Electronic structure of the thermoelectric charge density wave material CeTe2-xSbx investigated via angle-resolved photoemission spectroscopy

Abstract

Employing angle-resolved photoemission spectroscopy (ARPES), we have investigated the electronic structures of Sb-substituted CeTe2, CeTe2-xSbx(0 <= x <= 0.5), which exhibit charge density wave (CDW) transitions and enhanced thermoelectric (TE) properties and are also predicted to be topological material candidates. Two flat Ce 4 f states are observed, one at approximately-3.5 eV and the other at approximately-0.8 eV, which represent the 4 f (1)-> 4 f(0 )transition and the Kondo-like 4 f(1) L-0 -> 4 f(1) L(1 )transition (where L & strns; is a ligand hole) of trivalent Ce3+ ions, respectively. Two diamond-shaped inner and outer Fermi surfaces (FSs) are observed, which arise from the holelike band centered at P and from the folding of the two-dimensional Brillouin zone (BZ) into the three-dimensional (3D) BZ, respectively. The measured outer FSs demonstrate the non-negligible effect of the 3D electronic structures of CeTe2-xSbx. The CDW-induced zigzag features are observed in the FS of x = 0, but are not observed in the FSs of x > 0, indicating the rapid suppression of the CDW state by the Sb substitution. This finding suggests that the increased resistivity at x > 0, despite the weakened CDW formation, is possibly due to the disorder-induced localization by the Sb substitution, leading to the optimal TE properties at a specific x. The measured band structures of CeTe(2-x)Sb(x)via ARPES exhibit very similar features for different x values, except for the shift of the whole bands toward the Fermi level (EF) with increasing x. This reflects the hole doping introduced by the Sb substitution, which is in good agreement with the calculated band structures. In the ARPES data of x > 0, crossing bands are observed near the X point at approximately-1 eV, which closely resemble Dirac points, suggesting the existence of topological electronic structures of CeTe2-xSbx. Linear dichroism ARPES measurements on CeTe1.75Sb0.25 show that the EF-crossing Te/Sb p states along X-P-X and M-P-M have both in-plane and out-of-plane character, while those along M-X-M have mainly in-plane character.