$Ru$_2$O$_7$, highlighting impurity-driven electron correlation effects.

Findings

Mn doping causes a metal-insulator transition with a 0.1 eV gap.

The ground state switches from paramagnetic metal to antiferromagnetic insulator.

Long-range orbital order is suggested by magnetic and structural properties.

Abstract

The electrical, magnetic, and structural properties of Sr$_3$(Ru$_{1-x}$Mn$_x$)$_2$O$_7$ (0 $\leq x \leq$ 0.2) are investigated. The parent compound Sr$_3$Ru$_2$O$_7$ is a paramagnetic metal, critically close to magnetic order. We have found that, with a Ru-site doping by only a few percent of Mn, the ground state is switched from a paramagnetic metal to an antiferromagnetic insulator. Optical conductivity measurements show the opening of a gap as large as 0.1 eV, indicating that the metal-to-insulator transition is driven by the electron correlation. The complex low-temperature antiferromagnetic spin arrangement, reminiscent of those observed in some nickelates and manganites, suggests a long range orbital order.