Ferroelectric switching of a two-dimensional metal
Ferroelectric switching of a two-dimensional metal
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DOI：
10.1038/s41586-018-0336-3
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发表时间：
2018-08-16
期刊：
影响因子：
64.8
通讯作者：
Cobden, David H.
中科院分区：
文献类型：
--
作者：
Fei, Zaiyao;Zhao, Wenjin;Cobden, David H.
铁电体是具有极性结构的材料，其极性可以通过施加电场（1，2）来反转（切换）。在金属中，巡回电子屏蔽离子之间的静电力，这部分解释了为什么极性金属非常罕见（3-7）。屏蔽也排除了外部电场，显然排除了铁电开关的可能性。然而，原则上，足够薄的极性金属可以被电场充分穿透以使其极性转换。在这里，我们表明，拓扑半金属WTe 2提供了一个实施例，这一原则。虽然单层WTe 2是中心对称的，因此是非极性的，但堆叠的块体结构是极性的。我们发现，两层或三层WTe 2表现出自发的平面外电极化，可以使用栅电极切换。我们使用石墨烯作为电场传感器直接检测和量化极化（8）。此外，极化状态可以通过电导率来区分，并且可以改变载流子密度以修改性质。极化消失的温度高于350开尔文，并且即使当WTe 2夹在石墨烯层之间时，它也在室温下保持其开关能力，证明了适合与其他二维材料组合应用的鲁棒性（9-12）。
A ferroelectric is a material with a polar structure whose polarity can be reversed (switched) by applying an electric field(1,2). In metals, itinerant electrons screen electrostatic forces between ions, which explains in part why polar metals are very rare(3-7). Screening also excludes external electric fields, apparently ruling out the possibility of ferroelectric switching. However, in principle, a thin enough polar metal could be sufficiently penetrated by an electric field to have its polarity switched. Here we show that the topological semimetal WTe2 provides an embodiment of this principle. Although monolayer WTe2 is centro-symmetric and thus non-polar, the stacked bulk structure is polar. We find that two-or three-layer WTe2 exhibits spontaneous out-of-plane electric polarization that can be switched using gate electrodes. We directly detect and quantify the polarization using graphene as an electric-field sensor(8). Moreover, the polarization states can be differentiated by conductivity and the carrier density can be varied to modify the properties. The temperature at which polarization vanishes is above 350 kelvin, and even when WTe2 is sandwiched between graphene layers it retains its switching capability at room temperature, demonstrating a robustness suitable for applications in combination with other two-dimensional materials(9-12).