Anomalous spin-optical helical effect in Ti-based kagome metal

TL;DR

This paper reports the discovery of an anomalous spin-optical helical effect in Ti-based kagome metal CsTi$_3$Bi$_5$, revealing a new way to detect loop currents through light-matter interactions.

Contribution

It introduces the anomalous spin-optical helical effect as a novel phenomenon linked to loop currents in kagome metals, enabled by light's helicity coupling with spin-orbital correlations.

Findings

Observation of spin handedness-selective signals in CsTi$_3$Bi$_5$

Identification of the effect as a new method to visualize loop currents

Enrichment of understanding of quantum phases in kagome metals

Abstract

The kagome lattice stands as a rich platform for hosting a wide array of correlated quantum phenomena, ranging from charge density waves and superconductivity to electron nematicity and loop current states. Direct detection of loop currents in kagome systems has remained a formidable challenge due to their intricate spatial arrangements and the weak magnetic field signatures they produce. This has left their existence and underlying mechanisms a topic of intense debate. In this work, we uncover a hallmark reconcilable with loop currents: spin handedness-selective signals that surpass conventional dichroic, spin, and spin-dichroic responses. We observe this phenomenon in the kagome metal CsTi$_3$Bi$_5$ and we call it the anomalous spin-optical helical effect. This effect arises from the coupling of light' s helicity with spin-orbital electron correlations, providing a groundbreaking method to visualize loop currents in quantum materials. Our discovery not only enriches the debate surrounding loop currents but also paves the way for new strategies to exploit the electronic phases of quantum materials via light-matter interaction.