Fermi surface of 2H-TaSe2 and its relation to the charge-density wave

The Fermi surface (FS) of 2H-TaSe2 was investigated by high resolution angle resolved photoemission. Two FS pockets, one centered at the Gamma point and the other centered at the K point, were observed and are found to be in excellent agreement with the band calculation results. Although the FS centered at the Gamma point appears to have nested segments with the observed charge density wave (CDW) wave vectors, the CDW-induced energy gap is nearly zero on that FS. Instead, the gap opens in the extended saddle band region and on the FS centered at the K point. The implication of these results on the CDW mechanism is discussed.