Ca-Al-Si三元素可組成兩種不同的混合物CaAlSi和CaAl2Si2，皆具有層狀結構。MgB2是著名的高溫超導，超導溫度39K，CaAlSi和MgB2具有相同結構，同樣具有超導溫度7.8K，所以引起注意。而另一個由Ca-Al-Si三元素組成的化合物為CaAl2Si2，失去超導性質，呈現出半金屬特性。能帶結構計算CaAl2Si2也顯示出在費米面附近出現贗位能。我們藉著NMR的量測，分析隨著不同程度CaAl2-xSi2+x的摻雜，在贗位能上的電子態密度會如何改變。藉著奈特位移(Knight Shift K)和自旋晶格鬆弛時間(spin-lattice relaxation time T1)在77K~300K間的量測結果，我們推得費米面上有能隙的分裂，和理論能帶計算的結果相符。

The ternary Ca-Al-Si systems have two kinds of compound with characteristic layered structure. CaAlSi is a superconductor with transition temperature (Tc) of about 7.8K which is isostructural to MgB2 of high Tc about 39K. The other kind of Ca-Al-Si compound is CaAl2Si2, which shows no superconducting behavior but semimetallic characteristics. Band structure calculation on CaAl2Si2 also resolved a pseudogap in the vicinity of Fermi-level. In this study we examine the electronic states in the pseudogap region of CaAl2-xSi2+x by means of the nuclear magnetic resonance (NMR) spectroscopy. The quadrupole splitting, Knight Shift, and spin-lattice relaxation time ( T1 ) for CaAl2-xSi2+x have been measured between 77K and 300K. We connect these observations to the energy splitting near the Fermi energy, and compare the band-filling behavior to a recent band-structure calculation.

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