Disorder suppressed charge-density-wave and its origin in 1T-TaSe2-xTex

TL;DR

This study maps the electronic phase diagram of 1T-TaSe2-xTex, revealing disorder suppresses charge-density-wave (CDW) while superconductivity emerges, and suggests CDW originates from phonon-driven lattice distortions affected by disorder.

Contribution

It provides experimental and theoretical insights into how disorder suppresses CDW and induces superconductivity in 1T-TaSe2-xTex, highlighting the role of electron-phonon coupling and lattice distortions.

Findings

CDW is suppressed for 0.5 < x < 1.5

Superconductivity appears for 0.2 < x < 1.2

Disorder, not Fermi surface nesting, suppresses CDW

Abstract

In the sake of connecting the charge-density-wave (CDW) of TaSe$_2$ and single-\emph{\textbf{q}} CDW-type distortion of TaTe$_2$, we present an overall electronic phase diagram of 1\emph{T}-TaSe$_{2-x}$Te$_x$ ($0 \leq x \leq 2$). In the experimentally prepared single crystals, the CDW is completely suppressed as $0.5 < x < 1.5$, while superconductivity emerges as $0.2 < x < 1.2$. Theoretically, similar to 1\emph{T}-TaSe$_2$ and 1\emph{T}-TaTe$_2$, the hypothetic 1\emph{T}-TaSeTe with ordered Se/Ta/Te stacking shows instability in the phonon dispersion, indicating the presence of CDW in the ideally ordered sample. The contradictory between experimental and theoretical results suggests that the CDW is suppressed by disorder in 1\emph{T}-TaSe$_{2-x}$Te$_x$. The formation and suppression of CDW are found to be independent with Fermi surface nesting based on the generated electron susceptibility calculations. The calculation of phonon linewidth suggests the strong \textbf{\emph{q}}-dependent electron-phonon coupling induced period-lattice-distortion (PLD) should be related to our observation: The doping can largely distort the TaX$_6$ (X = Se, Te) octahedra, which are disorderly distributed. The resulted puckered Ta-Ta layers are not compatible with the two-dimensional PLD. Therefore, CDW is suppressed in 1\emph{T}-TaSe$_{2-x}$Te$_x$. Our results offer an indirect evidence that PLD, which can be influenced by strong disorder, is the origin of CDW in the system.