In-situ strain-tuning of the metal-insulator-transition of Ca$_{2}$RuO$_{4}$ in angle-resolved photoemission experiments

TL;DR

This study demonstrates how uniaxial strain can tune the electronic structure of Ca$_{2}$RuO$_{4}$, inducing a transition from Mott insulator to metal, revealed through angle-resolved photoemission spectroscopy.

Contribution

It provides the first in-situ strain tuning of the metal-insulator transition in Ca$_{2}$RuO$_{4}$ using ARPES, revealing detailed electronic structure changes.

Findings

Strain up to -4.1% suppresses the Mott phase.

Metallic state shows a well-defined Fermi surface without pseudogaps.

Charge redistribution occurs within Ru $t_{2g}$ orbitals during transition.

Abstract

We report the evolution of the $k$-space electronic structure of lightly doped bulk Ca$_{2}$RuO$_{4}$ with uniaxial strain. Using ultrathin plate-like crystals, we achieve strain levels up to $-4.1\%$, sufficient to suppress the Mott phase and access the previously unexplored metallic state at low temperature. Angle-resolved photoemission experiments performed while tuning the uniaxial strain reveal that metallicity emerges from a marked redistribution of charge within the Ru $t_{2g}$ shell, accompanied by a sudden collapse of the spectral weight in the lower Hubbard band and the emergence of a well defined Fermi surface which is devoid of pseudogaps. Our results highlight the profound roles of lattice energetics and of the multiorbital nature of Ca$_{2}$RuO$_{4}$ in this archetypal Mott transition and open new perspectives for spectroscopic measurements.