Fermi surface of2H−TaSe2and its relation to the charge-density wave

The Fermi surface (FS) of $2H-{\mathrm{TaSe}}_2$ was investigated by high resolution angle resolved photoemission. Two FS pockets, one centered at the Γ 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 Γ 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.