Department of Applied Physics, California Institute of Technology, Pasadena, California 91125, USA.
Institute for Quantum Information and Matter, California Institute of Technology, Pasadena, California 91125, USA.
Nat Mater. 2017 Feb;16(2):200-203. doi: 10.1038/nmat4836. Epub 2017 Jan 16.
Layered perovskite iridates realize a rare class of Mott insulators that are predicted to be strongly spin-orbit coupled analogues of the parent state of cuprate high-temperature superconductors. Recent discoveries of pseudogap, magnetic multipolar ordered and possible d-wave superconducting phases in doped SrIrO have reinforced this analogy among the single layer variants. However, unlike the bilayer cuprates, no electronic instabilities have been reported in the doped bilayer iridate SrIrO. Here we show that SrIrO realizes a weak Mott state with no cuprate analogue by using ultrafast time-resolved optical reflectivity to uncover an intimate connection between its insulating gap and antiferromagnetism. However, we detect a subtle charge density wave-like Fermi surface instability in metallic electron doped SrIrO at temperatures (T) close to 200 K via the coherent oscillations of its collective modes, which is reminiscent of that observed in cuprates. The absence of any signatures of a new spatial periodicity below T from diffraction, scanning tunnelling and photoemission based probes suggests an unconventional and possibly short-ranged nature of this density wave order.
层状钙钛矿铱酸盐实现了一类罕见的莫特绝缘体，它们被预测为高温超导铜酸盐母体状态的强自旋轨道耦合类似物。最近在掺杂 SrIrO 中发现的赝能隙、磁多极有序和可能的 d 波超导相，加强了这些单层变体之间的类比。然而，与双层铜酸盐不同，在掺杂的双层铱酸盐 SrIrO 中没有报道电子不稳定性。在这里，我们通过超快时间分辨光反射率研究表明，SrIrO 通过其绝缘能隙和反铁磁之间的紧密联系，实现了一个没有铜酸盐类似物的弱莫特态。然而，我们在接近 200 K 的温度下通过其集体模式的相干振荡，在金属电子掺杂 SrIrO 中检测到一个微妙的电荷密度波状费米面不稳定性，这让人联想到在铜酸盐中观察到的情况。从衍射、扫描隧道显微镜和基于光发射的探针中，在 T 以下没有任何新的空间周期性的迹象表明，这种密度波序具有非常规的、可能是短程的性质。
