Strange metal dynamics in SrIrO3

The interplay of electronic correlations, multi-orbital excitations, and strong spin-orbit coupling is a fertile ground for new states of matter in quantum materials. Here, we report on a confocal Raman scattering study of momentum-resolved charge dynamics from a thin film of semimetallic perovskite $\mathbf{SrIrO_3}$. We demonstrate that the charge dynamics, characterized by a broad continuum, is well described in terms of the marginal Fermi liquid phenomenology. In addition, over a wide temperature regime, the inverse scattering time is for all momenta close to the Planckian limit $\mathbf{\tau^{-1}_{\hbar}=k_{\rm B} T/\hbar}$. Thus, $\mathbf{SrIrO_3}$ is a semimetallic multi-band system that is as correlated as, for example, the cuprate superconductors. The usual challenge to resolve the charge dynamics in multi-band systems with very different mobilities is circumvented by taking advantage of the momentum space selectivity of polarized electronic Raman scattering. The Raman responses of both hole- and electron-pockets display an electronic continuum extending far beyond 1000\icm ($\sim$125 meV), much larger than allowed by the phase space for creating particle-hole pairs in a regular Fermi liquid. Analyzing this response in the framework of a memory function formalism, we are able to extract the frequency dependent scattering rate and mass enhancement factor of both types of charge carriers, which in turn allows us to determine the carrier-dependent mobilities and electrical resistivities. The results are well consistent with transport measurement and demonstrate the potential of this approach to investigate the charge dynamics in multi-band systems.

电子关联、多轨道激发与强自旋轨道耦合之间的相互作用，是量子材料中涌现新型物态的重要沃土。本工作针对半金属钙钛矿（perovskite）$oldsymbol{mathrm{SrIrO_3}}$薄膜开展共焦拉曼散射研究，实现了电荷动力学的动量分辨测量。研究表明，以宽连续谱为特征的电荷动力学行为，可以通过边际费米液体（marginal Fermi liquid）唯象理论得到很好的描述。此外，在宽广的温度区间内，所有动量下的散射时间倒数均趋近于普朗克极限（Planckian limit）$oldsymbol{ au^{-1}_{hbar} = frac{k_ ext{B} T}{hbar}}$。由此可见，$oldsymbol{mathrm{SrIrO_3}}$是一种半金属多能带体系，其电子关联强度可与铜基超导体等典型强关联体系相媲美。针对迁移率差异极大的多能带体系，常规手段难以分辨其电荷动力学行为，而本研究借助偏振电子拉曼散射的动量空间选择性，攻克了这一经典难题。空穴口袋与电子口袋的拉曼响应均展现出延伸至1000 cm⁻¹（约125 meV）之外的电子连续谱，远大于常规费米液体中产生粒子-空穴对的相空间所允许的范围。通过在记忆函数形式（memory function formalism）框架下对该拉曼响应进行分析，我们得以提取出两类载流子的频率依赖散射率与质量增强因子，进而获得载流子特异性的迁移率与电阻率。本研究结果与输运测量结果吻合良好，证明了该方法在多能带体系电荷动力学研究中的应用潜力。