Hidden order and hybridization gap in URu₂Si₂ via quasiparticle scattering spectroscopy

The origin of the hidden order transition in URu₂Si₂ still remains unclear despite intensive investigations for almost three decades. It has recently been under debate whether the long-sought hidden order parameter is associated with Fermi surface reconstructions occurring from unconventional hybridizations in this heavy-fermion system. Our quasiparticle scattering spectroscopy based on ballistic metallic junctions provides an important piece of information on this topic. Sensitive to changes in the electronic density of states, this technique enables us to detect the temperature evolution of a hybridization gap between the renormalized bands. Our results show that the hybridization gap opens well above the hidden order transition, implying that it is not the order parameter for the hidden order phase.