Observation of the hybridization gap and Fano resonance in the Kondo lattice URu2Si2

TL;DR

This study uses quasiparticle scattering spectroscopy to identify a hybridization gap and Fano resonance in URu2Si2, revealing that the gap opens above the transition temperature and is not the hidden order parameter.

Contribution

The paper demonstrates a novel spectroscopic approach to detect band renormalizations and Fano resonance in a Kondo lattice, clarifying the nature of the hybridization gap in URu2Si2.

Findings

Hybridization gap opens above the transition temperature.

Asymmetric double-peak structure indicates Fano resonance.

Results constrain the hidden order parameter in URu2Si2.

Abstract

The nature of the second order phase transition that occurs in URu2Si2 at 17.5 K remains puzzling despite intensive research over the past two and half decades. A key question emerging in the field is whether a hybridization gap between the renormalized bands can be identified as the long-sought 'hidden' order parameter. We report on the measurement of a hybridization gap in URu2Si2 employing a spectroscopic technique based on quasiparticle scattering across a ballistic metallic junction. The differential conductance exhibits an asymmetric double-peak structure, a clear signature for a Fano resonance in a Kondo lattice. The extracted hybridization gap opens well above the transition temperature, indicating that it is not the hidden order parameter. Our results put stringent constraints on the origin of the hidden order transition in URu2Si2 and demonstrate that quasiparticle scattering spectroscopy can probe the band renormalizations in a Kondo lattice via detection of a novel type of Fano resonance.