Evidence chain for time-reversal symmetry-breaking kagome superconductivity

TL;DR

This study uncovers time-reversal symmetry-breaking superconductivity in kagome metal Cs(V,Ta)3Sb5, revealing internal magnetism, pairing modulation, and unusual interference effects that challenge conventional understanding of superconductivity and magnetism.

Contribution

It provides the first experimental evidence of time-reversal symmetry-breaking superconductivity in a kagome lattice, linking magnetism and pairing modulation.

Findings

Spontaneous internal magnetism in a full-gap superconducting state

Detection of time-reversal asymmetrical interference of Bogoliubov quasi-particles

Correlation between internal magnetism, quasiparticles, and pairing modulation

Abstract

Superconductivity and magnetism are antagonistic quantum matter, while their intertwining has long been considered in frustrated-lattice systems1-3. In this work, we utilize scanning tunneling microscopy and muon spin resonance to discover time-reversal symmetry-breaking superconductivity in kagome metal Cs(V,Ta)3Sb5, where the Cooper pairing exhibits magnetism and is modulated by it. In the magnetic channel, we observe spontaneous internal magnetism in a full-gap superconducting state. Under perturbations of inverse magnetic fields, we detect a time-reversal asymmetrical interference of Bogoliubov quasi-particles at a circular vector. At this vector, the pairing gap spontaneously modulates, which is distinct from pair density waves occurring at a point vector and consistent with the theoretical proposal of unusual interference effect under time-reversal symmetry-breaking. The correlation between internal magnetism, Bogoliubov quasi-particles, and pairing modulation provides a chain of experimental clues for time-reversal symmetry-breaking kagome superconductivity.