Anisotropic Gap in Quasiparticle Excitations in the Kondo-Lattice System

我们用高质量的单晶研究了YbB12、Ce3Bi4Pt3、CeNiSn3和CeRhSb等近藤晶格系统的能隙形成。新发现如下。各向异性能隙：隧道谱揭示了YbBI2和Ce3Bi4Pt3中的BSC型能隙。在YbB12中用Lu取代Yb，在保持带隙宽度不变的情况下，产生了中间带隙状态。相反，CeNiSn和CeRhSb中的带隙是各向异性的，具有残余态密度。只有1%的CeNiSn掺杂导致残余载流子的单一散射。由于强杂化作用，CeRhSb的带隙各向异性大大减弱。CeNiSn的基态：它是一种载流子密度极低的半金属状态。在0.5K.3K以下，磁阻和比热的反常场依赖关系表明了一种磁极化子。强磁场效应：在沿a轴方向施加14TAU的磁场，使CeNiSn中的空隙闭合。然而，需要30T的高场来弥合CeRhSb中的差距。对于YbB12，在50TAU附近发现了从半导体到金属的一级转变，磁阻的尖峰表明GaP中存在精细结构。压力效应：CeNiSn表现出压力感生磁性，这在Ce基化合物中是第一个例子。

We have studied the gap formation in the Kondo-lattice systems YbB12, Ce3Bi4Pt3, CeNiSn and CeRhSb by means of high-quality single crystals. New findings are as followings.1. Anisotropic Gap : Tunnel spectroscopy revealed the B SC-type gap in YbBI2 and Ce3Bi4Pt3. Substitution of Lu for Yb in YbB12 gives rise to a midgap state with keeping the gap width unchanged. By contrast, the gap in CeNiSn and CeRhSb is anisotropic with a residual density of states. Only 1% substitution in CeNiSn leads to a unitarity scattering of the residual carriers. The gap anisotropy is much weakened in CeRhSb due to the strong hybridization.2. Ground state of CeNiSn : It is a semimetallic state with an extremely low carrier density. A sort of magnetic polaron is indicated by the anomalous field dependence of the magnetoresistance and specific heat below 0.5 K.3. Effect of high magnetic field : The gap in CeNiSn is closed by application of field of 14 TAU along the a axis. However, a higher field of 30 T is required to close the gap in CeRhSb. For YbB12, a first order transition from a semiconductor to a metal is found near 50 TAU The sharp peaks in the magnetoresistance indicate the presence of fine structure in the gap.4. Effect of pressure : CeNiSn exhibits a pressure-induced magnetism, which is the first example among the Ce-based compounds.