Local observation of linear-$T$ superfluid density and anomalous vortex dynamics in URu$_2$Si$_2$

TL;DR

This study visualizes superconductivity and ferromagnetism in URu$_2$Si$_2$, revealing a nodal gap consistent with d-wave pairing but lacking expected chiral signatures, thus challenging the chiral superconductivity hypothesis.

Contribution

The paper provides microscopic visualization of superconductivity and ferromagnetism in URu$_2$Si$_2$, demonstrating a nodal gap structure without detectable chirality-related magnetization.

Findings

Linear-$T$ superfluid density consistent with d-wave pairing

Absence of spontaneous magnetization expected for chiral d-wave

Vortex pinning potentials show two- or four-fold symmetry

Abstract

The heavy fermion superconductor URu$_2$Si$_2$ is a candidate for chiral, time-reversal symmetry-breaking superconductivity with a nodal gap structure. Here, we microscopically visualized superconductivity and spatially inhomogeneous ferromagnetism in URu$_2$Si$_2$. We observed linear-$T$ superfluid density, consistent with d-wave pairing symmetries including chiral d-wave, but did not observe the spontaneous magnetization expected for chiral d-wave. Local vortex pinning potentials had either four- or two-fold rotational symmetries with various orientations at different locations. Taken together, these data support a nodal gap structure in URu$_2$Si$_2$ and suggest that chirality either is not present or does not lead to detectable spontaneous magnetization.