Peculiar Linear Dispersive Bands Observed in Angle-Resolved Photoemission Spectra of Tl-Based Ternary Chalcogenide TlGaTe2

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Electronic energy bands of the Tl-based ternary chalcogenide TlGaTe2 with a quasi one-dimensional crystalline structure have been studied by means of high resolution angle-resolved photoemission spectroscopy (ARPES) in order to check for dispersive structures similar to the Dirac cone observed in the surface bands of Bi-based binary chalcogenides. Two linear dispersive structures which are not reproduced in band calculations for bulk material have been observed in the energy band along the $\Gamma$--N direction perpendicular to the chains. These dispersions form a cross-type structure that is centered at the $\Gamma$ point and extends along the $\Gamma$--H--T direction parallel to the chains, reflecting, in our opinion, one-dimensional features of surface morphology of TlGaTe2. The cross-type structure, the energy position of which linearly varies with excitation photon energy, is observed only for high-grade quality surfaces of TlGaTe2. It is therefore assumed that the observed peculiar dispersive structure is caused by the Dirac-type dispersion of high-lying surface conduction bands and that ARPES detects the joint density of states.
2011-05-25