INVESTIGATIONS OF THE ANISOTROPIC SEMICONDIUCTING GAP IN THE HEVY-FERMION COMPOUNDS

首次使用断裂结测量了Ce和Yb基近藤半导体的能隙。由于这项技术提供了最干净的界面，因此有可能研究这种具有非常活跃的表面性质的化合物的内在特征。对于Ce&lt；@D23@&gt；D2Bi&lt；@D24@&gt；D2Pt&lt；@D23@&gt；D2，，虽然形成能隙的机制完全不同，但Di(V)/dV具有清晰的带隙边峰和低的零偏压漏，这与超导隧穿态密度的特征相似。由Di(V)/DV的峰峰分离定义的4.2K下2DELTA(]SYAPPRXEQ[)90 meV的能级远大于由p(T)得到的同一样品的激活能，但与红外测量得到的能级大致相同。比率2DELTA/k&lt；@D2B@&gt；D2T&lt；@D2X@&gt；D2=13(]sy.+-。[)2用T&lt；@D2X@&gt；D2=80K来评估，其中T&lt；@D2X@&gt；D2是感病…的温度更多的能力表现出广泛的最大值。这一比率与CeRhSb和CeNiSn的情况非常一致，在这两种情况下，T&lt；@D2X@&gt；D2以下的间隙打开。这些结果表明，在这些Ce基近藤半导体中，能隙的形成与T&lt；@D2X@&gt；D2直接相关。对于YBB&lt；@D212@&gt；D2，在4.2K的每个结上都观察到非常尖锐的、具有很低零偏置电导漏的带隙边缘结构，由此得到2DELTA()230 meV的平均带隙。这出乎意料地大于从输运测量得到的()12 meV的间隙。升温后，()3000K的巨大温差在60-90K时消失，接近T&lt；@D2X@&gt；D2。在这场比赛中。这一特性类似于基于Ce的近藤半导体。然而，YbB&lt；@D212@&gt；D2的2DELTA/k&lt；@D2B@&gt；D2T&lt；@D2X@&gt；D2()37比具有几乎相同T&lt；@D2X@&gt；D2值的立方Ce&lt；@D23@&gt；D2Bi&lt；@D24@&gt；D2Pt&lt；@D23@&gt；D2化合物的()SY.apprxeq.[)大3倍，从而表明Ybb&lt；@D2X@&gt；D2中产生间隙的特征能量；@D212@&gt；D2比Ce&lt；@D23@&gt；D2Bi&lt；@D24@&gt；D2Pt&lt；@D23@&gt；D2.中的大此外，通过检查Ybb；D212@D2和Ce&lt；@D23@&gt；D2Bi&lt；@D24@&gt；D2Pt&lt；@D23@&gt；D2，的磁化率数据，我们发现每个化合物的结垢温度T&lt；@d1**@>d1，这使得比率2DELTA/k&lt；@D2B@&gt；D2T&lt；@d1**@&gt；d1是(]SY.apprxeq.[)3-4的公共值。

Measurements of the energy gap in the Ce- and Yb- based Kondo semiconductors have been carried for the first time using break junctions. Since this technique provides the cleanest interface, it is possible to investigate the intrinsic features of this compound with very reactive surface properties. For Ce<@D23@>D2Bi<@D24@>D2Pt<@D23@>D2, the features of clear gap-edge peaks and low zero-bias leakage in dI (V) /dV resemble those of the superconducting tunneling density of states, although the mechanism of gap formation is completely different to each other. The gap magnitudes of 2DELTA (]SY.apprxeq.[) 90 meV at 4.2 K defined by the peak-to-peak separation in dI (V) /dV are much larger than the activation energy obtained from p (T) for the identical sample, but are roughly the same magnitude as that obtained from the infrared measurements. The ratio 2DELTA /k<@D2B@>D2T<@D2x@>D2 = 13 (]SY.+-。[) 2 is evaluated using T<@D2x@>D2 = 80 K,where T<@D2x@>D2 is the temperature at which the suscepti … More bility exhibits a broad maximum. This ratio agrees well with that of CeRhSb and CeNiSn, in which the gaps open below T<@D2x@>D2. These results demonstrate that the gap formation is directly connected with T<@D2x@>D2 in these Ce-based Kondo semiconductors. For YbB<@D212@>D2, very sharp gap-edge structures with quite low leakage of the zero-bias conductance are commonly observed in every junction at 4.2 K,from which the average gap value of 2DELTA (]SY.apprxeq.[) 230 meV is obtained. This is unexpectedly larger than the gap of (]SY.apprxeq.[) 12 meV from the transport measurements. Upon warming, this giant gap of (]SY.apprxeq.[) 3000 K reduces to disappear at 60 - 90 K,which is close to the T<@D2x@>D2. of this comound. This feature is similar to that of Ce-based Kondo-semiconductors. However, the ratio 2DELTA/k<@D2B@>D2T<@D2x@>D2 (]SY.apprxeq.[) 37 of YbB<@D212@>D2 is (]SY.apprxeq.[) 3 times larger than that of the cubic Ce<@D23@>D2Bi<@D24@>D2Pt<@D23@>D2 compound having almost the same T<@D2x@>D2 value, thereby indicating that the characteristic energy for the gap creation in ybB<@D212@>D2 is larger than that in Ce<@D23@>D2Bi<@D24@>D2Pt<@D23@>D2. Further, by examining the susceptibility data of YbB<@D212@>D2 and Ce<@D23@>D2Bi<@D24@>D2Pt<@D23@>D2, we find the scaling temperatures T<@D1**@>D1 for each compound, which make the ratio 2DELTA/k<@D2B@>D2T<@D1**@>D1 a common value of (]SY.apprxeq.[) 3 - 4. Less