Temperature Dependence of the Magnetic Penetration Depth and Nodal Gap Structure of UPt$_3$ from Small Angle Neutron Scattering

TL;DR

This study investigates the temperature dependence of the magnetic penetration depth in UPt$_3$, revealing nodal gap structure and suggesting an odd parity chiral superconducting phase through small angle neutron scattering and theoretical analysis.

Contribution

It provides new experimental evidence for the nodal structure of UPt$_3$'s order parameter and proposes an $L=3$ odd parity chiral state as its symmetry.

Findings

Linear temperature dependence of the London penetration depth

Evidence for nodal gap structure

Identification of an $L=3$ odd parity chiral phase

Abstract

Spanning a broad range of physical systems, complex symmetry breaking is widely recognized as a hallmark of competing interactions. This is exemplified in superfluid $^3$He which has multiple thermodynamic phases with spin and orbital quantum numbers $S=1$ and $L=1$, that emerge on cooling from a nearly ferromagnetic Fermi liquid. The heavy fermion compound UPt$_3$ exhibits similar behavior clearly manifest in its multiple superconducting phases. However, consensus as to its order parameter symmetry has remained elusive. Our small angle neutron scattering measurements indicate a linear temperature dependence of the London penetration depth characteristic of nodal structure of the order parameter. Our theoretical analysis is consistent with assignment of its symmetry $L=3$ odd parity state for which one of the three thermodynamic phases in non-zero magnetic field is chiral.