Origin of the gap-like behavior in pure and doped URu₂Si₂ : A combined study via quasiparticle scattering spectroscopy and resistivity measurements

Using Quasiparticle scattering spectroscopy (QPS), we track the temperature dependence of the hybridization gap in URu_2-xFe_xSi₂ and URu₂Si_2-xP_x (URSP) ^[1,2,3] in all substitutions, whether the hidden order (HO) appears or not. This poses a challenge to the Fermi surface gapping scenario, due to the absence of drastic changes in the conductance spectra across the HO transition. As an alternative way to explain the gap-like behavior, we adopt a model based on gapped bosonic excitations in the ordered state ^[4]. With an unusual temperature dependence of their stiffness, the temperature-dependent resistivity can be reproduced well including the jump at the HO transition. The extracted gap increases with increasing Fe-content, which agrees with the behavior of the E₁ gap in inelastic neutron scattering under pressure. This implies that the E1 gap might originate from the same gapped bosonic excitations.
[1] Park et al PRL 108,246403(2012); [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).