Yin-Yang vortex on UTe2 (011) surface

TL;DR

This study reports the discovery of Yin-Yang vortices on UTe2 (011) surface, providing evidence for spin-triplet superconductivity and revealing unique vortex structures with distinct local density of states features.

Contribution

The paper presents the first observation of Yin-Yang vortices on UTe2 surface, linking vortex structure to spin-triplet pairing and constraining the pairing symmetry.

Findings

Yin-Yang vortices contain quantized magnetic flux.

Distinct local density of states at vortex regions supports spin-triplet pairing.

Vortex structure aligns with crystallographic a-axis.

Abstract

UTe2 is a promising candidate for spin-triplet superconductor, yet its exact superconducting order parameter remains highly debated. Here, via scanning tunneling microscopy/spectroscopy, we observe a novel type of magnetic vortex with distinct dark-bright contrast in local density of states on UTe2 (011) surface under a perpendicular magnetic field, resembling the conjugate structure of Yin-Yang diagram in Taoism. Each Yin-Yang vortex contains a quantized magnetic flux, and the boundary between the Yin and Yang parts aligns with the crystallographic a-axis of UTe2. The vortex states exhibit intriguing behaviors -- a sharp zero-energy conductance peak exists at the Yang part, while a superconducting gap with pronounced coherence peaks exists at the Yin part, which is even sharper than those measured far from the vortex core or in the absence of magnetic field. By theoretical modeling, we show that the Yin-Yang vortices on UTe2 (011) surface can be explained by the asymmetric vortex-derived local distortion of the zero-energy surface states associated with spin-triplet pairing with appropriate d-vectors. Therefore, the observation of Yin-Yang vortex confirms the spin-triplet pairing in UTe2 and imposes constraints on the candidate d-vector for the spin-triplet pairing.