solids and some liquids. In the context of optically trapped objects, the quantized vibration mode can be defined as phonons as long as the modal wavelength
A phonon is a quasiparticle, collective excitation in a periodic, elastic arrangement of atoms or molecules in condensed matter, specifically in solids and some liquids. In the context of optically trapped objects, the quantized vibration mode can be defined as phonons as long as the modal wavelength of the oscillation is smaller than the size of the object. A type of quasiparticle in physics, a p
A phonon is a quasiparticle, collective excitation in a periodic, elastic arrangement of atoms or molecules in condensed matter, specifically in solids and some liquids. In the context of optically trapped objects, the quantized vibration mode can be defined as phonons as long as the modal wavelength of the oscillation is smaller than the size of the object. A type of quasiparticle in physics, a phonon is an excited state in the quantum mechanical quantization of the modes of vibrations for elastic structures of interacting particles. Phonons can be thought of as quantized sound waves, similar to photons as quantized light waves.
The study of phonons is an important part of condensed matter physics. They play a major role in many of the physical properties of condensed matter systems, such as thermal conductivity and electrical conductivity, as well as in models of neutron scattering and related effects.
The concept of phonons was introduced in 1930 by Soviet physicist Igor Tamm. The name phonon was suggested by Yakov Frenkel. It comes from the Greek word φωνή (phonē), which translates to sound or voice, because long-wavelength phonons give rise to sound. The name emphasizes the analogy to the word photon, in that phonons represent wave-particle duality for sound waves in the same way that photons represent wave-particle duality for light waves. Solids with more than one atom in the smallest unit cell exhibit both acoustic and optical phonons.
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By analogy to photons and matter waves, phonons have been treated with wavevector k as though it has a momentum ħk; however, this is not strictly correct, because ħk is not actually a physical momentum; it is called the crystal momentum or pseudomomentum. This is because k is only determined up to addition of constant vectors (the reciprocal lattice vectors and integer multiples thereof). For example, in the one-dimensional model, the normal coordinates Q and Π are defined so that
The thermodynamic properties of a solid are directly related to its phonon structure. The entire set of all possible phonons that are described by the phonon dispersion relations combine in what is known as the phonon density of states which…
O (1D) systems have always captured the imagination of physicists. In the ultimate 1D limit, a crystal is nothing but a string of atoms, akin to a necklace of tiny pearls. Most physics graduates undoubtedly associate 1D systems with the simple models used in introductory level quantum mechanics or statistical mechanics courses. Indeed, 1D model systems represent pedagogical and often most useful illustrations of the basic physics principles that govern more realistic condensed matter systems. These principles tell us, for instance, that an ideal atomic chain with a single metallic band should be unstable with respect to a Peierls distortion. A Peierls distortion is a condensed state of the 1D electron gas whose formation is triggered by the strong coupling between electrons and quantized lattice vibrations (phonons). The upshot is that such a wire would not conduct electricity at low temperature. Alternatively, atom wires could display exotic many-body physics. It has been predicted that, due to strong electron-electron interactions in 1D, the concept of single electrons should even break down and that it is only meaningful to discuss their collective behavior (i.e., excitations). Such a state of matter is referred to as the Luttinger-Tomonaga liquid. But even though the theory of ideal 1D systems has advanced much, experimental realization of truly 1D condensed matter systems remains a daunting task; it is impossible to suspend a long string of atoms in free space. Nonethele
Phonons, the quantized vibrations of crystal lattices, are essential to determining the material properties. At (sub)nanoscale, surfaces, heterointerfaces, crystal defects, and other imperfections generate localized phonon modes that can significantly alter materials' thermal, electrical, optical, and mechanical properties. However, conventional techniques often struggle to probe these localized phonon modes due to limitations in spatial resolution, momentum transfer, and penetration depth. Recent advancements in electron energy loss spectroscopy in scanning transmission electron microscopy (STEM-EELS) have overcome these challenges, achieving (sub)nanometer spatial resolution, several Brillouin Zones of momentum transfer, and millielectronvolt energy resolution, providing opportunities to probe the local phonons and their properties. This Review examines the theoretical framework of resolution control and local phonon detection in STEM-EELS, while comprehensively discussing experimental advancements and their applications in various materials systems. Given its flexibility to finely tune both spatial and momentum resolutions, this approach enables precise detection of local phonon density of states in defect structures, heterointerfaces, and nanoscale systems, as well as achieving nanometer-scale spatial resolution for phonon dispersion measurements. Additionally, the application and potential of such a method for studying thermal, electrical, and optical properties as well as detecting vibrations in molecules are also discussed. With rapid development, vibrational STEM-EELS is expected to play an increasingly important role in materials science, condensed matter physics, and chemistry in the future.
Ultrafast pump-probe spectroscopy is a powerful experimental technique to study the light-matter interaction and ultrafast dynamics in solids. In many semiconductors, under ultrafast laser irradiation, phonons (quantized lattice vibrations) with both temporal and spatial coherence can be generated conveniently. When a stronger laser pulse excites coherent phonons that induce refractive index change, and thus the reflectivity change of the materials, the time-dependent phonon dynamics can be detected by a delayed probe pulse. The generation and detection of coherent phonons provide an opportuni
Discussed are how the thermal vibrations of a solid are described in terms of lattice waves, how these waves interact with other waves, or with themselves, and how one is led from such a description in terms of waves to the concept of a phonon. (Author/MA)
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