Itinerant spin excitations near the hidden order transition in URu2Si2

TL;DR

This study uses neutron scattering to reveal heavily damped incommensurate spin excitations in URu2Si2, linking their behavior to Fermi surface nesting and a transition from valence fluctuations to a hybridized state at the hidden order transition.

Contribution

It provides evidence that itinerant spin excitations in URu2Si2 are due to Fermi surface nesting, suggesting the hidden order arises from a Fermi-surface instability.

Findings

Heavily damped incommensurate paramagnons observed above T0.

Damping vanishes below the hidden order transition.

Fermi surface nesting likely drives the hidden order phase.

Abstract

By means of neutron scattering we show that the high-temperature precursor to the hidden order state of the heavy fermion superconductor URu$_{2}$Si$_{2}$ exhibits heavily damped incommensurate paramagnons whose strong energy dispersion is very similar to that of the long-lived longitudinal f-spin excitations that appear below T$_{0}$. Since the underlying local f-exchange is preserved we expect only the f-d interactions to change across the phase transition and to cause the paramagnetic damping. The damping exhibits single-ion behavior independent of wave vector and vanishes below the hidden order transition. We suggest that this arises from a transition from valence fluctuations to a hybridized f-d state below T$_{0}$. Here we present evidence that the itinerant excitations, like those in chromium, are due to Fermi surface nesting of hole and electron pockets so that the hidden order phase likely originates from a Fermi-surface instability. We identify wave vectors that span nested regions of a band calculation and that match the neutron spin crossover from incommensurate to commensurate on approach to the hidden order phase.