Further analysis of the quantum critical point of Ce1−xLaxRu2Si2

Recent leading topics in heavy fermion (HF) compounds physics are unconventional superconductivity and marginal Fermi liquid behaviour. Since these phenomena often occur in the vicinity of a magnetic instability, the concept of quantum phase transition has attracted a lot of attention both on experimental[1, 2] and theoretical[3, 4, 5] sides. Such a transition between a magnetically ordered state and a paramagnetic state occurs at T=0 K for a critical value, rc, of a non thermal tuning parameter r (r being experimentally controlled by pressure, alloying or magnetic field). The T=0 K, r=rc point of the phase diagram is called the quantum critical point (QCP). Inelastic neutron scattering (INS) is a key probe to study spin fluctuations at a QCP in order to know to which extend the characteristics of the dynamical spin susceptibility can explain the anomalous bulk properties of these materials. Peculiar behavior is expected because statics and dynamics are inextricably mixed at T=0 K. As a consequence, the effective dimension of the system deff equals d+ z, where d is the space dimension and z is the dynamical exponent [6, 7]. This implies that a quantum critical system is in better position to be above the upper critical dimension than a classical one. Thus a mean field behavior is therefore expected at the QCP. While many INS studies have been performed near the QCP, only a few works were extensively performed on single crystal samples where the full wavewector (q) dependence can be investigated. Such studies concern CeCu6 doped with Au (Karlsruhe group), CeRu2Si2 doped with La (Grenoble group) and doped with Rh (Tokyo-Osaka group). For the system Ce1−xLaxRu2Si2, large single crystals of good quality are available for several concentrations x [8]. The three dimensional Ising compound CeRu2Si2 [9] is an archetypal HF system with a Pauli paramagnetic ground state. Strong correlations between lattice,