Structural, vibrational, and electrical properties of 1 T − TiT e 2 under hydrostatic pressure: Experiments and theory
Structural, vibrational, and electrical properties of 1 T − TiT e 2 under hydrostatic pressure: Experiments and theory
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DOI：
10.1103/physrevb.97.085107
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发表时间：
2017-09
影响因子：
3.7
通讯作者：
V. Rajaji;U. Dutta;P. C. Sreeparvathy;S. Sarma;Y. Sorb;B. Joseph;Subodha Sahoo;S. Peter;V. Kanc
中科院分区：
文献类型：
--
作者：
V. Rajaji;U. Dutta;P. C. Sreeparvathy;S. Sarma;Y. Sorb;B. Joseph;Subodha Sahoo;S. Peter;V. Kanc
我们报告了 $1T\text{\ensuremath{-}}\mathrm{TiT}{\mathrm{e}}_{2}$ 的结构、振动和电传输特性，高达 $\ensuremath{\sim}16\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$，这是一个突出的分层二维系统。我们清楚地显示了 $\ensuremath{\sim}2\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$ 和 $\ensuremath{\sim}4\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$ 处的两个同构跃迁的特征，从 $c/a$ 比率的最小值与声子线宽异常相伴随${E}_{g}$ 和 ${A}_{1g}$ 模式围绕相同的压力，提供了与这些跃迁相关的不寻常电子声子耦合的强烈指示。电阻测量在相似的压力范围内呈现非线性行为，揭示了这些压力驱动的同构转变的电子起源。 $\ensuremath{\sim}2\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$ 和 $\ensuremath{\sim}4\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$ 处的电子跃迁的多个间接签名结合最近的理论建议进行了讨论$1T\text{\ensuremath{-}}\mathrm{TiT}{\mathrm{e}}_{2}$ 以及我们的电子费米面计算中电子拓扑跃迁的可能性。在 4 GPa 和 $\ensuremath{\sim}8\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$ 之间，$c/a$ 比率显示出一个平台，表明从各向异性 2D 层到准 3D 晶体网络的转变。第一原理计算表明，在没有任何结构相变的情况下从 2D 到准 3D 的演化主要是由于通过电荷密度重叠增加了层间 Te-Te 相互作用（桥接）。此外，我们在较高压力区域观察到从三角相 ($P\overline{3}m1$) 到单斜相 ($C2/m$) 的一级结构相变。我们估计这种结构相变的开始时间为 $\ensuremath{\sim}8\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$，并且还观察到两个相的共存[三角相 ($P\overline{3}m1$) 和单斜相 ($C2/m$)] $\ensuremath{\sim}8\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$ 到 $\ensuremath{\sim}16\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$。
We report the structural, vibrational, and electrical transport properties up to $\ensuremath{\sim}16\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$ of $1T\text{\ensuremath{-}}\mathrm{TiT}{\mathrm{e}}_{2}$, a prominent layered 2D system. We clearly show signatures of two isostructural transitions at $\ensuremath{\sim}2\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$ and $\ensuremath{\sim}4\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$ obtained from the minima in $c/a$ ratio concomitant with the phonon linewidth anomalies of ${E}_{g}$ and ${A}_{1g}$ modes around the same pressures, providing a strong indication of unusual electron-phonon coupling associated with these transitions. Resistance measurements present nonlinear behavior over similar pressure ranges shedding light on the electronic origin of these pressure-driven isostructural transitions. These multiple indirect signatures of an electronic transition at $\ensuremath{\sim}2\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$ and $\ensuremath{\sim}4\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$ are discussed in connection with the recent theoretical proposal for $1T\text{\ensuremath{-}}\mathrm{TiT}{\mathrm{e}}_{2}$ and also the possibility of an electronic topological transition from our electronic Fermi surface calculations. Between 4 GPa and $\ensuremath{\sim}8\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$, the $c/a$ ratio shows a plateau suggesting a transformation from an anisotropic 2D layer to a quasi-3D crystal network. First-principles calculations suggest that the 2D to quasi-3D evolution without any structural phase transitions is mainly due to the increased interlayer Te-Te interactions (bridging) via the charge density overlap. In addition, we observed a first-order structural phase transition from the trigonal ($P\overline{3}m1$) to monoclinic ($C2/m$) phase at higher pressure regions. We estimate the start of this structural phase transition to be $\ensuremath{\sim}8\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$ and also the coexistence of two phases [trigonal ($P\overline{3}m1$) and monoclinic ($C2/m$)] was observed from $\ensuremath{\sim}8\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$ to $\ensuremath{\sim}16\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$.