Question

What are Phonons ?

Answer 1

quantum of vibrational energy: a quantum of vibrational or acoustic energy in a crystal lattice

Answer 2

but i think google must have a good knowledge about this topic:D

Answer 3

are they more like particles or like waves ?

Answer 4

so this is main theme of question:D

Answer 5

yeah

Answer 6

As with everything, I'd assume both. An example of a phonon is (I think), in conducting materials, a 'place without electrons near it', or an electron hole. They behave much like particles themselves (or wave-particles, if you prefer).

Answer 7

do they bump into each other or pass through?

Answer 8

Surely a purely elastic bump and passing through each other, given that phonos are just quasiparticles, would be the same phenomenon

Answer 9

In my Science encyclopedia {McGraw Hill}
the description is given as below: - @UnkleRhaukus
Plz pay more attention to last 4 or 5 lines:)





\[\huge{\color{red}{\text{Phonon-}}}\] A quantum of vibrational energy in a solid or other
elastic medium. This vibrational energy can be transported by
elastic waves. The energy content of each wave is quantized.
For a wave of frequency f, the energy is (N + 1/2)hf, where N is
an integer and h is Planck’s constant. Apart from the zero-point
energy, 1/2hf, there are N quanta of energy hf. In elastic or lattice
waves, these quanta are called phonons. Quantization of energy
is not related to the discreteness of the lattice, and also applies to
waves in a continuum.
The concept of phonons closely parallels that of photons,
quanta of electromagnetic wave energy. The indirect consequences
of quantization were established for phonons just as for
photons in the early days of quantum mechanics—for example,
the decrease of the specific heat of solids at low temperatures.
Direct evidence that the energy of vibrational modes is changed
one phonon at a time came much later than that for photons—for
example, the photoelectric effect—because phonons exist only
within a solid, are subject to strong attenuation and scattering,
and have much lower quantum energy than optical or x-ray
photons.
Like photons, phonons can be regarded as particles, each of
energy hf and momentum proportional to the wave vector of the
elastic or lattice wave. Such a particle can be said to transport
energy, thus moving with a velocity equal to the group velocity of
the underlying wave.

Answer 10

why does the energy want to lump into a particle

Answer 11

@UnkleRhaukus a funny thing that I don't know a little bit about this but I was trying to help u through my resources:D

Answer 12

i guess the answer has something to do with the quantisation of vibrations of the lattice

Answer 13

may I attach the rest knowledge of my encyclopedia about phonon?

Answer 14

if it is real good YES

other wise that wont be necessary, i have text books of my own and a whole internet to sift though, i was asking this question here for a less text book style answer.

Answer 15

k:) best of luck for ur answer

Answer 16

A phonon is a quantum of amplitude in a normal mode. That is, imagine a periodic elastic structure, such as a crystal. If it vibrates, you can construct any conceivable vibration out of some combination of the normal mode vibrations, which are vibrations that do not couple to each other (do not transfer energy into or out of each other).

For example, the normal modes of a guitar string are the vibrations that give you the fundamental and the overtones. In principle, if you excite the fundamental mode of the string, it will vibrate indefinitely, without transfering energy to one of the overtones, and vice versa. In a real guitar string, of course this is not true, because the string is not perfectly elastic -- it has "anharmonicities" that allow weak coupling between the normal modes, so that energy in the fundamental will slowly leak into the overtones, and vice versa. But generally the energy transfer is much slower than between NON-normal mode ways of vibrating. You can see this by the very fact that you can excite the normal modes (fundamental + overtones) of the string very easily just by plucking it. Plucking the string excites the string in a way that is nothing like the normal mode vibration -- the string is sharply displaced in one random location. But this energy flows very rapidly into other ways of vibrating, and then, when it flows into the normal modes, gets "stuck" there, because it can only flow elsewhere very slowly. The result is that after plucking the string the energy very rapidly goes into the normal modes and stays there, which is why you hear the fundamental and overtones, and not some random jangly noise.

Classically, the amplitude of -- amoung of energy in -- a normal mode is unrestrcted. It can be a lot or a little, and varies continuously. However, quantum mechanically, it is not. It can be shown that the uncertainty principle directly results in a quantization of the amount of energy in the normal mode amplititudes. (This is often called "second quantization" because it involves the quantization of the amplitudes of fields, as opposed to "first" quantization, which gives you the quantization of frequency and wavelength that naturally occurs to fields that are confined.)

When you quantize the amplitude of the normal modes of an electromagnetic field in a cavity, each quantum of amplitude at a given frequency is called a photon. When you quantize the amplitude of the normal modes of a vibrating solid each quantum of amplitude at a given frequency is called a phonon. The name comes from the Greek phone ("sound") because the vibration of an elastic solid is generally interpreted as a sound wave passing through the solid.

A phonon is a "particle" in that it's a finite chunk of energy. You can have 1 phonon or 2 phonons in a normal mode vibration, but not 1.5 or 1.445, so in that sense it's particle-like. It doesn't have a particular location in coordinate space, however. It's not like a tiny wiggly thing in one corner of the crystal. It has a particular location only in frequency space. Additionally, since phonons are spinless, they are bosons, not fermions, like all particles representing matter, and they are not conserved -- they can be freely created and destroyed, even in an isolated system.