Coupling between Charge, Lattice, Orbital, and Spin in a Charge Density Wave of 1$T$-TaS${}_2$

Abstract

Two-dimensional layered transition metal dichalcogenide (TMDC) materials often exhibit exotic quantum matter phases due to the delicate coupling and competitions between the charge, lattice, orbital, and spin degrees of freedom. Surprisingly, we here present, based on first-principles density-functional theory calculations, the incorporation of all such degrees of freedom in a charge density wave (CDW) of monolayer (ML) TMDC 1$T$-TaS${}_2$. We reveal that the CDW formed via the electron-phonon coupling is significantly stabilized by the orbital hybridization. The resulting lattice distortion to the "David-star" superstructure constituted of one cental, six nearest-neighbor, and six next-nearest-neighbor Ta atoms is accompanied by the formation of quasimolecular orbitals due to a strong hybridization of the Ta $t_{2g}$ orbitals. Furthermore, the flat band of the quasimolecular orbital at the Fermi level has a spin splitting caused by an intramolecular exchange, yielding a full spin polarization with a band-gap opening. Our finding of the intricate charge-lattice-orbital-spin coupling in ML 1$T$-TaS${}_2$ provides a framework for the exploration of various CDW phases observed in few-layer or bulk 1$T$-TaS${}_2$.

8 pages, 10 figures

References in corpus (3)

• Fermi surface nesting and the origin of Charge Density Waves in metals
• Classification of Charge Density Waves Based on Their Nature
• The low-temperature highly correlated quantum phase in the charge-density-wave 1T-TaS_2 compound

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• Interplay of broken symmetry and delocalized excitations in the insulating state of 1$T$-TaS${}_2$
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