极性金属基异质结SnSe/WTe $_2$中极化状态的电流诱导控制
Current-induced control of the polarization state in a polar metal based heterostructure SnSe/WTe$_2$
摘要：
极性金属的概念为铁电体的电流诱导极化控制提供了新的途径。制备了SnSe/WTe $_2$异质结，实验研究了两种不同极化方向的铁电范德华材料之间的电荷输运。WTe $_2$是具有面外铁电极化的极性金属，而SnSe铁电半导体是面内极化的，因此在SnSe/WTe $_2$界面处应该预期复杂的极化结构。我们研究了$dI/dV(V)$曲线，它表现出尖锐的对称下降到零$dI/dV$微分电导在一些阈值偏置电压$\pm V_{th}$，这是近对称的偏置符号。虽然栅极电场太小而不能显著地影响载流子浓度，但是正阈值位置和负阈值位置对栅极电压敏感。此外，SnSe/WTe $_2$异质结构显示出凹入过渡到低导电$dI/dV=0$状态的突然变化的偏置电压，甚至低于阈值。对于单个SnSe或WTe $_2$薄片不能观察到这种行为，因此我们将其解释为SnSe/WTe $_2$界面耦合的结果。在这种情况下，SnSe/WTe $_2$界面处的电场的某个阈值足以驱动重叠区域中的初始SnSe面内偏振的90 ° $^\circ$变化。极化不匹配导致显著的界面电阻贡献，类似于载流子在畴壁上的散射。因此，我们证明了通过SnSe/WTe $_2$界面的电子输运的极化状态控制。
英文摘要：
The concept of a polar metal proposes new approach of current-induced polarization control for ferroelectrics. We fabricate SnSe/WTe$_2$ heterostructure to experimentally investigate charge transport between two ferroelectric van der Waals materials with different polarization directions. WTe$_2$ is a polar metal with out-of-plane ferroelectric polarization, while SnSe ferroelectric semiconductor is polarized in-plane, so one should expect complicated polarization structure at the SnSe/WTe$_2$ interface. We study $dI/dV(V)$ curves, which demonstrate sharp symmetric drop to zero $dI/dV$ differential conductance at some threshold bias voltages $\pm V_{th}$, which are nearly symmetric in respect to the bias sign. While the gate electric field is too small to noticeably affect the carrier concentration, the positive and negative threshold positions are sensitive to the gate voltage. Also, SnSe/WTe$_2$ heterostructure shows re-entrant transition to the low-conductive $dI/dV=0$ state for abrupt change of the bias voltage even below the threshold values. This behavior can not be observed for single SnSe or WTe$_2$ flakes, so we interpret it as a result of the SnSe/WTe$_2$ interface coupling. In this case, some threshold value of the electric field at the SnSe/WTe$_2$ interface is enough to drive 90$^\circ$ change of the initial SnSe in-plane polarization in the overlap region. The polarization mismatch leads to the significant interface resistance contribution, analogously to the scattering of the charge carriers on the domain walls. Thus, we demonstrate polarization state control by electron transport through the SnSe/WTe$_2$ interface.
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