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New answers tagged phonons

0

The main confusion was coming from the $x$ and $y$ axes of the phonon dispersion curves diagram having the same units (cm$^{-1}$), because of the choice of the natural unit system. However, two axes obviously have different meanings. The $x$ axis in the phonon dispersion diagram represents the momenta of phonons, while the $y$ axis represents the energy of ...

3

The answer to your question is, to a minute degree, is yes, since the total energy of something measures its source strength / coupling to gravity. So, if an system has energy $\Delta E$ added to it, it will weigh more - its gravitational mass will increase by $\Delta E/c^2$. Practically, the effect is almost unmeasurable; a magnet's stored magnetic energy ...

4

Because by expanding the sinus term into a taylor expansion, you get $\sin(x)\approx x - \frac{x^3}{6} +\cdots$ So, for small values of k you are allowed to take just the linear term.

5

@GerryHarp's answer contains the gist of the main idea, but there is a point that doesn't quite make sense: There is no such thing as bare ions crystal in solid state physics. To answer your last question: The "bare phonon frequencies" definitely do not refer to phonon frequencies in the absence of electrons. In fact, an ion crystal without electrons is ...

4

Lets start with the bare ions. You set up a linear lattice of protons where the boundaries are held in place by some means. The protons want to get as far apart from each other as possible. So the minimum energy state has the protons spaced on the line with equal distances between them. So yes, the ions form a regular lattice without the electrons. Now ...

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