Recently, Professor Zhou Shuyun, Department of Physics, Tsinghua University, for the first time realized Floquet's instantaneous energy band regulation in semiconductor material black phosphorus and discovered a unique optical selection rule, which laid a solid foundation for regulating material properties and developing new devices. Relevant research results were published in the latest issue of Nature.
The concept of Floquet state has been proposed since the beginning of the 20th century. In the past decade, Floquet instantaneous energy band and physical property control have developed into an important scientific frontier in condensed matter physics and material science in the world, in which the experimental progress in condensed matter system is very little, and many key scientific problems. For example, whether the instantaneous control of band structure can be realized in semiconductors with the application prospects of electronic and optoelectronic devices remains to be confirmed by experiments.
It is understood that the current academic research mainly focuses on the equilibrium characteristics of materials, while the research on non-equilibrium physics and ultrafast dynamics is still in the stage of development. Zhou Shuyun's team used pulsed laser to control the time accuracy to one trillionth of a second, and took a solid step to achieve instantaneous control of material properties. The measurement and control of electronic structure and physical properties on ultrafast time scales (picoseconds or even femtoseconds) will not only expand the frontier of non-equilibrium physics knowledge, but also lay an important scientific foundation for the development and application of new and high-speed devices in the future.
In terms of material system, the research group skillfully selected black phosphorus, a classical semiconductor material with small band gap and high mobility. By fine-tuning the photon energy of the mid-infrared excitation source, the researchers found that when the photon energy is close to resonance with the band gap, the electronic structure of black phosphorus evolves from a parabolic shape in equilibrium to a "Mexican hat" shape that opens a gap at the top of the band, and a replicated Floquet sideband is observed.
"The electronic band structure we studied can be colloquially understood as the DNA of these materials, which determines the various properties of the materials," explained Bao Changhua, a "Shuimu Scholar" at Tsinghua University, one of the main participants in the work. "What we did was to use femtosecond lasers to manipulate the DNA of these materials to obtain some of the properties we wanted."
Source: Science and Technology Daily
