Direct Observation of a Uniaxial Stress-driven Lifshitz Transition in Sr$_{2}$RuO$_{4}$

TL;DR

This study demonstrates how uniaxial stress induces a Lifshitz transition in Sr$_{2}$RuO$_{4}$, revealing the strain's role in enhancing superconductivity and providing a new experimental approach for probing electronic phase transitions.

Contribution

We developed a simple method to apply large uniaxial pressures and directly observed the strain-driven Lifshitz transition in Sr$_{2}$RuO$_{4}$ using angle-resolved photoemission spectroscopy.

Findings

Uniaxial stress causes a Lifshitz transition of the $ ext{γ}$-band Fermi surface.

Strain tuning shifts the van Hove singularity to the Fermi level.

The results constrain theoretical models of strain effects in Sr$_{2}$RuO$_{4}$.

Abstract

Pressure represents a clean tuning parameter for traversing the complex phase diagrams of interacting electron systems and as such has proved of key importance in the study of quantum materials. Application of controlled uniaxial pressure has recently been shown to more than double the transition temperature of the unconventional superconductor Sr$_{2}$RuO$_{4}$ for example, leading to a pronounced peak in $T_\mathrm{c}$ vs. strain whose origin is still under active debate. Here, we develop a simple and compact method to apply large uniaxial pressures passively in restricted sample environments, and utilize this to study the evolution of the electronic structure of Sr$_{2}$RuO$_{4}$ using angle-resolved photoemission. We directly visualize how uniaxial stress drives a Lifshitz transition of the $\gamma$-band Fermi surface, pointing to the key role of strain-tuning its associated van Hove singularity to the Fermi level in mediating the peak in $T_\mathrm{c}$. Our measurements provide stringent constraints for theoretical models of the strain-tuned electronic structure evolution of Sr$_{2}$RuO$_{4}$. More generally, our novel experimental approach opens the door to future studies of strain-tuned phase transitions not only using photoemission, but also other experimental techniques where large pressure cells or piezoelectric-based devices may be difficult to implement.