Ta₂Ni(SₓSe₁₋ₓ)₅中软声子输运异常的电子调谐
Electronic tuning of the soft-phonon transport anomaly in Ta$_2$Ni(S$_x$Se$_{1-x}$)$_5$
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中文总结 AI 辅助
研究Ta₂Ni(SₓSe₁₋ₓ)₅中软声子输运异常，通过S替代调节能带，发现其与电子不稳定性紧密相关，揭示了该家族在不同端的特性及电子、空穴与晶格相互作用下的软声子输运异常情况。
中文摘要 AI 辅助
Ta₂NiSe₅因其在Tc = 326 K时的相变而持续受到研究，此时它会出现电子能隙和Ta/Ni链的畸变。热输运中在Tc处的一个有趣特征是垂直于链移动的声子的巨大各向异性散射，其微观起源和意义有待阐明。通过用S替代来调节正常态能带重叠/能隙，我们发现了这种软声子输运异常与潜在电子不稳定性之间的紧密联系：当Ta₂Ni(SₓSe₁₋ₓ)₅在高x时接近能带绝缘体且电子跃迁特征被抑制时，软声子输运异常也随之消失。我们的结果为Ta₂Ni(SₓSe₁₋ₓ)₅家族建立了如下图景：在S端附近，单一晶格不稳定性导致Tc接近130 K的弱结构转变。在Se端附近，额外的电子不稳定性将Tc提高到326 K并放大了转变的实验特征。电子、空穴和晶格之间的强相互作用表现为伴随电子涨落的软声子输运异常，包括激子和杂化能隙涨落。
英文摘要
Ta$_2$NiSe$_5$ continues to be investigated for its phase transition at $T_\textrm{c}$ = 326 K, where it develops both an electronic gap and a distortion of its Ta/Ni chains. One intriguing feature at $T_\textrm{c}$ seen in thermal transport is the giant anisotropic scattering of phonons moving perpendicular to the chains, which is apparently associated with the softening of a transverse acoustic phonon, but whose microscopic origin and significance demand clarification. By tuning the normal-state band overlap/gap with S substitution, we uncover a close connection between this soft-phonon transport anomaly and underlying electronic instabilities: When Ta$_2$Ni(S$_x$Se$_{1-x}$)$_5$ approaches a band insulator at high $x$, and signatures of the electronic transition are suppressed, the soft-phonon transport anomaly concomitantly vanishes. Our results establish the following picture for the Ta$_2$Ni(S$_x$Se$_{1-x}$)$_5$ family: Near the S end, a sole lattice instability gives rise to a weak structural transition with $T_\textrm{c}$ approaching 130 K. Near the Se end, additional electronic instabilities boost $T_\textrm{c}$ up to 326 K and amplify experimental signatures of the transition. The strong interaction between electrons, holes, and the lattice is manifested as a soft-phonon transport anomaly accompanied by electronic fluctuations, which include excitonic and hybridization-gap fluctuations.
