We have studied the magnetotransport properties of the metallic, p-type Sb2Te2Se, which is a topological insulator. Magnetoresistance shows Shubnikov-de Haas oscillations in fields above B=15 T. The maxima and minima positions of oscillations measured at different tilt angles with respect to the B direction align with the normal component of field Bcosθ, implying the existence of a two-dimensional Fermi surface in Sb2Te2Se. The value of the Berry phase β determined from a Landau level fan diagram is very close to 0.5, further suggesting that the oscillations result from topological surface states. From Lifshitz-Kosevich analyses, the position of the Fermi level is found to be EF=250 meV, above the Dirac point. This value of EF is almost 3 times larger than that in our previous study on the Bi2Se2.1Te0.9 topological insulator; however, it still touches the tip of the bulk valence band. This explains the metallic behavior and holelike bulk charge carriers in the Sb2Te2Se compound.
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