It is experimentally known that, at low-temperatures, bulk tantalum diselenide (2H-TaSe2) and tantalum disulfide (2H-TaS2) behave differently when forming charge density wave (CDW) states. In this work, we investigate the reasons and consequences of such differences, using density functional theory (DFT) modeling. We discuss the origins of all CDW modes in both materials, including previously unanalyzed modes. The equilibrium CDW structure of TaSe2 consists of stripes of Ta atoms, while in TaS2 triangles of Ta clusters form. We also determine the nature and direction of the atomic vibrations of the CDW Raman phonons and again find that they are different in the two materials, as well as different in the commensurate and the incommensurate CDW state. For instance, in TaSe2, DFT calculations reveal that Ta atoms vibrate in a circular pattern while in the commensurate CDW state but in a straight line in the incommensurate state. Our results show the power of DFT to advance our understanding of phase change physics in layered materials.

DFT analysis of Raman modes in the CDW states of layered 2H-TaSe2 and 2H-TaS2

2019 Spring National Meeting

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