Ungapped magnetic excitations beyond Hidden Order in URu$_{2-x}$Re$_x$Si$_2$

TL;DR

This study reveals that Re substitution in URu2Si2 closes the magnetic energy gap associated with Hidden Order, yet magnetic excitations remain ungapped, indicating a complex relationship between magnetic excitations and Hidden Order.

Contribution

It demonstrates that Re substitution closes the magnetic gap without destroying magnetic excitations, challenging previous assumptions about Hidden Order's relationship with magnetic gapping.

Findings

Re substitution closes the magnetic energy gap.

Magnetic excitations remain ungapped despite loss of Hidden Order.

Re substitution does not significantly alter Kondo lattice hybridization.

Abstract

We use inelastic neutron scattering measurements to show that the energy gap in the magnetic excitations of URu$_2$Si$_2$, induced by the Hidden Order transition, is closed by Re substitution. The magnetic excitations remain ungapped in compositions where the specific heat anomaly associated with Hidden Order is no longer observed, which means that the entropy associated with Hidden Order is tied mostly to the magnetic gapping. Further, the onset of ferromagnetic order does not gap the excitations, reflecting the fact that Re substitution does not dramatically affect the Kondo lattice hybridization.