Pressure-induced magnetically ordered Kondo lattice state in YbCu2Si2

The effect of pressure on the electrical resistivity rho(T) of several YbCu 2Si2 samples was investigated up to 25 GPa and for 30 mK < T < 300 K. With increasing pressure the compound crosses from an intermediate valence state to a magnetic Kondo lattice state at a critical pressure P-C similar to 8 GPa. Below P-C, i.e. in the non-magnetic phase, rho = rho(0) + AT(2) is fou nd at very low temperature, indicating the validity of the Fermi liquid des cription. On approaching the magnetic instability, the A coefficient and th e residual resistivity rho(0) increase strongly. Close to P-C, rho(0) shows a pronounced maximum due to scattering by lattice defects. The pressure va riation of the magnetic resistivity rho(mag) at high temperature is interpr eted in the terms of a pressure induced change of the crystal field splitti ng.