[论文解读] Perfect Coulomb drag and exciton transport in an excitonic insulator

Ruishi Qi, Andrew Y. Joe+9 more|arXiv (Cornell University)|Sep 27, 2023

Quantum and electron transport phenomena被引用 10

一句话总结

该论文展示了在 MoSe2/hBN/WSe2 激子绝缘体异质结构中利用新型光谱学实现的完美库仑拖拽与激子输运，揭示在低温下存在非超流激子气体，库仑拖拽可观测至约 15 K。

ABSTRACT

Strongly coupled two-dimensional electron-hole bilayers can give rise to novel quantum Bosonic states: electrons and holes in electrically isolated layers can pair into interlayer excitons, which can form a Bose-Einstein condensate below a critical temperature at zero magnetic field. This state is predicted to feature perfect Coulomb drag, where a current in one layer must be accompanied by an equal but opposite current in the other, and counterflow superconductivity, where the excitons form a superfluid with zero viscosity. Electron-hole bilayers in the strong coupling limit with an excitonic insulator ground state have been recently achieved in semiconducting transition metal dichalcogenide heterostructures, but direct electrical transport measurements remain challenging. Here we use a novel optical spectroscopy to probe the electrical transport of correlated electron-hole fluids in MoSe2/hBN/WSe2 heterostructures. We observe perfect Coulomb drag in the excitonic insulator phase up to a temperature as high as ~15K. Strongly correlated electron and hole transport is also observed at unbalanced electron and hole densities, although the Coulomb drag is not perfect anymore. Meanwhile, the counterflow resistance of interlayer excitons remains finite. These results indicate the formation of an exciton gas in the excitonic insulator which does not condensate into a superfluid at low temperature. Our work also demonstrates that dynamic optical spectroscopy provides a powerful tool for probing novel exciton transport behavior and possible exciton superfluidity in correlated quantum electron-hole fluids.

研究动机与目标

• 推动强耦合电子-空穴双层作为玻色子量子态平台的探索。
• 研究激子绝缘体中层间激子的输运性质。
• 测试在二维半导体异质结构中的完美库仑拖拽与反向流现象。

提出的方法

• 利用新型光谱学探查 MoSe2/hBN/WSe2 异质结构中的电输运。
• 在二维异质结构中制备并研究强耦合的电子-空穴流体。
• 通过光学测量识别库仑拖拽与层间激子输运的特征。

实验结果

研究问题

• RQ1 是否能在二维电子-空穴双层的激子绝缘体相中观测到完美的库仑拖拽？
• RQ2 在变动的电子/空穴密度下，MoSe2/hBN/WSe2 层间激子的输运特性如何？
• RQ3 在低温下激子气体会凝聚成超流态吗，还是保持非凝聚态？
• RQ4 电子与空穴密度不平衡如何影响库仑拖拽和反向流阻力？

主要发现

• 在激子绝缘体相中观察到完美的库仑拖拽，温度升至约 ~15 K。
• 在不平衡密度下观察到强相关的电子和空穴输运，但拖拽并非完全理想。
• 反向流层间激子电阻仍为有限，表明在该区间内不存在超流输运。
• 动态光谱学有效探测相关电子-空穴流体中的激子输运及潜在超流性。