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arXiv 2006.15329cond-mat.supr-con
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层间隧穿电流诱导的激子约瑟夫森效应:激子凝聚的有力证据

Excitonic Josephson effect induced by interlayer tunneling current: robust evidence for exciton condensation

Ya-Fen Hsu, Jung-Jung Su

摘要:

约瑟夫森效应可以被认为是激子凝聚的一个显著表现。有人建议通过施加层间隧穿电流来调节双层激子的凝聚相。Huang { \it et al} [Phys. Rev. Lett. $\bf 109$,156802(2012)]证明了在任一边缘处的层间隧穿电流的临界值可以通过在另一边缘处传递第二层间隧穿电流来控制。我们成功地将这种新颖的耦合归因于由隧道电流产生的相对相位引起的激子约瑟夫森效应,并表明黄的实验是激子凝聚的非常有力的证据。我们进一步提出了一个新的建议:存在一个临界约瑟夫森电流,超过这个临界电流,约瑟夫森耦合崩溃,外部电流倾向于转换成边缘态电流,以满足黄在$\pm$ 16 nA以上的第二隧道电流的观察--两个边缘的突然去耦伴随着一个大的边缘间电压。此外,我们还提出了一种通过测量环形激子约瑟夫森结的感应磁场来检测约瑟夫森电流的可行性建议。这一工作不仅解决了激子凝聚识别的长期不确定性,而且为激子凝聚的研究开辟了一个新的方向。

英文摘要:

The Josephson effect can be regarded as a striking manifestation of exciton condensation. It has been suggested to tune the condensate phase of bilayer excitons by applying interlayer tunneling current. A poorly-understood phenomenon observed by Huang {\it et al} [Phys. Rev. Lett. $\bf 109$, 156802 (2012)] demonstrates that the critical values of the interlayer tunneling current at either edge can be controlled by passing a second interlayer tunneling current at the other edge. We successfully attribute this novel coupling to excitonic Josephson effect induced by tunneling-current generated relative phases and indicate that Huang's experiment is very robust evidence for exciton condensation. We furthermore make a new proposal: there exists a critical Josephson current beyond which Josephson coupling collapses and external currents prefer to convert into edge-state currents to meet Huang's observation at the second tunneling current above $\pm$16nA -- a sudden decoupling of two edges accompanied by a large interedge voltage. Also, we make a feasible suggestion to detect Josephson current by measuring induced magnetic field of a ring-shaped excitonic Josephson junction. This work not only solves the long-standing uncertainty regarding the identification of exciton condensation but also opens a new direction to explore exciton condensation.

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