Semimetal-to-semiconductor transition and charge-density-wave melting in $1T$-TiSe${}_{2-x}$S${}_x$ single crystals

Abstract

The transition metal dichalcogenide $1T$-TiSe${}_2$ is a quasi-two-dimensional layered material with a phase transition towards a commensurate charge density wave (CDW) at a critical temperature T${}_c\approx 200$K. The relationship between the origin of the CDW instability and the semimetallic or semiconducting character of the normal state, i.e., with the non-reconstructed Fermi surface topology, remains elusive. By combining angle-resolved photoemission spectroscopy (ARPES), scanning tunneling microscopy (STM), and density functional theory (DFT) calculations, we investigate $1T$-TiSe${}_{2-x}$S${}_x$ single crystals. Using STM, we first show that the long-range phase coherent CDW state is stable against S substitutions with concentrations at least up to $x=0.34$. The ARPES measurements then reveal a slow but continuous decrease of the overlap between the electron and hole ($e$-$h$) bands of the semimetallic normal-state well reproduced by DFT and related to slight reductions of both the CDW order parameter and $T_c$. Our DFT calculations further predict a semimetal-to-semiconductor transition of the normal state at a higher critical S concentration of $x_c$=0.9 $\pm$0.1, that coincides with a melted CDW state in TiSeS as measured with STM. Finally, we rationalize the $x$-dependence of the $e$-$h$ band overlap in terms of isovalent substitution-induced competing chemical pressure and charge localization effects. Our study highlights the key role of the $e$-$h$ band overlap for the CDW instability.

arXiv comment7 pages, 6 figures

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Cited by in corpus (11)

• Insight into the charge density wave gap from contrast inversion in topographic STM images
• Fermi surface reconstruction and electron dynamics at the charge-density-wave transition in TiSe2
• Semiconductor-metal phase transition and emergent charge density waves in 1T-ZrX${}_2$ (X = Se, Te) at the two-dimensional limit
• Structurally assisted melting of excitonic correlations in 1T-TiSe2
• Electronic structure of TiSe${}_2$ from a quasi-self-consistent G${}_0$W${}_0$ approach
• Phase Separation in the Vicinity of Fermi Surface Hot Spots
• Ultrafast creation of a light induced semimetallic state in strongly excited 1T-TiSe${}_2$
• Trigonal-to-monoclinic structural transition in TiSe${}_2$ due to a combined condensation of $\text{q}=(\frac{1}{2},0,0)$ and $(\frac{1}{2},0,\frac{1}{2})$ phonon instabilities
• Crystal growth, characterization and electronic band structure of TiSeS
• Doping-induced nematic and stripe orders within the charge density wave state of TiSe${}_2$
• Metal-to-insulator transition in Pt-doped TiSe${}_2$ driven by emergent network of narrow transport channels