The proximity of a quantum critical point (QCP) for a "metallic" system is expected to generate a non Fermi-liquid (NFL) behavior characterized by "anomalous" temperature dependencies and scaling relations in w/T. Such a NFL behavior has been identified in some heavy-fermion materials like, e.g., (Ce,Au)Cu6 or in some cuprates (parents of high-Tc materials). In particular, the existence of a QCP could explain the crossover from a NFL behavior to a typical Fermi liquid behavior, which is observed at optimal doping in high-Tc materials. It could also explain the magnetic/non-magnetic transition in heavy-fermion systems. Our research program includes investigations of the FL-NFL crossover in heavy-fermion systems (like, e.g., (Ce,La)Ru2Si2...) and in some high-Tc cuprates (YBCO, BISCO,...). For the former systems, a particularly relevant parameter to tune the distance to the QCP is the pressure. This implies to be able to carry out neutron experiments on single crystals at very low temperature under strong uniaxial pressures. Ce(In,Sn)3, URu2Si2 are also among the studied systems.
The Kondo insulator SmS is a key compound due to its valence and insulator to metal transitions at a very low pressure. It is currently beeing revisited taking profit of new generations of macroscopic and microscopic experiments at high pressure, with the aim of gaining new insights into the pressure-temperature phase diagram.