Fano resonance and the hidden order in URu$_{2}$Si$_{2}$ probed by quasiparticle scattering spectroscopy$^{\ast }$

The nature of the hidden order transition occurring at 17.5 K in URu$_{2}$Si$_{2 }$remains puzzling despite intensive investigations over the past two and half decades. Recent experimental and theoretical developments render it a timely subject to probe the hidden order state using quasiparticle tunneling and scattering techniques. We report on the Fano resonance in pure and Rh-doped URu$_{2}$Si$_{2}$ single crystals using point-contact spectroscopy. The conductance spectra reproducibly reveal asymmetric double peak structures slightly off-centered around zero bias with the two peaks merging well above the hidden order transition temperature. An analysis using the Fano resonance model in a Kondo lattice [1] shows that the conductance peaks arise from the hybridization gap opening. Our estimated gap size agrees well with those reported from other measurements. We will present experimental results over a wide parameter space including temperature and doping dependences and discuss their underlying physics. [1] M. Maltseva, M. Dzero, and P. Coleman, Phys. Rev. Lett. \textbf{103}, 206402 (2009). $^{\ast }$The work at UIUC is supported by the U.S. DOE under Award Nos. DE-FG02-07ER46453 and DE-AC02-98CH10886, and the work at LANL is carried out under the auspices of the U.S. DOE, Office of Science.