We carried out 195Pt-NMR measurements for a single-crystal LaPt2Si2, which is expected to show the coexistence of a superconducting state and a charge density wave (CDW) state. LaPt2Si2 crystallizes to a quasi-two-dimensional CaBe2Ge2-type crystal structure consisting of two types of Pt2Si2 layers: Pt1 and Pt2. From both the Knight shift, 195K, and the NMR relaxation rate divided by the temperature, 1=T1T, the electronic density of states at the Fermi level, N(εF), for only the Pt1 site decreases below the CDW transition temperature T+ = 112 K, whereas N(εF) for the Pt2 site does not change. These results suggest that the CDW occurs only in the Pt1 layers below 112 K. Furthermore, above T+, we also found that both195K and 1=T1T decrease upon cooling only for the Pt1 site. The temperature dependences of K and 1=T1T for the Pt1 site can be explained by assuming a two bands model consisting of a wide band and a narrow band near the Fermi level. The CDW transition is expected to occur only in the narrow band of the Pt1 site, while the wide band of the Pt1-site does not contribute to the CDW transition. The present result strongly indicates that the CDW gap opens partially at the Fermi surface.
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