Pt-195-Nmr Evidence For Opening Of Partial Charge-Density-Wave Gap In Layered Lapt2si2 With Cabe2ge2 Structure

We carried out Pt-195-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, K-195, and the NMR relaxation rate divided by the temperature, 1/T1T, the electronic density of states at the Fermi level, N(epsilon(F)), for only the Pt1 site decreases below the CDW transition temperature T* = 112 K, whereas N(epsilon(F)) for the PC 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 both K-195 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.