Quantum phase transition in the heavy-fermion compound YbIr2Si2

We investigate the pressure-temperature phase diagram of YbIr2Si2 by measuring the electrical resistivity rho(T). In contrast to the widely investigated YbRh2Si2, YbIr2Si2 is a paramagnetic metal below p(c)similar or equal to 8 GPa. Interestingly, a first-order, presumably ferromagnetic, transition develops at p(c). Similar magnetic properties were also observed in YbRh2Si2 and YbCu2Si2 at sufficiently high pressures, suggesting a uniform picture for these Yb compounds. The ground state of YbIr2Si2 under pressure can be described by Landau Fermi-liquid theory, in agreement with the nearly ferromagnetic Fermi-liquid model. Moreover, evidence of a weak valence transition, characterized by a jump of the Kadowaki-Woods ratio as well as an enhancement of the residual resistivity rho(0) and of the quasiparticle-quasiparticle scattering cross section, is observed around 6 GPa.