Temperature dependent tunneling spectroscopy in the heavy fermion CeRu ₂Si ₂ and in the antiferromagnet CeRh ₂Si ₂

CeRu ₂Si ₂ and CeRh ₂Si ₂ are two similar heavy fermion stoichiometric compounds located on the two sides of a magnetic quantum critical phase transition. CeRh ₂Si ₂ is an antiferromagnet below T _N=36K with moderate electronic masses whereas CeRu ₂Si ₂ is a paramagnetic metal with particularly heavy electrons. Here we present tunneling spectroscopy measurements as a function of temperature (from 0.15 to 45K). The tunneling conductance at 0.15K reveals V-shaped dips around the Fermi level in both compounds, which disappear in CeRu ₂Si ₂ above the coherence temperature, and in CeRh ₂Si ₂ above the Néel temperature. In the latter case, two different kinds of V-shaped tunneling conductance dips are found.