层状稀土锰氧化物铁电畴壁的低能结构动力学
Low-energy Structural Dynamics of Ferroelectric Domain Walls in Hexagonal Rare-earth Manganites
摘要：
铁性材料中的畴壁（DW），其序参量突然改变其方向，可以承载体畴中不存在的涌现性质。使用宽带（$10^6-10^{10}$ Hz）扫描阻抗显微镜，我们表明，在六方晶系稀土锰氧化物（$h-RMnO_3$）互锁的反相边界和铁电畴壁的电响应是由束缚电荷振荡，而不是自由载流子传导在DW。作为能量耗散率的量度，在GHz频率下$h-RMnO_3$的（001）表面上的DW的有效电导率显著高于在DC下的有效电导率，而在具有面内极化域的表面上不存在该效应。第一性原理和模型计算表明，频率范围和选择规则是一致的DW围绕其平衡位置的周期性滑动。这种类似声波的模式，这是与本地极化和顶端氧原子的同步振荡，是本地化的DW垂直，但自由地沿DW平面传播。我们的研究结果打破了地面了解结构DW动力学和利用新的界面现象的新型器件。
英文摘要：
Domain walls (DWs) in ferroic materials, across which the order parameter abruptly changes its orientation, can host emergent properties that are absent in the bulk domains. Using a broadband ($10^6-10^{10}$ Hz) scanning impedance microscope, we show that the electrical response of the interlocked antiphase boundaries and ferroelectric domain walls in hexagonal rare-earth manganites ($h-RMnO_3$) is dominated by the bound-charge oscillation rather than free-carrier conduction at the DWs. As a measure of the rate of energy dissipation, the effective conductivity of DWs on the (001) surfaces of $h-RMnO_3$ at GHz frequencies is drastically higher than that at dc, while the effect is absent on surfaces with in-plane polarized domains. First-principles and model calculations indicate that the frequency range and selection rules are consistent with the periodic sliding of the DW around its equilibrium position. This acoustic-wave-like mode, which is associated with the synchronized oscillation of local polarization and apical oxygen atoms, is localized perpendicular to the DW but free to propagate along the DW plane. Our results break the ground to understand structural DW dynamics and exploit new interfacial phenomena for novel devices.
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