Ren Ya-Ning, Cheng Qiang, Sun Qing-Feng, He Lin
Center for Advanced Quantum Studies, Department of Physics, Beijing Normal University, Beijing 100875, China.
School of Science, Qingdao University of Technology, Qingdao, Shandong 266520, China.
Phys Rev Lett. 2022 May 20;128(20):206805. doi: 10.1103/PhysRevLett.128.206805.
The Berry phase plays an important role in determining many physical properties of quantum systems. However, tuning the energy spectrum of a quantum system via Berry phase is comparatively rare because the Berry phase is usually a fixed constant. Here, we report the realization of an unusual valley-polarized energy spectra via continuously tunable Berry phases in Bernal-stacked bilayer graphene quantum dots. In our experiment, the Berry phase of electron orbital states is continuously tuned from about π to 2π by perpendicular magnetic fields. When the Berry phase equals π or 2π, the electron states in the two inequivalent valleys are energetically degenerate. By altering the Berry phase to noninteger multiples of π, large and continuously tunable valley-polarized energy spectra are realized. Our result reveals the Berry phase's essential role in valleytronics and the observed valley splitting, on the order of 10 meV at a magnetic field of 1 T, is about 100 times larger than Zeeman splitting for spin, shedding light on graphene-based valleytronics.
贝里相位在确定量子系统的许多物理性质方面起着重要作用。然而，通过贝里相位来调节量子系统的能谱相对较少见，因为贝里相位通常是一个固定常数。在此，我们报告了在伯纳尔堆叠双层石墨烯量子点中通过连续可调的贝里相位实现了一种不寻常的谷极化能谱。在我们的实验中，电子轨道态的贝里相位通过垂直磁场从约π连续调节到2π。当贝里相位等于π或2π时，两个不等价谷中的电子态在能量上是简并的。通过将贝里相位改变为π的非整数倍，实现了大的且连续可调的谷极化能谱。我们的结果揭示了贝里相位在谷电子学中的关键作用，并且在1 T磁场下观察到的谷分裂约为10 meV，比自旋的塞曼分裂大100倍左右，这为基于石墨烯的谷电子学提供了新的思路。
