Origin of gaplike behaviors in URu₂Si₂: Combined study via quasiparticle scattering spectroscopy and resistivity measurements

What are the distinct roles played by the localized and itinerant electrons in the hidden order transition of URu₂Si₂? We will show that the hybridization gap observed via quasiparticle scattering spectroscopy shows minimal change upon crossing the phase boundary in the entire phase space of URu₂Si_2-xP_x and URu_2-yFe_ySi₂ [1,2,3]. This suggests its opening is not associated with the ordering. Thus, localized electrons must be the major player. Furthermore, we provide a consistent explanation for the origin of gaps observed only in the ordered states. Taking the gapped bosonic excitations as the dominant scattering source [4], all of our resistivity data including the jump at the transition are replicated. The extracted gap increases with increasing Fe content, similar to the E₁ gap in inelastic neutron scattering [5], suggesting a common origin.
[1]Zhang et al. PRB 102,081101(R)(2020);[2]Gallagher et al. Nat.Commun.7,10712(2016);[3]Ran et al. PNAS 113,13348(2016);[4]Jobiliong et al. PRB 72,104428(2005);[5]Williams et al. PRB 95,104440(2017).