Pomeranchuk instability from electronic correlations in CsTi$_3$Bi$_5$ kagome metal

TL;DR

This paper provides experimental and theoretical evidence that electronic correlations induce a Pomeranchuk instability in CsTi$_3$Bi$_5$, leading to nematicity driven by orbital degrees of freedom in a kagome metal.

Contribution

It combines polarization-dependent ARPES measurements with functional renormalization group calculations to reveal the orbital-selective Pomeranchuk instability in CsTi$_3$Bi$_5$, advancing understanding of nematicity in quantum materials.

Findings

Direct ARPES evidence of orbital nematic deformation.

Identification of a $d$-wave Pomeranchuk instability driven by correlations.

Orbital selectivity plays a key role in symmetry breaking.

Abstract

Among many-body instabilities in correlated quantum systems, electronic nematicity, defined by the spontaneous breaking of rotational symmetry, has emerged as a critical phenomenon, particularly within high-temperature superconductors. Recently, this behavior has been identified in CsTi$_3$Bi$_5$, a member of the AV$_3$Sb$_5$ (A = K, Rb, Cs) kagome family, recognized for its intricate and unconventional quantum phases. Despite accumulating indirect evidence, the fundamental mechanisms driving nematicity in CsTi$_3$Bi$_5$ remain inadequately understood, sparking ongoing debates. In this study, we employ polarization-dependent angle-resolved photoemission spectroscopy to reveal definitive signatures of an orbital-selective nematic deformation in the electronic structure of CsTi$_3$Bi$_5$. This direct experimental evidence underscores the pivotal role of orbital degrees of freedom in symmetry breaking, providing new insights into the complex electronic environment. By applying the functional renormalization group technique to a fully interacting ab initio model, we demonstrate the emergence of a finite angular momentum ($d$-wave) Pomeranchuk instability in CsTi$_3$Bi$_5$, driven by the concomitant action of electronic correlations within specific orbital channels and chemical potential detuning away from Van Hove singularities. By elucidating the connection between orbital correlations and symmetry-breaking instabilities, this work lays a crucial foundation for future investigations into the broader role of orbital selectivity in quantum materials, with far-reaching implications for the design and manipulation of novel electronic phases.