Energy Gap Formation in the Kondo-Lattice Compounds

CeNiSn的运输，热和磁测量的结果表征这种化合物作为一个罕见的例子位于近藤和VF制度之间的交叉附近。这种高度的各向异性行为反映了4f态与Sn-5 p和Ni-3d态在正交结构中的强杂化。该系统的近藤温度约为28 K，当温度低于12 K时，局域自旋涨落的相干性发展，在Pa（T）和Xa（T）中的峰值出现在12 K，在RH（T）中的峰值出现在9 K.当温度低于6 K时，重准粒子带中出现各向异性能隙.这种半导体态的电荷激发能隙为几开尔文，在沿易磁化轴方向施加20 kbar的流体静压或沿着13 T的磁场时都可被破坏。用Co和Pt取代CeNiSn中百分之几的Ni，破坏了能隙，使系统向VF和重费米子区移动，综合结果表明，CeNiSn中的差距形成对4f和传导电子态的杂化程度非常敏感。还强调了近藤晶格相干性的发展对差距的形成至关重要。

The results of transport, thermal and magnetic measurements of CeNiSn characterize this compound as a rare example located near the crossover between the Kondo and VF regimes. The highly anisotropic behavior reflects the strong hybridization of the 4f states with the Sn-5p and Ni-3d states in the orthorhombic structure. The Kondo temperature of this system is about 28 K.At low temperatures below 12K,coherence of local spin fluctuations develops, as indicated by the peaking in both Pa(T) and Xa(T) at 12 K and in RH(T) at 9K.An anisotropic gap opens in the heavy-quasiparticle bands as temperature is reduced below 6 K. This semiconducting state with a charge excitation gap of several Kelvins is destructible by applying either hydrostatic pressure of 20 kbar or magnetic field of 13 T along the easy a axis.Substitutions of Co and Pt for a few percent of Ni in CeNiSn destroy the energy gap and shift the system toward the VF and the heavy-fermion regimes, respectively.The combined results indicate that the gap formation in CeNiSn is very sensitive to the degree of hybridization of the 4f and the conduction electron states. It is also emphasized that the development of coherence in the Kondo lattice is crucial for the gap formation.