The birth of a quasiparticle in silicon observed in time-frequency space

• Published in: Nature Vol. 426; no. 6962; pp. 51 - 54
• Main Authors: Petek, Hrvoje, Hase, Muneaki, Kitajima, Masahiro, Constantinescu, Anca Monia
• Format: Journal Article
• Language: English
• Published: London Nature Publishing 06.11.2003; Nature Publishing Group
• Subjects: Collective effects; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Electron states; Electrooptical effects; Exact sciences and technology; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical properties of bulk materials and thin films; Particle physics; Physics; Silicon; Wavelet transforms; Raman spectra; Semiconductor materials; Time frequency domain method; Electron hole pair; Electron-phonon interactions; Experimental study; Quasiparticles; Reflection spectrum; Electro-optical effects; Silicon; Excitation; Green's function methods; Intraband transitions
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature02044

The concept of quasiparticles in solid-state physics is an extremely powerful tool for describing complex many-body phenomena in terms of single-particle excitations. Introducing a simple particle, such as an electron, hole or phonon, deforms a many-body system through its interactions with other particles. In this way, the added particle is 'dressed' or 'renormalized' by a self-energy cloud that describes the response of the many-body system, so forming a new entity-the quasiparticle. Using ultrafast laser techniques, it is possible to impulsively generate bare particles and observe their subsequent dressing by the many-body interactions (that is, quasiparticle formation) on the time and energy scales governed by the Heisenberg uncertainty principle. Here we describe the coherent response of silicon to excitation with a 10-femtosecond (10-14 s) laser pulse. The optical pulse interacts with the sample by way of the complex second-order nonlinear susceptibility to generate a force on the lattice driving coherent phonon excitation. Transforming the transient reflectivity signal into frequency-time space reveals interference effects leading to the coherent phonon generation and subsequent dressing of the phonon by electron-hole pair excitations.