Department of Physics and Institute for Quantum Information and Matter, California Institute of Technology, Pasadena, California 91125, USA.
Department of Physics, Harvard University, Cambridge Massachusetts 02138, USA.
Phys Rev Lett. 2023 Apr 7;130(14):147001. doi: 10.1103/PhysRevLett.130.147001.
Twisted bilayer graphene (TBG) exhibits extremely low Fermi velocities for electrons, with the speed of sound surpassing the Fermi velocity. This regime enables the use of TBG for amplifying vibrational waves of the lattice through stimulated emission, following the same principles of operation of free-electron lasers. Our Letter proposes a lasing mechanism relying on the slow-electron bands to produce a coherent beam of acoustic phonons. We propose a device based on undulated electrons in TBG, which we dub the phaser. The device generates phonon beams in a terahertz (THz) frequency range, which can then be used to produce THz electromagnetic radiation. The ability to generate coherent phonons in solids breaks new ground in controlling quantum memories, probing quantum states, realizing nonequilibrium phases of matter, and designing new types of THz optical devices.
扭曲双层石墨烯（TBG）表现出极低的电子费米速度，声速超过费米速度。这种状态使 TBG 能够通过受激辐射来放大晶格的振动波，其工作原理与自由电子激光器相同。我们的信中提出了一种依赖慢电子带产生声子相干光束的激光机制。我们提出了一种基于 TBG 中波纹电子的器件，我们称之为调相器。该器件在太赫兹（THz）频率范围内产生声子束，然后可用于产生 THz 电磁辐射。在固体中产生相干声子的能力为控制量子存储器、探测量子态、实现物质非平衡相以及设计新型 THz 光学器件开辟了新的途径。
