# Revealing the Hidden Heavy Fermi Liquid in CaRuO3

## TL;DR

This study uncovers a complex heavy Fermi liquid state in CaRuO3, revealing anisotropic Fermi surfaces and strong electron correlations, which clarify its unusual optical and electronic properties.

## Contribution

First direct measurements of the Fermi surface and quasiparticle dispersion in CaRuO3, highlighting the role of octahedral rotations and heavy quasiparticles in its electronic structure.

## Key findings

- Presence of small electron pockets and straight Fermi surface segments
- Strong band-dependent mass renormalization and heavy quasiparticles
- Temperature-dependent quasiparticle behavior near the Fermi energy

## Abstract

The perovskite ruthenate has attracted considerable interest due to reports of possible non-Fermi-liquid behavior and its proximity to a magnetic quantum critical point, yet its ground state and electronic structure remain enigmatic. Here we report the first measurements of the Fermi surface and quasiparticle dispersion in CaRuO3 through a combination of oxide molecular beam epitaxy and in situ angle-resolved photoemission spectroscopy. Our results reveal a complex and anisotropic Fermi surface consisting of small electron pockets and straight segments, consistent with the bulk orthorhombic crystal structure with large octahedral rotations. We observe a strongly band-dependent mass renormalization, with prominent heavy quasiparticle bands which lie close to the Fermi energy and exhibit strong temperature dependence. These results are consistent with a heavy Fermi liquid with a complex Fermiology and small hybridization gaps near the Fermi energy. Our results provide a unified framework for explaining previous experimental results on CaRuO3, such as its unusual optical conductivity, and demonstrate the importance of octahedral rotations in determining the quasiparticle band structure, and electron correlations in complex transition metal oxides.