We report linear thermal expansion and magnetostriction measurements for ${\mathrm{CeRu}}_2{\mathrm{Si}}_2$ in magnetic fields up to 52.6 mT and at temperatures down to 1 mK. At high temperatures, this compound showed Landau-Fermi-liquid behavior: The linear thermal expansion coefficient and the magnetostriction coefficient were proportional to the temperature and magnetic field, respectively. In contrast, a pronounced non-Fermi-liquid effect was found below 50 mK. The negative contribution of thermal expansion and magnetostriction suggests the existence of an additional quantum critical point.

• Received 9 October 2008

DOI:https://doi.org/10.1103/PhysRevLett.101.256402