Electric and magnetic-properties of the kondo lattice compound cecu2si2

TLDR: In this paper, the authors studied the properties of the Kondo-lattice compound CeCu2Si2 and found that it exhibits a superconducting transition at 0.5 K.

Abstract: Electric, magnetic, and thermoelectric properties of Ce x La1−x Cu2Si2 (0⩽x⩽1) compounds have been studied over a wide temperature interval 0.04 ⩽T⩽300 K in magnetic fieldsH⩽40 kOe. The paramagnetic-magnetic ordering transition temperatureT M is found to rise from ∼0.32 K for cerium concentrationx=0.2 to 1.6 K forx=0.6. A further increase inx from ∼0.8 to 1.0 leads to a decrease inT M . Simultaneously, the susceptibility kink is smeared out and atx≈1.0 it is transformed into temperature-independent enhanced Pauli paramagnetism. The magnetic phase diagram has been found to be similar to that proposed by Doniach for the one-dimensional Kondo-necklace model. The Kondo-lattice compound CeCu2Si2 exhibits a superconducting transition atT c ⋍0.5 K. The variation of the magnetic properties of Ce x La1−x Cu2Si2 from magnetic ordering at 0.2≲x≲0.8 to the nonmagnetic superconducting state atx → 1.0 is caused by the crossover from the magnetic regimeT RKKY≫T K (in which the RKKY temperatureT RKKY exceeds the Kondo temperatureT K) to the nonmagnetic singlet ground state corresponding to the situation whenT K≫T RKKY. This crossover is accompanied by a sharp increase in the low-temperature Hall coefficientR H(T) in Ce x La1−x Cu2Si2 compounds atx → 1. At the same time, a minimum of the negative Seebeck coefficient with a high amplitude appears at 10<T<100 K. The anomalous low-temperature properties of Kondo lattices have been shown to be due to the rise of the narrow Abrikosov-Suhl resonance in the vicinity of the Fermi level eF as the temperature is lowered fromT≫T K toT≪T K. This resonance has a giant amplitude in concentrated Kondo systems and is responsible for the existence in CeCu2Si2 of heavy fermions with extremely low degeneracy temperatureT*F estimated to be 10 K from theR H versusT curve. Further increase of the Kondo coupling constantJ in CeCu2Si2 under pressure induces an increase in (1) the Hall coefficientR H(T=4.2 K), (2) the superconducting transition temperatureT c , (3) the derivative of the upper critical fielddH c2/dT c , and (4) the low-temperature Seebeck coefficientS(T), which have maximum values at the same pressurep K1≈3 kbar, corresponding to the Kondo-lattice state with the maximum amplitude of the Abrikosov-Suhl resonance in CeCu2Si2 atp=p KL. At higher pressuresp>p KL, a continuous transition from the Kondo lattice to the intermediate valence state is observed, which is accompanied by a complete smearing out of the resonance near the Fermi level. Therefore the Kondo lattices represent a new class of solids, which can be characterized as the link between stable magnetism of metals with a deep 4f level and unstable magnetism associated with fluctuating valence. This novel state can be described by a set of anomalous low-temperature properties related to the giant Abrikosov-Suhl resonance near the Fermi level.